I thought it would be fun to periodically highlight some insects that are understudied or lesser-known. Today’s insect spotlight is on the marigold fruit fly, Trupanea vicina. If you grow marigolds in your garden, you might find this fruit fly or it’s larvae in your flowers. One of its most striking features is the bold, patterned wings that is has, I think the venation almost resembles shattered glass. This is a fly in the tephritid fruit fly family, a large group of flies that often specialize on flowers and seeds. There are over 4,000 species in this family of fruit flies and there are likely many more undiscovered ones. Flies in this group might be confused with kitchen fruit flies, which belong to Drosophilidae family and are usually quite small. Tephritids are larger and often have striking wing patterns which are used during courtship or to ward off predators. The group includes important agricultural pests such as Mexican fruit flies olive fruit fly.
Marigold fruit fly adults are about 4–5 mm long with banded or spotted wings. Research suggests that T. vicina primarily develops in marigolds, where the larvae feed inside flower heads (Foote et al. 1993). We don’t know to what extent it will use other host species of asters, though tephritids tend to be specialized with very close relationships to their preferred host plant. So far the species has been observed in California, Arizona, Mexico, and other parts of Central America, though its full distribution has not been systematically mapped, and I would be curious to know if you’ve seen it in any other region.
There’s a lot we don’t know about the fruit fly. While this is a pest of low concern, it’s unclear how much damage it causes to marigolds. The larvae do consume developing seeds, but we are unsure if this always reduces the quality of flower or only in cases of extreme infestation. This is the first year that I am getting reports of marigold fruit fly being an issue in home gardens in Southern California. Have you experienced it before?
References
Foote, R. H., F. L. Blanc, and A. L. Norrbom. 1993. Handbook of the Fruit Flies (Diptera: Tephritidae) of America North of Mexico. Cornell University Press, Ithaca, NY.
The cooler weather that many parts of the eastern United States are experiencing this week is causing many gardeners to think about what this fall will be like. In fact, many farmers in Georgia are already planting fall crops, and I am sure that many gardeners are also busy with their own fall planting if they live in the Northern Hemisphere mid-latitudes. In this blog post we will discuss seasonal forecasts and how you can use them to plan and plant your garden.
Sumac turning orange in early fall, ShenandoahNPS, Commons Wikimedia.
What kinds of long-range forecasts are available?
In weather and climate, there are two basic types of forecasts. The first is a deterministic forecast, which gives an outlook that describes the specific weather that is expected to occur at a discrete time in the future. Deterministic forecasts are commonly used for weather forecasts for the next few days and are based on computer model predictions that are grounded in the physical equations of motion, thermodynamics and other properties of the atmosphere. Generally, deterministic forecasts are most useful within a few days after the forecast is made. As you go farther out in time, they become less accurate due to lack of updated weather observations and drifts in the models due to the chaotic nature of the atmosphere. In general, a deterministic forecast is not very accurate more than a week ahead of when it is made. They are better than they used to be, and the accuracy of a 7-day forecast now is as good as a 5-day forecast was a couple of decades ago, but we will likely never have a perfect deterministic forecast more than ten days out.
Longer-term forecasts are usually given as probabilistic forecasts. In other words, the forecast will give a likelihood of occurrence of general weather conditions such as wetter or drier and colder or warmer than normal. For meteorologists, “normal” is a 30-year average of temperature and precipitation at a location and is currently based on the 1991-2020 period (they are updated every ten years due to the amount of work it takes to produce a clean dataset). Most probabilistic forecasts are based on multiple model results that start from slightly different conditions and are built with different methods of creating rain and clouds, moving temperature and humidity around, and start with different surface conditions. The more the models agree, the higher the probability of occurrence of a particular type of weather.
How to interpret the NOAA monthly and season forecast maps
In the NOAA map for September 2025 above, for example, there is a dark brown area centered on the Great Salt Lake in the western United States. This is an area that has a strong probability of being drier than normal in the month of September based on the available model output. The fact that it is dark brown does not mean it will necessarily be much drier than normal, but that we have a strong likelihood that it will in the lowest third of years in terms of how many inches of precipitation it is likely to experience. These forecasts start from even odds of having near normal precipitation (34%), above normal precipitation (33%) and below normal precipitation (33%). If the climate forecast models indicate mostly dry conditions at a point, then the percentages shift to something more like 34% near normal, 50% below normal, and 16% above normal precipitation. Because there is so much uncertainty in the atmosphere, you never know with total accuracy which category the season will fall into, you just have some confidence of which way it is likely to fall. Since this is the average for an entire month or season, there can be periods within that time span that are significantly different weather that what the probabilities suggest are the most likely to occur. Here is a list of what the seasonal forecast maps do NOT tell us.
If you are planning an outdoor event like a garden wedding months ahead, a deterministic forecast is what you would probably want to know. Do we need to rent a tent? Should we expect hot or cold weather when we purchase a dress? Unfortunately, this is not possible a long time ahead and so you need to use previous or average weather conditions on that date to decide what kind of weather is most likely to occur and be aware that you could be wrong. There are a few commercial forecasting sites that provide specific deterministic forecasts up to 90 days ahead. I asked a friend who works for one of these companies why they do it when research shows that there is no skill involved, and he told me they do it for “entertainment value.” In other words, it is not real information, it is just click-bait. The same thing happens with wild hurricane forecasts on social media that show a single deterministic forecast of a huge storm hitting somewhere like Tampa, conveniently not showing the 99 models with no such storm present. Don’t believe them, they are harvesting clicks, not providing useful information.
Early fall leaf against sandstone, cogdogblog, Commons Wikimedia.
The Farmers’ Almanac and the Old Farmer’s Almanac
Every year, including this one, publishers release almanacs each fall which claim to show what the weather will be like for 1 to 3-day periods for the winter and next year. Their winter outlook maps get a lot of press about what to expect weatherwise for the next few months (I won’t post any links in this post but you can search online if you are really curious). If you read them carefully, you can see they are quasi-deterministic since they reference storms or heat waves occurring at specific areas over just a few days, although they are usually written in broad enough language that they can be interpreted in several ways. Many people use these for planning their gardens, and they do contain useful information about climatological conditions, average frost dates, and sunrise and sunset information. But scientists have shown that they are only about 50% accurate, which amounts to pure chance. They base their forecasts on secret formulas that cannot be scientifically studied or verified so we have no way to know what they are really using to determine what those forecasts will be. So if you buy one this year, I challenge you to keep track of what they forecast and what weather actually occurred at your house and see if they did any better than chance in 2026. Let the buyer beware and use them for “entertainment value” only.
What can we expect this fall?
Based on NOAA’s probabilistic forecast, we can expect the temperature across most of the United States to be warmer than normal, with some areas more likely to be warm than others. This is likely due to the continuing greenhouse warming that is occurring, making every year (on average) warmer than the previous one, although there is a lot of variation within that trend from one year to the next. Precipitation in the Southeast for the September through November period is leaning towards wetter than normal conditions, and that is probably related mostly to the second half of the Atlantic hurricane season, which could bring heavy rain to parts of the Southeast during fall even though parts of it will certainly be missed. The southwestern United States centered on the Four Corners area is expected to be drier than normal in an area that is already quite dry climatologically.
For the December through February period, the forecast is showing a pattern of climate conditions that is consistent with the La Nina that is expected to occur as we head into winter, with warmer and drier conditions in the southern US and wetter and cooler conditions in the northern US. If you live in a different part of the world, you can find images of the expected La Nina conditions here. Choose plants according to the climate conditions you expect and be prepared to manage them for those conditions, so that if you are in the South, you may have to water more frequently because of the drier than average conditions.
Seasonal outlook maps can provide clues to the kind of temperature and rainfall conditions you are likely to experience in your neighborhood over 3-month periods, although they will not give you specific details about when the first frost might occur or how many heavy rain events you can expect to see. But knowledge of the likely pattern of conditions you can expect will allow you to plan what kind of plants to put in the ground and how you are likely to have to take care of them as they grow.
Just an additional note: If you like to track the fall colors, check out this interactive fall foliage map at https://www.explorefall.com/, now including Alaska. It’s a great resource for planning weekend trips to areas you think will be experiencing beautiful fall foliage.
Backlit grass in the early fall at Shenandoah Valley Outlook, ShenandoahNPS, Commons Wikimedia.
Pesticide residues and risk assessments have been a major topic of interest and inquiry for me for over a decade, and something that I wanted to write about on the Blog for quite some time. Over the past couple of months, I have had several inquiries from people regarding the “Dirty Dozen” list, so I thought this was the perfect time to organize the evidence-based data on this topic. To see a prior post on this topic, you should also check out Jeff Gillman’s post on the Dirty Dozen from 2010 and a follow up post from 2011.
Before diving too deeply, I wanted to acknowledge some of the articles and resources that I leaned heavily on while putting this post together. These include an excellent article by University of California Davis Extension Food Toxicologist Dr. Carl Winter on pesticidefacts.org, and an article authored by multiple experts from University of Arkansas Division of Agriculture Research & Extension (Dr. Amanda McWhirt, Dr. Jackie Lee, and Ples Spradley). Since both of these articles are over 5 years old, I have updated some of the information in my post to reflect any changes in the science and methodology since the time their articles were published. I also want to acknowledge that much of the regulatory information that I will be sharing within this post will pertain to agriculture in the United States, and for more detailed information on this topic pertaining to other countries, I strongly encourage you to seek out evidence-based resources and/or reach out to knowledgeable experts.
What is the ‘Dirty Dozen’
Aside from being a great World War II film from the late 1960’s, the term ‘Dirty Dozen’ also refers to a consumer-focused publication put together by an environmental advocacy group based in the United States. The Dirty Dozen is a list of 12 produce items (fruits and veggies) that allegedly contain the highest pesticide residue levels (dubbing them to be the ‘dirtiest’). This list is developed annually by the Environmental Working Group (EWG) with rankings that are based on United States Department of Agriculture’s (USDA) Pesticide Data Program (PDP) report. Although this sounds important and valuable to share with consumers, the information contained in these lists is derived through problematic methodology, disseminated using a lack of complete and evidence-based data, and results in unnecessary fear and uncertainty surrounding the consumption of fruits and vegetables that can have significant negative ramifications for growers and consumers alike.
The EWG’s “Shopper’s Guide to Pesticides in Produce” deters people from buying conventionally grown produce on the “Dirty Dozen” list, encouraging them to only purchase organic versions of these items. This annual guide also contains a “Clean Fifteen” list which includes produce items with the “lowest amounts of pesticide residues”. Neither list goes into detail regarding what these residues actually are, and whether they are even harmful to the consumer, and are therefore continually challenged by many scientists as lacking in scientific credibility.
Prior to 2025 EWG’s Dirty Dozen list was formulated primarily using percentages of samples with detectible pesticides and the number and amount of pesticides detected (with absolutely no information regarding the relative toxicity of these pesticides). As of this year, they have included the metric “overall toxicity of pesticides on a crop” as part of their screening criteria. Although this is a step in the right direction, it is still arguably incomplete information to share with consumers (especially since the most important component, whether these residue amounts are actually harmful to consumers, is still not addressed by any of their metrics, nor clearly communicated in their publications and marketing). This glaring omission is a big red flag in the credibility of this publication, and one of the main reasons why I have such a problem with it. As many of you avid Garden Professors Blog readers know from the many great science-based posts that have been shared (including Linda’s article on Recognizing Bad Science), we need to look carefully at the information being shared, regardless of the source, and make sure that it is evidence-based, credible, and complete.
Understanding Pesticide Safety
I want to caveat this section by stating that this is covering the science pertaining to pesticides and human health based on the research we have on this topic to date (which is subject to change as more evidence-based information comes to light). The scope of this Blog post does not cover environmental/ecological/economic/etc. impacts of pesticides in general nor the overarching impacts of various types of agriculture and food production systems (both of these are very complex topics which will require much more time and research to cover).
Although the term ‘pesticide’ is synonymously used with insecticides by many, pesticides are actually a broad category that includes all substances used to control or eliminate pests (including weeds, arthropods, vertebrate pests, pathogens, etc.). Therefore herbicides, insecticides, miticides, rodenticides, fungicides, bactericides, etc. all fall within the category of ‘pesticides’. Humans have been using ‘pesticides’ for thousands of years, though much of the innovation in pesticides (especially synthetic formulations) has occurred over the past 100 years. We have also greatly expanded our understanding and implementation of safety protocols and consideration for human and environmental health especially over the past 50 years (since Rachel Carson’s ‘Silent Spring’ and the formation of the U.S. Environmental Protection Agency (EPA) in 1970). Thankfully we have come a long way from the ‘DDT is good for ME-E-E’ era (and still have quite a long way to go). Although we are not perfect, pesticides in general are continuing to become safer and more effective, and products with higher toxicity and non-target effects are continually being phased out in support of better chemistries with fewer human health and environmental impacts (though the latter has much more knowledge gaps than the former, and we still have a LOT more work to do on this front). As we learn more about these products with scientific studies, we continue to update our protocols pertaining to them, though there are still knowledge gaps which continue to be explored by researchers. As Extension and IPM (Integrated Pest Management) professionals, we continue to educate people on the importance of pesticide safety, and urge people to think of the environmental impacts of these products, using them only after other IPM strategies (such as cultural, mechanical, and biological controls) have been unsuccessful. Anyone who uses pesticide products (whether Restricted Use Pesticides applied by Certified Pesticide Applicators and those under their direct supervision, or readily available general use pesticides such as Neem Oil, Insecticidal Soaps, etc.) should do so responsibly and in accordance with the label (the label is the LAW!), only when needed, and minimize negative environmental impacts when possible. The history of pesticides and formation of current regulatory protocols is a fascinating topic that I encourage all of you to read up on if you are interested (and may be an interesting topic for a Blog post in the future).
Now that we have covered pesticide basics, let’s get into pesticides and food safety in Organic and Conventional agriculture. First and foremost, if you are purchasing organic produce, that does not mean it is pesticide-free. In the United States, Certified Organic produce refers to food items that are grown utilizing a specific set of principles governed by the National Organic Program. Furthermore, there could be several conventional operations that still follow some of these principles, though may not be Certified Organic. An organic pesticide is basically a pesticide that is approved by the USDA for use in organic agriculture. Although pesticides used in organic agriculture are usually naturally derived, there are also synthetic pesticides that meet the criteria and are allowed in organic agriculture (just as there may be organic pesticides used in conventional agriculture). All pesticides utilized in the U.S. (with the exception of minimum risk pesticides) are registered with and regulated by the EPA. Any of the aforementioned pesticides that are used and sold within the U.S. have rigorous testing surrounding their safety for humans (and maximum allowable concentrations which are set at levels significantly below [10-1000 times lower] those that caused no adverse effects during testing), labeled according to these appropriate evidence-based safety guidelines, and off-label use is prohibited, routinely investigated, and enforced. Regardless of organic/conventional designation: just because something is naturally derived does not mean that it is safer than synthetically derived products. There are many natural substances that are extremely toxic (eg. Botulinum toxin, Ricin, Cyanide, Arsenic, Asbestos, etc.) and many synthetic ones that are relatively benign in comparison. In summary: Organic does not mean pesticide free, and natural/naturally derived does not mean safe.
For any of us that have taken a toxicology class, one of the most memorable take home messages was “The dose makes the poison”. Credited to a Swiss physician named Paracelsus in 1538, this statement applies to any chemicals (including water, salt, oxygen, caffeine, Aspirin, etc.) that are consumed or absorbed by us, forming the foundation of health and safety guidelines that determine the maximum allowable concentrations (tolerance levels) of these substances in our food, water, and the environment.
One of the most useful and illuminating courses I have ever taken in my career was Environmental Risk Assessment, which covered important topics including toxicology, pesticide risks, and invasive species (among other concepts). This course also detailed how Risk Assessments are conducted, the rigorous regulatory processes and evaluations required before products are even available for use, and the evidence-based tools used to determine whether a substance is hazardous and at what level (dose). A great summary of the Risk Analyses pertaining to pesticides and food safety have been summarized by Alejandro Fernández, Agronomist and Director of Hygiene and Safety of Products of Plant Origin SENASA (Argentine Food Safety and Quality Service), on the Pesticide Facts website (link in resources). These Risk Assessments and Analyses are the foundation of how we go about making determinations regarding any substances that we may be exposed to (including food and medicine).
The Issues with the ‘Dirty Dozen’
One of the biggest issues with the Dirty Dozen list is the fact that they do not communicate what having the highest (and lowest) pesticide residue levels even means. They do not conduct an accurate Risk Assessment to be able to support their message for avoiding conventional produce on this list. Although they do talk about the hazards (substances that have a potential to cause harm to us), they omit the crucial component of actual risk (likelihood of that substance causing harm to us), which incorporates another critical component of Risk Assessments: Exposure (how much of the hazard we are exposed to over a given period of time). If we looked at actual risk from the residues (incorporating hazard and exposure) we would find that the residues found on these produce items on the Dirty Dozen list are extremely low, and far below the threshold of having any risk associated with them, especially if we account for exposure (how many we consume on a daily basis, and over an extended period of time). A peer-reviewed Risk Assessment on pesticide residues published in the Journal of Toxicology by Winter and Katz (2011) in response to EWG’s 2010 Dirty Dozen list found just that (link in resources). Their conclusions were: (1) exposures to commonly detected pesticides in the 12 Dirty Dozen commodities had negligible risks for consumers, (2) substituting organic commodities for these conventionally grown ones did not result in any significant reduction of risk, (3) the EWG methodology for determining risk of these 12 products lacks scientific credibility (Winter and Katz, 2011).
Based on this cool pesticide residue calculator (link in resources), a woman of average height and weight could consume 774 servings of spinach or 453 servings of strawberries (the #1 and #2 produce items on the Dirty Dozen list) in a day without any effects. This calculator utilizes the highest possible amount of pesticide residue recorded by the USDA in these produce items, and not the average amount. Now I don’t know about you, but I would personally struggle to consume even 10 cups of strawberries in a day (every day), let alone over 450 cups. This is a great illustration of how dose/risk works, and why these produce items are considered safe for human consumption in conventional agriculture.
In summary: the EWG fails to mention that these residue levels are still safe, and far below the thresholds that can begin to have an impact on the consumer. This can have negative ramifications for farmers that grow the produce on these lists, especially if they grow conventionally as opposed to organically. Concerns that people may opt to avoid conventionally grown produce, or avoid those specific produce items altogether is an added hurdle for growers to worry about. Both conventional and organic farmers care about what they produce, and also want our food to be safe (for their families and ours). Our regulatory processes further monitor this safety in both conventional and organic production systems, and as the science is updated, so are these processes. Although many lack access to this, if you have access: reach out to local growers and get to know what their practices are to get a better understanding, and support local farmers when possible.
Furthermore, marketing and messaging like EWG’s Dirty Dozen list discourages people from consuming certain produce, and with only 1 in 10 Americans eating enough fruits and vegetables in their diet, the cons far outweigh the pros for this messaging. An article from the Alliance of Food and Farming details some of these negative impacts (see Resources). This type of fear-mongering disproportionately impacts consumers in lower income brackets, and those that lack access to certain produce. A 2016 consumer survey showed 15% of lower income shoppers surveyed would opt to eat less fruits and vegetables after hearing about the ‘Dirty Dozen’ (Huang et al., 2016).
The take home message should be: the produce that you purchase, whether conventional or organic, is safe to be consumed (and backed by rigorous testing that determines this). Do not be deterred from eating the produce of your choice. Choose produce that is enjoyable, affordable, and accessible to you. And whether conventional, organic, or home-grown: eat more fruits and veggies!
Carl K. Winter and Josh M. Katz, 2011. Dietary exposure to pesticide residues from commodities alleged to contain the highest contamination levels. Journal of Toxicology, Article ID 589674, doi:10.1155/2011/589674. https://pmc.ncbi.nlm.nih.gov/articles/PMC3135239/
You’ve probably seen Neem oil recommended in blogs, gardening forums, and on the shelf at your local gardening store. Neem is derived from the seeds of the Azadirachta indica tree, and is one type of horticultural oil that is used by gardeners looking for alternatives to synthetic insecticides. But is it effective? Is it benign? This post explores the pros and cons behind neem and other horticultural oils.
What Are Horticultural Oils?
Horticultural oils are either plant-based (like neem, canola, or clove oil) or mineral-based (refined petroleum products), and they work mostly by smothering soft-bodied pests like aphids, scale, and whiteflies.
Some plant-based oils do contain chemical compounds that can do more than smoother —neem oil contains azadirachtin, which disrupts insect development and feeding behavior.
Horticultural oils are typically considered low-toxicity for humans, and can be used on a very wide range of plants, including vegetables, fruits, ornamentals, and houseplants.
The PROS
Broad-Spectrum Neem oil is effective against a range of insect pests and some fungal diseases, yet remains relatively safe for humans, pets, and other animals. According to the Environmental Protection Agency neem oil “has been shown to have minimal impact on non-target organisms” (EPA, 2012) such as birds and mammals.
Reduced Resistance Potential Unlike synthetic insecticides that often target a specific physiological pathway (and thus promote resistance over time), neem oil affects multiple aspects of insect development, which makes resistance less likely to develop quickly.
Organic-compatible and easy-to-apply Neem and other horticultural oils are generally approved for organic gardening. interventions. They are easy for home gardeners to use since you can spray from a store-bought bottle and avoid any special equipment.
Low Residual Activity These oils break down quickly in sunlight and soil, reducing long-term environmental contamination and residue on edible crops.
The Cons
Phytotoxicity Risk If you use oils in high temperature or direct sunlight, it can lead to leaf burn and plant damage. Apply it early in the morning or late in the day to minimize this risk.
Non-Selective Action Neem and other oils can still harm beneficial insects if sprayed directly. Lady beetles, lacewings, and bees can be affected by fresh residues. You can time your application to avoid flowering periods, or spray during the evening when bees are less active to avoid non-target impacts.
Repeat applications sometimes required The effects of oils can take days to manifest and may require repeated applications (e.g. every 10 days) for best results. Gardeners expecting immediate eradication may be disappointed. Oils often work best in conjuction with other control strategies (e.g. pruning out infested areas, releasing beneficials, etc.)
Storage and Shelf Life Oils can degrade over time, especially when exposed to light and heat. They can go rancid or lose efficaciousness. Check the expiration date on your bottle and store in a cool, dark place.
Concluding Thoughts
I like horticultural oils. They can be effective tools and are safe for people to use. But they need to be used with some consideration, particularly timing to avoid non-target impacts to beneficial insects and leaf burn. Let me know your experience with oils.
Have you ever stopped while you were gardening to look at the clouds? Clouds, like flowers, come in a variety of shapes and sizes that can form beautiful patterns in the sky. But clouds are not just pretty, they can also be used to make predictions about the weather in the coming days. In this week’s post, we will look at the different types of clouds and how they relate to coming weather. You can use that to prepare for your garden work by knowing when it will be sunny and predicting when rain is coming.
Clouds were first classified by Luke Howard in 1803 in his “Essay of the Modifications of Clouds”. Howard classified the clouds by their shape, using Latin names for wisps (cirrus), lumps (cumulus), or sheets (stratus) to describe how they looked in the sky. Clouds that are precipitating either rain or snow are called nimbus clouds. Some clouds are a combination of types, such as stratocumulus clouds, which look like a layer of lumpy clouds, or cumulonimbus clouds, which are the tall thunderstorms that form in summer. You can find a great gallery of cloud photos at the Cloud Appreciation Society. Wikipedia has an exhaustive list of cloud types online as well.
Clouds are also classified by heights. Most clouds form in a single layer of the atmosphere, but you can often see multiple layers of clouds when you look at the sky. These layers may be caused by different mechanisms. The shape and height of the clouds provide clues to what is going on in the atmosphere and are especially related to the presence (and sometimes absence) of warm and cold fronts that are harbingers of precipitation and a change in wind and temperature conditions.
There are many different types of clouds, each with a unique shape and location in the sky. UCAR/L.S. Gardiner
To estimate how high the clouds are, you can use a literal “rule of thumb” that works well for cumulus-type clouds. Hold your hand out towards a cloud. If the individual cloud is the size of your fist, then it is probably a low cloud. If the lump of cloud is the size of your thumb, then it is probably a mid-level cloud. And if it is the size of your little pinky joint, then it is probably a high cloud. Note that the clouds are the same size, but the difference in height makes them look like they are different sizes.
For stratus clouds, you can estimate the height by how transparent it is. A cloud layer that allows you to clearly see where the sun or moon is located is probably a high cloud. A layer that lets you see where the sun is but shows it with blurry edges (we sometimes call this a “ground glass” appearance), then it is probably a mid-level cloud. If it is so thick that you cannot see where the sun or moon is, then it is probably a low-level cloud. But please be careful not to look directly at the sun, since it can damage your eyes!
How do clouds form?
Clouds form where moist air cools off to the point that the water vapor condenses into small drops that become visible to us. Since the atmosphere generally cools off as you go up, the clouds form where the air is rising. The rising motion can be provided by heating from the earth’s surface, lifting of the air by a mountain, or large-scale upward motion caused by warm and cold fronts, where masses of air at different temperatures interact to create areas of rising air. The highest clouds usually form in the coldest air and form as ice crystals, leading to their wispy appearance. Lower clouds appear in warmer air where the water condenses as liquid droplets, leading to their more robust appearance.
Clouds associated with cold and warm fronts, U. K. Met Office.
How are cloud shapes related to atmospheric winds and structure?
The most interesting weather (at least to me, as a meteorologist) is where there are differences between masses of air at the surface and above the surface that are interacting. Boundaries between these air masses are called “fronts” and are named because they act like battle fronts between enemy armies. In a cold front (left side of diagram above), cold dense air near the surface pushes beneath a layer of warm, humid air, causing it to rise and cool. Clouds ahead of cold fronts tend to be relatively tall and energetic and form cumulonimbus clouds that can drop a lot of rain in a short time but generally tend to move through an area quickly unless the front stalls due to other atmospheric dynamics.
Warm fronts are large masses of warm, humid air that are pushing over the top of a layer of colder, more dense air (right side of diagram above). As the warm air rises, it slowly forms clouds as the layer cools to the temperature of condensation. Since the entire layer is rising, the clouds that form are often sheets of clouds rather than individual clouds. The higher clouds indicate that the moisture from an approaching warm front is present high in the atmosphere and shows that a warm front is likely to be approaching, signaling a change in the weather from cool to warmer conditions that could also drop rain as the warm front gets closer to your location. As the warm front gets closer, you should see the high clouds replaced by mid-level clouds like altostratus and then lower clouds like stratus clouds and nimbus clouds if they start producing rain. This usually happens over a day or two depending on the speed and strength of the surface warm front.
If you see lumpy cloud forms, then they are most likely related to the rising motion of air due to columns of warm air rising from the surface (“thermals”). Air between the columns is sinking, which leaves clear spots between the clouds. Fair-weather cumulus clouds are the tops of these thermals, when the rising air cools down enough for the water vapor in the column to condense, forming the cloud. These types of clouds usually form when the ground is heated, most often by sunlight during the day but sometimes by pavement or wildfire as well as mountainous areas. They usually form on days when you are in a mass of warm, humid air that is far from a frontal boundary, although if they grow taller, then a cold front is likely to be approaching.
If the air is very hot and humid and the surrounding air is cooler than the rising column, then the clouds can grow vertically to great heights before they hit a layer that is warmer than the rising air and stop growing. These tall clouds are called cumulonimbus clouds because they often drop heavy rain as they develop. These often form along and ahead of cold fronts and indicate that the wind is likely to shift from a south wind to a colder wind coming from the northwest (in the Northern Hemisphere). In the worst cases, the rain can cause erosion or damage to fragile plants when it is very intense. Plants that live in rainy areas evolve to have such things as pointed tips or shiny leaf surfaces that shed the water quickly. Cumulonimbus clouds are also sometimes associated with high winds, hail, and tornadoes, all of which can damage garden plants and trees as well as harm humans and animals.
Cirrostratus clouds being illuminated by the sun and forming a halo, Eduardo Marquetti, Commons Wikimedia.
How can you predict the weather by watching the clouds?
As you work in your garden, take a look at the clouds above you. If they are high and wispy, then moisture high in the atmosphere may indicate that a warm front and a chance of rain is likely in a couple of days, especially if they get lower and denser over time. The picture of daisies at the beginning of this post shows high, wispy clouds that could indicate a warm front is approaching. The glowing ring of light that appears in cirrostratus clouds in the picture just above this paragraph may also be a sign that there is moisture on the way, leading to the saying that “a ring around the moon means rain in 48 hours”.
The chance of rain may affect your plans to spray your gardens or lawns for pests or fungal diseases, since many garden treatments have weather-related requirements for when to use them. Some work better when applied to wet leaves after rain falls, but others need a period of dry weather for the chemicals to be most effective. Make sure you read the labels to know what kind of weather they need. It may also tell you that it would be a good idea to mow the grass before it rains in the next 24-48 hours.
An Intercity from Amsterdam to Den Helder passes a field in full bloom near Schagen, Netherlands, Kabelleger / David Gubler, Commons Wikimedia.
If you are already in hot and humid conditions and you see cumulus clouds getting taller and more numerous over time, a cold front may be approaching. This could indicate a period of strong winds, heavy rain, some possible lightning, and sharply cooler temperatures which could be either a curse or a blessing depending on just how hot it has been. The very shallow clouds in the picture above (cumulus humilis) are most likely seen after the cold front has passed and there is minimal lifting to cause clouds to form.
Don’t forget to look up
A good gardener should always be keeping an eye on their garden but should also be watching the environment around it to see how the conditions might be changing in the future. Who knows what delights you will see if you just look around you? But don’t forget to look up, too, because the sky is full of wonders and can inform you about the future as well as strike you with awe.
Bee hotels have become popular additions to gardens, designed to support wild bees by providing them with nesting sites. Solitary bees, unlike honey bees, live in natural and man-made cavities which can be easily provided with nesting habitats. A previously published Garden Professors blog offers valuable insights into creating artificial nesting structures for these bees, emphasizing the importance of proper design and placement. However, if you’re thinking about installing a bee hotel, I’d urge you to reconsider – some studies suggest that bee hotels, if not correctly maintained, can inadvertently harm the very pollinators they’re meant to help.
While bee hotels offer nesting opportunities, there is almost no research showing that they have a positive effect on bees. Some researchers also think bee hotels can become hotspots for parasites and pathogens (MacIvor & Packer 2015). High-density nesting sites can facilitate the spread of diseases, similar to how bird feeders can become transmission points for avian illnesses. Bees are particularly vulnerable to viruses, microsporidians, and fungal agents which can spread via exposure to feces or even through pollen left behind by bee visitors. Bee hotels can also attract bee predators – nesting aggregations of wild bees that are artificially close together might be attractive to parasitic wasps which infiltrate nests, laying their eggs inside and jeopardizing the bee larvae.
Bee hotels may still have their place, especially in community gardens where they can serve as a point of conversation and provide beauty and interest as a form of garden art. However, given the risk for disease spread, here are some tips for maintaining a bee hotel.
Best Practices for Bee Hotel Maintenance
To ensure bee hotels remain beneficial:
Annual Cleaning: After bees have emerged in the spring, clean the hotel thoroughly. Remove and replace any natural reeds or paper straws. For wooden blocks, use a thin bottle brush or compressed air to clean out debris.
Use Removable Nesting Materials: Opt for bee hotels with removable tubes or liners. This design facilitates easier cleaning and reduces the risk of disease buildup.
Proper Design: Ensure that nesting holes are closed at one end to prevent parasites from accessing the nests from behind.
Limit Nest Density: Avoid overcrowding by limiting the number of nesting tubes. A lower density reduces the chances of disease and parasite spread
Create Habitat: Leave undisturbed, unmulched areas in the borders and corners of your garden so that bees can nest naturally in the ground. Some bees also nest in dead twigs and hollow stems and branches, so consider leaving some behind for them.
Do you have a bee hotel in your garden? What has been your experience with them?
References:
MacIvor, J. S., & Packer, L. (2015). ‘Bee hotels’ as tools for native pollinator conservation: a premature verdict?. PloS one, 10(3), e0122126.
If you’ve been paying attention to the weather across the United States this past week, you may have noticed that most of the eastern U. S. is experiencing extremely hot temperatures, especially when you factor in the effects of humidity. At the same time, in the western U. S., it has been snowing in the mountains, even though it is almost July! In this week’s blog post we will look at why this pattern of hot and cold conditions occurs so often and what is causing it.
Mount Timpanogos with wild flowers (Utah, USA), Taken on 28 August 2011, Brian Smith, Commons Wikimedia.
Heat in the East
We have talked about persistent areas of very high temperatures several times in past blog posts (for example, here and here). Those areas most commonly form in summer under stagnant areas of high pressure that have sinking motion in the middle of the high. The sinking motion of the air keeps clouds and rain from developing, leading to very hot and dry air being trapped near the earth’s surface, raising temperatures and reducing wind speeds. Often those areas also include a lot of humidity, which makes the temperatures more oppressive because sweating does not cool you off efficiently if the humidity is high, especially if winds are also light.
Formation of a heat wave : a high-pressure circulation in the atmosphere acts like a dome or cap, trapping heat at the surface, National Ocean Service, NOAA.
It is also interesting to note that in winter, areas of high pressure are often the coldest areas of the country due to the lack of cloud cover, which allows heat from the earth to escape to space, leaving colder conditions at the surface at night when no sun is there to heat the ground.
Texel – De Hors – One of the heat wave days of the Summer of 2008 – At the South Beach Corner of Marsdiep & North Sea, Txllxt TxllxT, Commons Wikimedia.
The common connection between the heat in the East and the snow in the West is the large-scale atmospheric wave that is linked to both the low pressure in the west and the high pressure in the East. The atmosphere is a fluid and is constantly adjusting its pressure fields by forming waves with ridges of high pressure as well as troughs of low pressure. Sometimes these patterns get locked in place for a few days (or even longer in rare cases), which leads to more extreme effects, but they usually move on in a few days, causing the weather to go back to normal conditions or even flip-flopping to the opposite pattern. In fact, we discussed atmospheric waves back in July 2021 following the PNW extreme heat event in this blog.
The surface weather associated with these areas of high and low pressure are what cause the big changes in observed conditions that gardeners and farmers have to deal with since they can have big impacts on flowers and crops. The atmospheric wave pattern can lock in place for a number of reasons including conditions in other parts of the earth such as unusually cold or warm water in the ocean or droughts or floods in other areas. Fortunately, these stationary patterns usually shift or break down after a few days, leading to big changes in local weather conditions that might be more welcome.
Cold spells in summer do not cause as much damage as frost and snow in spring and fall because they just don’t get cold enough to damage the plants (unless you are in the mountains and the temperatures drop below freezing), but they can slow the plants’ growth and reduce their flower or fruit production. Food crops that depend on a significant number of growing degree days (a measure of the accumulation of heat over time based on daily temperatures) will grow more slowly, resulting in late harvest of whatever crop is being grown. In the worst cases, it could delay harvest so late in fall that fall frosts become a consideration, but most home gardeners do not need to worry about this as much as commercial farmers because they are not farming hundreds of acres of crops, just their own patch of land.
I encourage you to visit some of the links in the article above to learn more about heat domes and atmospheric waves as well as their impact on your garden plants. You can also use the search field to find additional sources of information about any topic of gardening that you might want to learn more about, especially one that relates to the science of gardening. It’s a great resource!
残雪とエゾツガザクラ（Snow and flowers), pakku, taken on 31 July 2009, Commons Wikimedia.
I wish I could say I grew up with an innate fascination for the insect world—that I was one of those kids who spent hours flipping over rocks to marvel at beetles and ants. But the truth is, growing up in urban Los Angeles, I rarely interacted with nature at all. And insects? I was terrified of them. I was the last person to volunteer for anything involving creepy crawlies.
That all changed in college. I enrolled in an introductory environmental science class, and one guest lecture changed the course of my life. A campus professor gave a talk on agroecology, describing how their work wove together science, practice, and social movements to promote sustainable pest management. I was captivated. Here was a discipline that tackled food production, ecological health, and community well-being—all at once. It felt like a bold, grounded approach to conservation—not one that isolates nature in national parks, but one that weaves ecological thinking into everyday landscapes like farms and gardens.
I emailed him that very day, requesting an internship—and he agreed. My first day on the job found me in a vineyard in the Central Valley, shaking grapevines over a beating sheet, pretending I wasn’t afraid as a swarm of insects fell onto the canvas. The graduate students in the lab patiently taught me how to tell wasps from bees, bugs from beetles, and moths from butterflies. They also introduced me to the foundational concepts of biological and cultural control—how pests can be managed using natural enemies and sustainable farming practices. Later that year, one of those graduate students asked if I’d be willing to host one of his beehives in my backyard. I instantly fell in love with those bees—their complex, maternal society, their admirable work either, and the delicious honey they produced. That hive sealed it for me: I was going to become an entomologist.
After graduating, I apprenticed at the UC Santa Cruz Center for Agroecology and Sustainable Food Systems, where I sharpened my skills in horticulture, including irrigation, nutrient management, composting, greenhouse production, and pest management. I worked across a diverse range of crops, from annual vegetables to ornamentals and perennial fruit trees. During my Ph.D. and postdoctoral work, I focused on how farm and garden management practices influence wild bees and their susceptibility to the parasites and pathogens implicated in pollinator declines. My research sits at the intersection of agriculture and ecology, and I’ve always believed that productive farming and environmental stewardship should go hand in hand.
Now, I serve as an Extension Advisor with the University of California, based in Ventura County. As an entomologist, my primarily focus is on integrated pest management of insect pests, including identification and monitoring, developing cultural and biological control methods, and evaluating new chemical control products. One of the best parts of my job is the incredible variety of crops I get to work with, including avocado, citrus, strawberries, cole crops, and greenhouse ornamentals – working with so many different commodities means that I’m constantly learning. In my work I aim to provide science-based, practical recommendations that help farmers, pest control advisors, and others in the industry to effectively manage pests while safeguarding beneficial insects and human health. For example, I’m currently leading several projects that explore how small-scale habitat enhancements—like hedgerows or cover crops—can improve pest control and support wild pollinators in citrus orchards.
I didn’t set out to become an entomologist. But through a mix of chance, community, and unexpected inspiration, I’ve found myself surrounded by insects—not in fear, but in deep fascination and appreciation.
I am traveling in Colorado this week, so my thoughts naturally turned towards the mountains. Mountains affect gardening in a number of ways, many of which include a weather or climate component. They also provide some special challenges for gardeners because of the harsh conditions and short growing seasons that are often found in and near mountainous terrain.
Red Rocks Park in Autumn, MichaelKirsh, Commons Wikimedia.
How the mountains affect weather and climate
It is said that mountains create their own weather, and there is a lot of truth to that. Mountains interact with the atmosphere in several ways, and that interaction can change both the atmosphere itself and the conditions on the surface of the mountain that is being affected by the air.
If the air is diverted sideways around the mountain it can block the wind from hitting some locations downwind of the peak. Our fearless leader Linda told me she experienced this just a few weeks ago when a strong low-pressure center moved into the Northwest, bringing strong winds to the region. However, Linda noted that in her location, those winds were blocked by Mount Rainier, resulting in much lower local wind speeds due to the shelter from the massive mountain.
Wind flow up and down the mountains due to temperature variations
Mountains can heat or cool the air around them, depending on the time of day and the season. In summer, the peaks warm up and provide a heat source that helps lead to the formation of thunderstorms. You can see this almost every summer day in the western US with storms that develop over the mountains as the sun warms them. Those storms then move out over the prairies, leading to scattered rain or even virga, rain that evaporates before it falls to the ground. At night or in winter, the air near the peaks cools quickly and the denser air flows down the mountains into the valleys, resulting in katabatic winds that can cause freezes in low-lying areas when the coldest air reaches the lowest elevations. In this situation, the valley floors may experience frosts while areas on the slopes remain above freezing because the dense air drains through them relatively quickly. The winds can also increase evaporation rates, limiting the amount of available moisture and causing water stress on garden plants.
Orographic rainfall diagram, Encyclopedia Brittanica, Inc.
Temperature variation with elevation and orientation
The surrounding atmosphere also affects conditions on the mountain terrain. Atmospheric temperatures decrease with height, so as you go up in elevation on a mountain, the temperature will drop. This can lead to cooler climates and shorter growing seasons due to the increased likelihood of frost with the colder temperatures. This limits the types of plants that gardeners can grow because the climate of that location has limited suitability for plants that grow well on the flatlands.
Another aspect of mountainous terrain is the number of microclimates that are present in the rocky, uneven landscape. Mountaintops and sides offer a range of microclimates, from sunny, well-drained slopes to shady, cooler areas, influencing plant growth in different locations. North-facing slopes get little direct sunlight and can pool pockets of cold air that result in frosts every month of the year, while sunny south-facing slopes could be much warmer and more suitable for a variety of plants. Any mountain gardener has to be especially aware of the local microclimates in their area and account for them when choosing what and when to plant.
Alpine garden, Montreal Botanical Garden, Thomas1313, Commons Wikimedia.
Of course, there are other characteristics of mountains that can also affect garden success. Soils are often shallow, rocky, and low in organic matter. Lower pressure and humidity may cause problems with plants’ ability to thrive in the harsher conditions. Sunlight can be very intense and shade from taller plants may be limited. Some areas may experience extensive periods of snow, which can provide insulation but can also damage plants when it slides downslope.
Gardening in the mountains can provide challenges for many gardeners due to the difficult environment that the mountain air provides, but it can also allow gardeners to create unique collections of alpine vegetation that can provide enjoyment for years to come, all set in a diverse and scenic landscape. Be sure to look for additional information on alpine or mountain gardening on the web to make sure your garden is well-suited to your local conditions.
Alpinarium w Bydgoszczy, Pit1233, Commons Wikimedia
Deciphering fact from fiction for one of the most infamous plants in the world.
Dandelion in a lawn. Photo: Abiya Saeed
Dandelions can be a bit of a polarizing subject for gardeners. Some absolutely love them, while others may despise seeing these bright yellow bursts of unconformity in an otherwise ‘pristine’ lawn and garden landscape. Many often find themselves somewhere in the middle of this spectrum. Dandelions are also used as a symbol for resilience–growing despite all odds in some very harsh and unforgiving environments–often ones where few cultivated plants would successfully grow. Some people enjoy eating them, while others embrace them as a source of nectar, pollen, and food for other critters in the landscape. There is a lot of wonder in the way that they disperse, and many kids and adults alike have enjoyed blowing on dandelion seed heads (with or without making a wish) to watch them float away in the wind, drifting to new locations that they can conquer as their own. There is even an annual festival devoted to dandelions in Carbondale, Colorado (located in the same county where I served as an Extension Agent several years ago). When I attended years ago, it was such a cute and unique event, where people were wearing dandelion flower crowns, sharing art and artisan products associated with dandelions, and enjoying music and merriment in the spirit of the whimsical yellow plant. There is a lot of myth, magic, and majesty associated with dandelions, that it can be hard to decipher fact from fiction.
I get asked about dandelions more than any other plant combined– especially pertaining to pollinators, but also many other things. These queries come from people of all backgrounds and viewpoints, ranging from: how to get rid of them, to: how one can encourage and/or intentionally grow and cultivate them. These queries are especially common as spring rolls into Montana with the classic yellow bursts of color being some of the most visible flowers at this time of year, especially in the colder climates of zone 4 in the greater Rocky Mountain region. I have found myself endlessly poring over research to try and answer some of those questions, that I thought it would be fun to ‘dig in’ (pun always intended) to the lore of dandelions and the science-based information that we have on this notorious plant.
The Dandelion
Dandelions (Genus: Taraxacum) are a widespread genus in the Aster family that can be found in most parts of the world, either as a native plant or naturalized through intentional and unintentional introductions. Although there are around 250 species in the genus, the most widespread dandelion species is Taraxicum officinale, also known as the ‘common dandelion’, which originates from Eurasia but is now naturalized in many parts of the world (and can be found on on every continent except Antarctica). For the purposes of this Blog post, I will be focusing on information pertaining to the common dandelion (Taraxicum officinale). This is considered a short-lived perennial plant that can reproduce sexually (through seeds) and asexually (through the roots), can withstand a wide variety of climates and soil conditions, all of which can contribute to the fact that dandelions are so prolific and widespread.
Starting out as a rosette of lance-shaped leaves, it shoots up the characteristic yellow flowers in early spring. Each ‘flower’ is actually an inflorescence that consists of several ray and disc florets clustered together (similar to its relative: the sunflower). The length of the flower stalk is extremely variable, ranging from a couple of inches (in frequently mowed areas such as lawns) to multiple feet in length. I once saw a dandelion curiously poking out through the top of a boxwood shrub that was nearly 3 feet tall, and upon investigation, measured the stalk at a staggering 35 inches (which is half the length of the tallest dandelion stalk on record found in Ontario, Canada). The flowers are followed by the very distinct seed-heads which contain individual seeds, each of which are attached to a fine tuft of hairs (a pappus) that act as a parachute to aid in wind dispersal. Dandelions are well-known for their tap-root which can contribute to the plant’s drought tolerance, and allows them to compete well with other vegetation for limited resources.
The fact that dandelions are edible is not a topic that is frequently debated. Many know this to be true. Almost every part of the common dandelion from the taproot to the flower heads is all edible (with the exception being the stems which contain a milky latex that can be very bitter). Plenty of dandelion recipes can be found with a quick Google search. There is, however, much debate about their taste. To some, dandelions are a whimsical treat, where you may enjoy the flowers or young leaves in a salad, while others choose to steep parts of the plant to make teas, or enjoy the fermented products as delectable dandelion wines. Furthermore, dandelions can be found in many skincare products, salves, lotions, herbal remedies, and more.
In North America, European settlers intentionally brought dandelions for their nutritional and medicinal value. They were intentionally grown alongside vegetable and herb plantings, and used to remedy a variety of ailments. The nutritious properties of dandelions are comparable to salad greens such as spinach and arugula. Leaves are high in potassium, calcium, and iron, whereas the roots can have diuretic and laxative properties. For more information on dandelions as food, check out the link to the publication from University of Wisconsin in the resources.
Although I have yet to find a dandelion recipe that I thoroughly enjoy (besides recipes that try and mask the flavors using in intense array of herbs and spices, or baking them into treats, brewing them into teas, and fermenting them into wines). I am not personally a fan of the bitter and earthy flavor of the raw plant, though I admit, I haven’t tried all variations of cooking or flavoring the parts of a dandelion. If you have a recipe you love and swear by, feel free to share it with me, and I will give it a try (as long as it isn’t too time and resource intensive). Regardless of your taste preferences, if you do choose to eat dandelions, collect them from a safe location, make sure that they have not been treated with any chemicals, and wash them thoroughly to remove any soil, debris, or insects.
Dandelions and Pollinators
Many embrace dandelions because of the associated value to pollinators. The science behind this, however, is not as black and white as some may think. Although dandelions can be convenient sources of pollen and nectar for pollinators in highly urbanized landscapes, especially early in the season when very few other plants may be flowering in some of these densely populated areas, they are not the highest quality source of food for many of our pollinators. Some claim that dandelions are the earliest flowering plants blooming in the spring, which is also untrue in many parts of the world. That being said, dandelions are among the most widespread and consistent sources of nectar and pollen in some landscapes (such as urban areas with fewer flowering plants intentionally incorporated to support pollinators all season long) and also some of the earliest blooming plants visible in these types of landscapes.
A lot of research has been done that shows dandelions attract a wide array of pollinator species, and can therefore be a critical source of food for pollinators in urban areas, where these plants are widespread and can act to bridge the gaps between other areas of more diverse floral resources (Larson et al., 2014). Research also shows that dandelions do not have the most nutritious nectar and pollen, lacking in certain important amino acids, making pollinators (such as honey bees) unable to survive on dandelions alone (Loper and Cohen, 1987). We also know that a dandelion-only diet can impact the ability of honey bees to rear brood (Herbert et al., 1970). Unfortunately, our research is usually restricted to managed bee species such as honey bees, so we have far less information on how most of our pollinator species (including the rest of our 20,000 species of bees) would respond to a dandelion-focused diet. What we do know is that pollinators need a varied diet with floral resources available all season long, including early and late in the growing season when some nectar and pollen collecting species have to begin provisioning their nests and when some species are getting ready to overwinter. Although there are countless flowering plants that are better for supporting pollinators, dandelions will always have a place on that list until more intentional pollinator-friendly plantings are incorporated.
Dandelions can also support caterpillars of a variety of butterfly and moth species. These caterpillars will use the rosette of leaves produced by dandelions as their primary source of food, or as part of a wider diet consisting of a variety of plants. These caterpillars, in turn, can be an important source of food for animals higher up on the food chain (including birds). This can make dandelions important for ecosystems beyond just their nectar and pollen for pollinators.
Dandelions as a Weed
Common dandelions are undoubtedly a resilient plant in many landscapes, as all of us have seen them popping up in lawns, through dense vegetation, in gravel roads and driveways, sidewalks, roadsides, and so on. In fact, it would be difficult to imagine a landscape without dandelions. Because they can grow in conditions that may not favor some other cultivated plants, and therefore may be found taking over areas where you wanted to grow something else, they are commonly considered a weed. In fact, they are probably the most famous weed you can think of, and the poster plant for many lawn care companies, herbicides, and other garden products aimed at controlling or limiting their abundance in our managed landscapes.
Some research shows that dandelions can compete with native vegetation for resources. Research in Japan on native Taraxacum spp. and the impact of growing alongside Taraxicum officinale showed a reduction in seed production for the native species (Kandori et al., 2009). The authors hypothesized that the more attractive flowers of T. officinale may deprive the native species of pollinators, resulting in a reduction of pollination services. They also stated that the transfer of pollen from the non-native species could interfere with the successful reproduction of the native species, however, this was disproven by hand-pollination experiments (Kyogoku, 2021).
In many home garden settings, whether or not something is a weed, is usually very subjective and dandelions are no exception. I, personally, don’t mind dandelions growing opportunistically in certain managed landscapes (though seeing non-native dandelions in natural ecosystems is an entirely different story). My stance on many persistent (non-noxious) weeds in the garden is usually a variation of ‘may the best plant win’, but I know that not everyone feels this way. Although some embrace the odd dandelion speckled in a lawn, when you have large swaths of dandelions in the place of what used to be turfgrass, the problem usually extends beyond dandelions themselves.
One of the best ways to combat dandelions in a turf lawn setting, is to make sure that your turfgrass is healthy and able to form dense coverage on the soil. Healthy turf can often outcompete weedy vegetation that can opportunistically take advantage of open spaces for establishment. Addressing soil compaction, nutrient needs, and responsibly caring for your turf lawns can all play a role in reducing weed issues, including dandelions. For situations where competing vegetation may not be an option, mulches can be used to reduce the presence of dandelions that may be found in flower beds or veggie gardens. Mechanical removal is also very effective for controlling dandelions, depending on the scale of the issue. Using your favorite tap-root removal tool (such as the aptly named dandelion fork) can remove plants without too much exertion. Pulling out as much of the root as possible will offer the best control, as dandelions are less likely to propagate from smaller root fragments.
Several herbicide options are also available for dandelion control. Broadleaf herbicides such as 2,4-D, dicamba, and MCPP (commonly found in ‘weed and feed’ fertilizer products) can be effective for dandelion control in lawn settings. Spot-treating individual plants using an appropriately labeled broadleaf weed killer is usually more effective than broadcast application across larger areas. Herbicides with the active ingredient Glyphosate are not as effective for long-term control of perennial weeds like dandelions, because they often knock back leaves without killing the roots, which allows the plants to regenerate. These products can be more effective if a plant is cut or mowed and the herbicide is carefully painted on the fresh cut, which can facilitate movement into the root system. Late summer and early fall is the best time to control perennial weeds such as dandelions. This is because these plants are moving resources from the foliage to the root system in order to prepare for winter, which can also help to transport systemic herbicides to their roots and/or deplete their root systems of energy for more effective and longer-lasting control. (Remember that herbicides may kill desirable plants, and not just weeds- so use them responsibly and sparingly while taking precautions not to apply them near susceptible plants). Always, always, always read and follow label directions, and if unsure: reach out to your Extension resources for assistance.
Whether you are a big fan of dandelions, or the opposite of that–I hope that you learned something new from this post–and continue to be curious about the plants that surround us!
Larson, J. L., Kesheimer, A. J., & Potter, D. A. (2014). Pollinator assemblages on dandelions and white clover in urban and suburban lawns. Journal of Insect Conservation, 18, 863-873. https://link.springer.com/article/10.1007/s10841-014-9694-9
Herbert, E. W., Bickley, W. E., & Shimanuki, H. (1970). The brood-rearing capability of caged honey bees fed dandelion and mixed pollen diets. Journal of Economic Entomology, 63(1), 215-218. https://academic.oup.com/jee/article-abstract/63/1/215/798721
Kandori, I., Hirao, T., Matsunaga, S., & Kurosaki, T. (2009). An invasive dandelion unilaterally reduces the reproduction of a native congener through competition for pollination. Oecologia, 159, 559-569. https://link.springer.com/article/10.1007/s00442-008-1250-4
