The Garden Professors™

 Everyone has their favorite season. Mine is spring, because of the pop of early flowers, the hundreds of shades of green that appear as bushes and trees leaf out, and the warmer temperatures that come with the march towards summer. Winter is my least favorite because of the lack of color after the deciduous trees drop their leaves, leaving stark black branches against white clouds or snow.  I admit I don’t like the cold either! Most of us talk about the seasons a lot, but what are they really? Today’s topic is how seasons are defined and how that relates to gardening.

Definitions of seasons

Seasons can be defined in several ways. The most common definition of a season is the astronomical season. This is related to the movement of the earth around the sun. Since the earth’s axis of rotation is tilted by 23.5 degrees relative to the plane of the earth’s orbit, the amount of sunlight anywhere on earth receives changes depending on whether the pole is tilted towards the sun or away from it. In the Northern Hemisphere, summer begins at the summer solstice, when the North Pole is pointed most directly at the sun. This is when the sun appears highest in the sky at noon, usually around June 21. The winter solstice occurs when the earth is halfway around the sun six months later and the North Pole is pointed most directly away from the sun. This means less energy is reaching that hemisphere, resulting in fewer hours of daylight and less incoming sunlight, resulting in cooler temperatures. Between the two solstices are the vernal (spring) and autumnal (fall) equinoxes, the dates on which the lengths of day and night are basically equal. They fall on roughly March 21 and September 21. As the earth progresses on its orbit around the sun, we cycle through these geometric changes, resulting in the variations of incoming energy that drive the rise and fall of average temperature over the year.

Climatologists and meteorologists define the seasons by date instead of by geometry. Northern Hemisphere winter is considered December, January, and February, spring as March through May, summer as June through August, and fall as September through November. In part, these calendar months were chosen for ease in calculating averages for monthly and seasonal climate reports in the days before calculators were available and all averages were calculated by hand. But it turns out that the calendar months are a better measure of when the warmest and coolest three-month periods occur (climatological summer and winter) than astronomical seasons are. So the seasons change for climatologists several weeks before the astronomical change of the seasons occurs. If you want to learn a lot more about different ways to define seasons climatologically, then I recommend Brian Brettschneider’s detailed article on Defining the Seasons.

Defining seasons by phenology

In addition to astronomical and climatological seasons, there are other ways of defining the seasons as well. One method of measuring the start of a season is through the use of phenology, the study of when a particular environmental event is observed to occur. This could be the first leaf on a honeysuckle bush, the first cherry blossom, or the first date a northern lake is frozen over in winter. Gardeners’ observations are critical in marking the change of seasons using phenology because they carefully watch the plants and animals in their local landscapes over time. The National Phenological Network in the United States is a citizen science effort underway for many years that catalogs the changing seasons by monitoring and recording a variety of phenological events as reported by gardeners and others. Many other countries have similar phenological societies that catalog the first blooms of different trees and flowers as well as changes in rivers and lakes or the appearance of migratory birds like robins for the first time each spring. Maybe some of you contribute to this effort in your own community or country. Some countries like Japan have kept records of first cherry blossoms on particular species of trees for hundreds of years and have seen how this has changed over time. This allows us to see long-term trends in climate based on based on how changes in temperature and precipitation are affecting the way plants grow.

A new phenological index: the Late Bloom Index

While many phenological studies keep track of “first” occurrences like the first cherry blossom or the first leaf on a particular type of tree, the National Phenological Network has recently introduced a new index called the “Late Bloom Index”. This index records the last occurrence in a year of a phenological event such as the last time a bloom is observed on a particular plant species. Keeping track of both the first and last bloom of a plant species gives us a deeper understanding of a plant’s life cycle as well as allowing us to track climate variations through phenology.

The seasons are changing

Use of phenological data has allowed us to study changes in climate in a new way. A recent study of seasons defined by the phenology of different native plants that bloom at different points in the year has shown that the seasons as defined by these plants have changed in Germany (Guido Cioni). According to their research, spring, summer, and autumn (as defined by phenology) are all starting earlier in the calendar year than they did in the past. This might sound odd, but if you think about how plants grow, it makes more sense. Once plants begin their life cycle of producing leaves, blossoms, and fruit, they progress through that life cycle on a regular schedule that is controlled by the climate that plant is growing in as well as by their genes. If spring starts earlier due to the warming climate, then the plant will grow and propagate on its own regular schedule and will finish its life cycle earlier than when the climate was cooler. This has some unfortunate consequences for insects, birds, and other animals that depend on the fruit of particular plants, since they may occur earlier in the year than in the past and that may not match the needs of those animals for migration or preparing for hibernation.

The seasons of your garden

If you don’t already keep a journal of what you are observing in your garden, I encourage you to start. That is a great place to keep track of how your plants (and insects and birds and wildlife) are changing over the year. If you live in the same place for long enough, you will have a historical record of how your local climate is changing and a source of enjoyment at how weather and climate may be impacting your garden’s growth from one year to the next. You may even wish to provide your observations to the NPN using their Nature’s Notebook program. That will allow you to compare your own observations to other gardeners around the country and the world. You can be a scientist as well as a gardener!

How did your garden fare this year? No matter how it grew, at least some of the impact was due to this year’s weather, although careful soil preparation and a good watering plan can fend off some of the worst effects. As usual, my last blog post of the year will be a brief review of this year’s climate and a look ahead to next year. Gardeners must prepare as well as dream! My review will focus heavily on the United States, but I will try to put in a little for our non-US readers too.

How warm was the earth in 2025?

After 2024’s record-setting warmest year on record for the globe, temperatures worldwide in 2025 were not quite as warm as in 2024, although they were certainly warmer than average. While the final average is not yet available, the first eleven months of the year were the second warmest on record, right behind 2024, so 2025 is likely to be in the top three warmest overall, but is not likely to be the warmest ever due to the extra warming from El Niño in the early part of 2024. If you are interested in seeing a time series of temperature for the globe, you can use the “Climate at a Glance” tool from the National Centers for Environmental Information to make your own plots. You can also see more about how El Niño and La Niña affect global climate here and here.

This year’s overall temperature was slightly reduced due to the presence of the La Niña that is currently occurring in the Eastern Pacific Ocean, causing a decrease in the sea surface temperature there (see graph above). As expected, the parts of the globe that are warming the most rapidly are the areas near the Arctic, since the loss of snow cover and sea ice make they warm up much more quickly than other areas with less frequent snowy conditions.

What was the US precipitation pattern like this year?

Again, the year is not quite complete yet, so we will have to wait for final numbers to be tabulated in January. However, using the “Climate at a Glance” tool, we can see there was a lot of variation for the first eleven months of the year in precipitation across the lower 48 states, with some areas like Kentucky and the Ohio River Valley and the Northern Plains receiving much above average rainfall while other areas like parts of the Corn Belt in Indiana and Illinois, Florida and adjacent areas of Alabama and Georgia, and most of the western US receiving much lower than normal rainfall.

Of course, an 11-month total does not describe how rainfall varied across the year, and some places like the Southeast where I live actually started out so wet it was hard for farmers to get out into their fields and ended the year so dry that exceptional drought formed in parts of that region. Since we did not experience any landfalling hurricanes this year and only one tropical storm, there was little impact on the rainfall pattern in the US in 2025, and the lack of rain may have contributed to the drought the developed later in the year in the Southeast due to the lack of tropical rainfall, which often provides a significant fraction of the precipitation in the summer months in areas affected by tropical weather.

What was the US temperature pattern like?

The temperature pattern of anomalies across the United States was less variable than the rainfall pattern and showed that most areas of the country were warmer than normal, especially in the western half of the Lower 48 states. You can find more detail, including maps for Alaska and Hawaii, in NOAA’s National Climate Report. A few areas in the eastern US were cooler than the 1991-2020 average but still above the long-term average. One of the things that struck me this year is how variable the temperature was, with some prolonged heat spells followed by cold outbreaks. This was especially seen in mid-November this year, when a warm start to the fall season was broken by an intense cold front that drove freezing temperatures nearly to the Gulf, ending the growing season in the Southeast earlier than expected in many areas. 

If you like to see satellite imagery of unusual weather or other activity like volcanic eruptions, be sure to check out NOAA’s annual gallery of interesting photos or videos of interesting events seen from the NOAA satellites, including wildfires, dust storms, atmospheric rivers, hurricanes, and even volcanic eruptions, many of which I have discussed in previous blog posts.

What should gardeners expect in 2026?

As of late December, we are currently in a weak La Niña, which means the ocean temperature in the Eastern Pacific Ocean is cooler than normal. That usually affects weather across the US by shifting the most active weather to the northern states, bringing a lot of rain, snow, and very cold weather to those areas while leaving Southern states warmer and drier than usual. But that is only expected to last into the early months of 2026 and after that we will return to neutral conditions. In fact, it is not unlike the conditions we expected last spring, when we were also leaving a weak La Niña and headed back to neutral conditions. Generally, when there is no El Niño or La Niña, the weather can be more variable and we can get more frequent swings between warm and cold conditions. There is likely to be some lingering effects from the La Niña that is currently occurring, so that means we will likely continue to see cold and wet conditions in northern parts of the country while southern areas are likely to be drier, sunnier, and warmer than usual for the next few months. One difference is that this year the predictions are that after several years of La Niña or neutral conditions, we are expected to swing to an El Niño, which will likely cause much different climate impacts next fall and winter than what we observed this year.

Gardeners in southern and eastern areas should be on the lookout for potentially early blooms on fruit trees with the potential for a late frost that could kill off the blossoms. I would say to be cautious in planting your gardens too early because of the potential for cold weather returning after an early warm-up. In northern areas, spring could be late in coming this year. If it stays warm and dry in the Southeast this winter, a spring or early summer drought could occur, so make sure you have a good watering plan in place (of course, that holds true for most gardeners, since a dry spell can happen even in a season that is fairly wet).

How did the weather affect your own garden this year?

I am always interested to hear stories from gardeners about how the weather and climate affected their own gardens. Please feel free to share anything that affected your local conditions, from hail that damaged vegetables or fruit to unusual heat that caused problems with pollination. If your garden had an excellent year due to perfect growing conditions, I would love to hear that too! Be sure to say what state, country, or city you live in so we can compare the climate maps to what you observed.

Thanks for subscribing to “The Garden Professors” and let’s look forward to another interesting and productive garden year in 2026!

If you spend much time on social media, you have probably seen screaming headlines on Facebook, Twitter, or elsewhere about impending extreme weather. In the last few weeks I have seen wild stories about a late-season tropical storm forming in the Caribbean and an Arctic outbreak and snowstorm heading through the eastern US all the way to the Gulf. Neither of these had any real chance of occurrence but the people who post them are looking for clicks and attention. Garden Professors’ blog readers already know about misleading information in social media (Epsom salts and cardboard mulch, for example) but may not know much about weather forecasting and how it is misused in these click-bait posts to gain attention for weather that probably will never happen. This blog post will describe how weather forecasts are made so that you can understand which forecasts are the most reliable and useful for gardeners and others who work and play outdoors.

Types of weather forecasts

In general, forecasts can be categorized in several ways. They can be categorized by time period (nowcasting, short-range, medium-range, long-range) or by method (based on evolving weather conditions, statistics of past weather, or numerical weather prediction by computers). Forecasts related to time just indicate how close to the actual weather occurrence you are making the prediction. A “nowcast” is a forecast for the immediate future up to about six hours ahead. Short-range forecasts usually cover 1-3 days, medium-range 3-7 days, and long-range forecasts are made more than a week ahead. Long-range forecasts tend to provide more general descriptions of climate patterns and departures from climate conditions rather than specific weather conditions because accuracy decreases as you go farther ahead in time. This is one clue that a specific social media forecast map is likely to be unreliable because we cannot make specific predictions of atmospheric conditions more than about a week ahead due to lack of sufficient data, simplifications in the computer models used to make predictions, and chaos in atmospheric conditions that cannot be easily described by the input data to forecast model programs.

Methods for making weather forecasts can also vary. The simplest one says that today’s weather will be the same as what happened yesterday. It works well in regions and seasons when the weather does not change much from one day to the next but is poor where more dynamic weather occurs. One step up is what we call an advective forecast, which predicts changes in temperature, moisture, and other properties due to the horizontal movement of air by wind. Forecasters determine this by looking at wind direction and the temperature and other conditions of the air that will be arriving from upstream. If air is blowing in from the Gulf, for example, the weather is likely to turn warmer and more humid, while air arriving from the Arctic is likely to be colder and drier than what is already present. Similarly, you can sometimes use observations of clouds to make simple weather forecasts based on how they change over time. Climatological forecasts look at past weather occurrences on the dates for which you are forecasting and describe the statistical likelihood of specific temperatures and rainfall conditions. Some also look at analogs from previous weather situations that look like the current conditions and predict that the future weather conditions will occur again based on past performance.

Using computers to predict weather

Most forecasts used by modern meteorologists use numerical weather prediction to forecast future weather patterns by entering observational atmospheric data into complicated computer models that use the physical equations of motion to determine how the atmosphere will change in response to moving air, development of clouds and precipitation, and interactions with land and ocean surfaces at the ground and put the results into map formats that provide a graphical depiction of what the weather will be like in the future that can be interpreted by meteorologists to provide the expected local conditions (these are called deterministic forecasts). There are multiple weather models that are run by different groups, including US-based models as well as those from Europe, Canada, Japan, and other countries with large computing facilities.

Most models are run for a variety of different starting conditions to give a range of possible outcomes, and the combination of different model runs and different models lead to what is commonly called “spaghetti models” that show each individual model solution on the same map. The closer together all the runs are in the future, the more confidence we have that the models are in agreement, but if they are spread out, forecasters have low confidence in what will occur. Expected impacts at any one location change depending on which computer run is used. Many of the extreme weather events shown in maps show by social “media-rologists” are from a single computer run far in the future showing the worst possible case, even though there may be 99 other computer solutions that show something much less severe. The social media folk are showing whatever extreme case will get them the most attention (and clicks), which allows them to monetize their accounts by promoting the worst-case event, no matter how unlikely, not the most likely one. Long-range forecasts which look at all the solutions may use statistics to determine where the storm is most likely to go and base the probability on the range of individual model runs we see (these are called probabilistic forecasts).

How accurate are weather forecasts?

Despite the common belief that weather forecasts are seldom right, the statistics show that they are very accurate. People generally only remember the few occasions when they are wrong, not the many when they are correct. Today’s forecasts are better than in the past because computers are getting larger and more complex and more data are being collected to feed into the models, including satellite data that fill in holes in surface data over the oceans. A daily forecast now is likely to be good at least 7 days in the future, compared to 5 days twenty years ago. In the future, we may see even better results using artificial intelligence (AI) to fine-tune forecasts, as we did this year with hurricane track forecasts. But we will never be able to provide an accurate daily weather map 90 days in the future, so don’t count on the long-range forecasts to tell you what to expect on the day of your summer garden party when you are planning in January or even in April). If you need that forecast to plan for the likely weather, using climatological information is your best bet.

The best weather forecasts for gardeners

Your best source of accurate weather forecasts in the United States is the National Weather Service. Most other countries provide forecasts from their own government weather services. If you need to plan for specific times for gardening projects such as spraying products that require dry conditions or mowing, hourly forecasts for up to 6 days ahead can be found using the information at https://site.extension.uga.edu/climate/2018/03/where-to-get-hourly-weather-forecast-information/. Keep in mind that the farther ahead in time you get, the less accurate they will be. Weather information from private forecasters, including broadcast meteorologists and commercial companies that provide handy apps for cell phones, mainly base their forecasts on NWS predictions but often add value by providing descriptions of conditions, specific impacts on sectors like agriculture and transportation, or pretty graphics to make the forecasts look more appealing. Gardeners should keep in mind that most weather apps on phones are fine for daily planning but are not suitable for rapidly changing weather conditions like severe weather, since they are not updated often enough to factor in these short-term events.

Gardeners who want to maximize their outdoor activities need access to accurate and believable forecasts so they can plan the use of their time effectively. By understanding the nature of weather forecasts and the dangers of exaggerated predictions of likely future weather conditions, they can make the best use of their time and enjoy their garden work without worrying about overhyped extreme events that likely won’t happen.

This time of year, I frequently notice the change of the sun’s daily position over time, since my family room faces east. This is especially true as most of my trees on that side of the house are deciduous—as the leaves fall, I get a better look at where sunrise is actually occurring and how it is changing day by day. Sun angle and the amount of sunlight that reaches different parts of your garden can have a big impact on what kinds of plants you can grow and how your garden appears. This impact changes daily as well as seasonally and is based on your garden’s orientation. In this post we will discuss how the sun angle affects gardening and how you can use sun angle to help plan your garden.

How sun angle and day length change with the season

The tilt of the earth’s axis of rotation causes the path of the sun across the sky to change throughout the year. When the North Pole is pointed towards the sun (Northern Hemisphere summer), the sun is high in the sky, days are long, and the light is the most intense. This can lead to high temperatures and the risk of sun scorch or heat stress on sensitive plants where direct sunlight is strongest. When the North Pole is pointed away from the sun (NH winter), days are short, the sun is low in the sky, and the light is generally weaker. Shadows are longer and stretch further, which means that an area that might get full sun in summer may be entirely shaded in winter. This can limit gardening options in colder months even in areas where there is no frost.

In spring and fall, the sun’s angle is intermediate and changes more quickly from one day to the next. Of course, if your garden has deciduous trees, shade will also be affected by the leaf-out of those trees and will increase as the leaves grow and expand, so the type of surrounding tree cover will also be a factor.

You can find a useful tool to help you determine the direction of the sun at any time and place at https://sun-direction.com/.

Cloud cover and sunlight

In the real world, the sun doesn’t always provide much light if you are in an area with a lot of cloud cover. Some areas have a lot more cloud coverage than others due to the effects of mountains or water bodies that help form clouds. Cloud cover can also vary depending on the season and what types of weather are affecting a particular region. Where I grew up in western Michigan, the effect of lake effect cloud cover made winters and springs quite gloomy and any sunlight was welcome. However, in summer the prevailing wind shifted from the northwestern flow that occurred in winter to winds that were primarily from the south. As a result, our summer weather was much sunnier and warmer because of the increased sun due to fewer clouds. You can see a video of the seasonal cycle of cloud cover across North America here or see monthly maps over the United States in Brian Brettschneider’s Climate Blog. If you are in an area with a lot of cloud cover, especially during the growing season, you will need to factor that into your planning, since clouds reduce the amount of incoming sunlight and influence photosynthesis.

How sun angle and light exposure affect plant growth

The amount of light that hits a plant will directly control photosynthesis and plant development. Since plants use light energy for photosynthesis, the more light-hungry a plant is (like fruiting vegetables), the more hours of direct, intense sunlight it needs (typically 6-8 hours or “full sun”). Shade and insufficient light will result in weak, leggy plants with poor fruit or flower production. If the sunlight is unevenly distributed, the plant will grow and bend towards the light source, resulting in weaker stems or an uneven shape.

The amount of sunlight that an area gets will also affect the types of plants that grow in a given location. Areas with high-angle, intense sun develop thicker, shorter leaves to minimize water loss. These areas are also often areas of higher temperatures and drier conditions, which contribute to the types of plants that grow there naturally. Plants that grow in low-angle, dappled, or indirect light often have thinner, larger leaves to capture as much of the light as possible.

Using sun angle to help with garden design

Understanding the sun angle and light distribution in your garden is essential to good garden design. By observing the movement of the light and shaded patches in your garden over the course of the day and across the seasons, you will be better able to choose the best plants for the exposure you find in each part of the garden. You might even want to create a diagram of your garden to identify different areas of light exposure. You should match the plants’ light requirements (full sun, partial shade, full shade) to the appropriate areas you have.

In addition to determining where shaded and sunny areas are, you also need to consider the effects of trees, especially if they are deciduous and change over the course of the year. If you want to provide an area with more sunlight in your garden to produce crops like tomatoes, you may wish to consider some pruning of tree branches to provide more sunlight to those areas. You should also think about the impacts of taller garden plants on surrounding vegetation, so you should plant taller plants on the north side (in the Northern Hemisphere) so they do not shade shorter plants.

Protecting plants from too much sunlight

If your sunlight is too intense for some sun-sensitive crops like lettuce, you may be able to erect temporary shade structures to help protect them from the strongest sun. Farmers also use kaolin clay and similar products to help prevent sunburn in commercial plants by covering them with a white layer that reflects sunlight away and keeps the fruit cooler and less affected by strong sunlight. It can also help repel pests by creating a protective barrier on plant surfaces. You can tell if plants are getting too much light by observing leaf scorching (brown, crispy spots, especially on the edges), bleaching (leaves turning pale yellow or white), wilting, and stunted growth.

How sun affects gardeners

We all love the sun and our gardens need it to grow, but too much of a good thing can be hazardous to the health of gardeners as well as plants. Make sure that you wear sunscreen and use hats and clothing to help protect yourself from the harmful aspects of sunlight and you will be free to enjoy your garden without fear of skin cancer and health issues. Let the sun shine and let our gardens (and gardeners) grow strong!

As a lover of the weird and wonderful, October is one of my favorite months of the year, because of Spooky Season. To celebrate, I thought it would be fun to learn about some of the weird and wonderful plants around us, especially some of the most notorious: carnivorous plants.

Whether you like to grow them, observe them in their natural habitats, or simply just learn about them, it’s easy to understand our collective fascination with carnivorous plants. Many of us may have seen depictions of ‘man-eating plants’ in horror movies, or exaggerated tales of some of these killer plants in fictional stories, cartoons, and other pop culture references. The horror genre’s elaborate and embellished portrayals of carnivorous plants were inspired by Charles Darwin, before which plants were considered to be innocent bystanders to the ecological phenomena surrounding them. Having spent 16 years researching carnivorous plants, Darwin published multiple books about them. This shifted our perception of plants as a whole and how they interacted with other organisms, giving rise to our fascination with carnivorous plants, driving our desire to understand their biology, and fueling our creativity by exaggerating some of these adaptations into very entertaining science fiction. I wonder If he could have ever imagined the creative ways in which popular culture (especially science fiction and horror) would go on to embrace these botanical marvels.

Types of Carnivorous Plants

Carnivorous plants are defined as plants that extract nutrients from animals. These plants have a variety of adaptations that allow them to capture and/or trap prey (most often insects and other arthropods), and enzymes that can break this prey down into nutrients that can be used by the plants themselves. Although carnivorous plants do still perform photosynthesis, they get most of their nutrients from captured prey.

Some of the more famous carnivorous plants include the charismatic Venus fly trap (Dionaea muscipula), the North American native pitcher plants (Sarracenia spp.), the tropical vining pitcher plants (Nepenthes spp.), the widespread sundews (Drosera spp.) and butterworts (Pinguicula spp.), and the moisture-loving and often aquatic bladderworts (Utricularia spp.). Some not as well-known examples include a few species of carnivorous Bromeliads (in the genera Brocchinia and Catopsis), and Triphyophyllum peltatum that can become carnivorous in situations of nutrient scarcity, after which it may revert to a non-carnivorous lifestyle. There is also a plant called the Gorgon’s Dewstick (Roridula gorgonia) which captures insects, but lacks the mechanism to digest this captured prey. Instead, this fascinating plant will trap this prey to attract the jumping tree bug (Pamerida spp.) which feeds on these trapped insects, while leaving nutrient-rich frass (insect poop) which is absorbed by the leaves of this plant!

The ways that plants actually capture their prey are pretty diverse: ranging from sticky substances that can immobilize prey, dark tubes and funnels that can trap and disorient them, and mechanical methods that can snap/ensnare or suction prey, dooming them to their fate. These mechanisms are defined as ‘active’ or ‘passive’ based on whether there is movement involved in the prey-capture process.

Evolution of Carnivory in Plants

Although we previously lacked a deeper understanding, advancements in molecular biology have allowed us to paint a more complete picture regarding how plants actually evolved this interesting adaptation.

Carnivory in plants is another classic example of convergent evolution (where unrelated species independently evolve similar traits), with instances of its occurrence over 12 different occasions across the evolutionary timescale of flowering plants (angiosperms). We currently estimate that carnivory is evident in over 800 species of plants across more than a dozen plant families.

All of these instances of carnivory were driven by similar needs: limited nutrient availability in the habitats in which these plants grow. These carnivorous plants grow in conditions which lack specific nutrients essential for plant growth (many of which include bodies of water or soils that are low in Nitrogen and Phosphorous). Arthropods such as insects can be excellent sources of these (and other) essential nutrients, and are often abundant in these habitats…all that plants needed to do was to come up with a way to tap into this great resource. They were able to accomplish this by repurposing existing genes to capture these six- and eight-legged snacks, and extract the nutrients found within them. Researchers who evaluated the digestive enzymes found in these plants noticed that there were quite a few similarities between these and defensive chemicals used by ancient flowering plants to protect themselves from pathogens and pests. Most carnivorous plants use similar enzymes including chitinases, proteases, and acid phosphatases (all of which have roles to play in the breakdown, dissolution, and absorption of nutrients from the corpses of their arthropod prey). In an interesting evolutionary twist, these chemicals were repurposed to eat some of the pests that they were originally protecting the plants from! How cool is that?!

If you want to learn more about the evolution of plant carnivory, I recommend reading the wonderful Smithsonian article linked in the resources below.

Carnivorous Plants and their Pollinators

With plants that have evolved to kill and consume arthropods, one can’t help but think about the pollinators that they depend on. How can plants attract both prey and pollinators? How do they go about selectively capturing the ones that they kill and extract nutrients from, while also protecting the ones that they rely on for pollination?

Insect and plant relationships can be multi-faceted, interesting, and extremely sophisticated (and plant/pollinator interactions are arguably some of the most interesting of these). Carnivorous plants have come up with ways to navigate this ‘pollinator-prey conflict’ utilizing a few main mechanisms. These include separation of the traps from the flowers, which is either done temporally or spatially. Some carnivorous plants will bloom before the traps have developed, allowing them to be successfully pollinated before they begin capturing prey, while other plants may physically separate the flowers from the traps themselves, often positioning flowers much higher than the traps which would be found closer to the ground (the method used by the Venus Fly Trap). They may also use different attractants (such as odors and colors) in their flowers and their traps to attract specific pollinators to flowers and only prey to traps; or they may use a combination of the aforementioned strategies.

Growing Carnivorous Plants

Although many carnivorous plants can have complex growing requirements that can make them difficult to grow in captivity, there are quite a few plants that are well-suited to this. Furthermore, we all know some very ingenious gardeners that can grow some of the trickiest plants with ease, laughing in the face of what others may consider ‘impossible’! My mother is a classic example of one of these gardening goddesses who manages to propagate and grow some of the most ‘difficult’ plants, often the ones that I have told her will probably not be successful. To those of you who are like my mother, I salute you. For the rest of us, I will focus on some carnivorous plants that are more user-friendly.

There are a variety of carnivorous plants that grow well indoors, and several available resources to help troubleshoot growing requirements (including a variety of websites and blogs that are dedicated to carnivorous plants, some of which I have included in the resources below). For beginner-friendly carnivorous plants, I would recommend starting with Venus fly traps and sundews. Often far less fussy than most, these are sometimes considered ‘gateway’ plants for those who might be starting out on their carnivorous plant journey. Tropical pitcher plants (Nepenthes spp.) are another popular houseplant choice, and these vining beauties can be attractive additions to your carnivorous collection.

There are also a few carnivorous plants that can grow well in outdoor gardens as long as the appropriate conditions are present. The purple pitcher plant (Sarracenia purpurea) is an example of a cold-hardy carnivorous plant that is especially suited to growing outdoors in North America (in USDA Plant Hardiness Zones 3-8), but there are also other temperate species of carnivorous plants that grow well in outdoor gardens in other temperate regions, and tropical carnivorous plants that are better suited to growing in more tropical regions. The most common carnivorous plants grown in outdoor gardens include temperate pitcher plants (Sarracenia spp.), sundews, and the Venus fly trap. I encourage you to look into the carnivorous plants of your region to see what could possibly grow in your home gardens. Note: you should never remove native plants from their native landscapes, because this could damage some of the fragile ecosystems in which they reside. Instead, source suitable plants from reputable suppliers who grow and propagate them sustainably.

Like any plant growing recommendations, there is never a one-size-fits-all approach to caring for carnivorous plants, nor are there plants that work well in every single situation. One of the keys to growing carnivorous plants is to make sure that you are providing these plants the right kind of growing conditions for them to thrive, often mimicking the conditions in which they thrive in nature. Most of these carnivorous plants need bright light, and supplemental lighting may be necessary if you don’t have a suitable location with access to enough sunlight. They also need lots of mineral-free water (many use distilled water for this), and nutrient-poor soils. You can even purchase carnivorous plant-specific soil mixes to simplify this process. Humidity is another consideration, and humidifiers, misting, or using terraria that can maintain humid conditions may be necessary. These plants don’t need to be fertilized, and it is important not to overfeed them. Indoor plants can be fed one or two insects per month (don’t feed them meat), whereas outdoor plants will probably not need to be intentionally fed, (as they can often get their insect nutrient sources on their own), but make sure they are grown in a location that has access to insect prey.

(If you are a carnivorous plant caretaker, what are some of your favorites to grow?)

More Information:

Carnivorous Plants (Penn State University):
https://extension.psu.edu/carnivorous-plants

How Carnivorous Plants Evolved:
https://www.smithsonianmag.com/science-nature/how-carnivorous-plants-evolved-180979697/

El-Sayed, A., Byers, J. & Suckling, D. Pollinator-prey conflicts in carnivorous plants: When flower and trap properties mean life or death. Sci Rep 6, 21065 (2016). https://doi.org/10.1038/srep21065

Some Resources for Growing Carnivorous Plants:

https://carnivorousplantnursery.com/blogs/cpn-blog

https://www.carnivorousplants.org

https://tomscarnivores.com/blog/start-here

I wanted to share a new study that came out this week in the journal Science. We generally agree how important bees, butterflies, and other pollinators are, not only for our crops but for the health of ecosystems as a whole. Yet, despite decades of awareness, pollinator numbers continue to decline worldwide. Dr. Gabriella Bishop used a meta-data approach in this study to examine why pollinators are struggling. The study concluded that current conservation targets for habitat area are simply not large enough.

The project combined datasets from 59 studies across 19 countries to measure how populations of wild bees, bumble bees, hoverflies, and butterflies respond to natural habitat around farms. I was fortunate to contribute some of my previously collected data on pollinator communities in the California Central Valley and be included as an author. Overall, by combining datasets, Dr. Bishop had information on 178,000 insects collected from 1,200 field sites, which allowed for the calculation of the minimum amount of habitat each group needs.

Many global and regional policies, like the EU Biodiversity Strategy, suggest setting aside about 10 percent of farmland as habitat for pollinators. But Dr. Bishop found that pollinators need far more space to thrive. The minimums vary group, with solitary bees needing ~16% in temperate areas and ~38% in the tropics. Butterflies needed ~37%. Hoverflies were more flexible, with the lowest threshold for habitat requirements at ~6%). Overall, this means hedgerows, woodlots, meadows, and wildflower-rich grasslands must make up a much larger share of the landscape if we want to halt pollinator declines. And critically, these areas need to be managed for the long haul. Short-term fixes such as seasonal wildflower strips can provide temporary boosts, but they do not sustain pollinator populations in the long run.

For gardeners and land stewards, the message is clear. Every patch of habitat counts, but scale does in fact matter. Planting flowers that bloom across the seasons is important, but so is maintaining semi-natural spaces for decades, not just years. If we want future generations to enjoy these insects, we must think BIGGER.

In my household, the weather is a common subject of conversation. That is only partly because I am married to a meteorologist. In fact, I have noticed that I can talk to almost anyone about the weather, and I suspect you can too. Weather is most captivating when something interesting is occurring, like liquid falling from the sky. When I give talks to master gardener groups, they are almost always consumed with how the weather is affecting their gardens. I get more questions about drought from these groups than almost any other topic, but rainfall, past or future, is also a frequent subject.

Today we will look at different types of precipitation, how they are formed, and how they affect garden plants. This is especially important as we move from summer, when rain is the most plentiful hydrometeor, into fall, when freezing rain, sleet, and snow become more frequent. Of course, this depends on where you are, and some Northern Hemisphere southern areas will experience almost no snow while for northern regions, it is the majority of what is observed.

What types of precipitation are there?

When I started writing my post, I looked online to see how many different types of precipitation were listed. I found that there is quite a variety in the number of types listed, ranging from two to seven varieties. I am going to lump them into two basic categories: liquid and frozen. But there are subcategories within these two basic buckets, especially in frozen precipitation, which includes snow, sleet, ice pellets or graupel, freezing rain, and hail. We will see how they are related to each other and yet distinct.

What is rain?

Rain is essentially liquid water that is falling from the sky and hitting the surface. If the air is dry enough, rain that develops in clouds evaporates before it gets to the ground, and that is called virga. Raindrops can form in tropical clouds through a liquid process that involves the collision and coalescence of small water droplets into larger drops that get heavy enough that they cannot remain suspended in the air and fall to the ground. But you might be surprised to know that most liquid rain starts as snow high up in the clouds, where the temperature higher up in the atmosphere is below freezing. We’ve addressed some characteristics of rain and how they affect gardens in previous posts here and here.

Clouds (except those in the deep tropics) are made up of a mix of supercooled water droplets and ice crystals that float around together, but it is easier for the ice crystals to grow by sucking up water vapor than for the water droplets to grow, so the ice crystals usually dominate the process of producing precipitation and snowflakes are the result. As these snowflakes fall towards the ground, they fall into warmer air near the surface and melt into the liquid water drops that make us wet. A light rain with small water droplets may be just a drizzle, but a thunderstorm with a cloud that is 10 miles deep could have water droplets as large as 0.34 inches, although I have heard unconfirmed stories about raindrops more than half an inch across in the heaviest rain events.

What types of frozen precipitation are there?

When precipitation freezes, it can take different forms depending on the temperature of the air that it falls through. If the air that the original snowflake falls through is below freezing through the entire depth of the atmosphere, then it remains as snow all the way to the ground. The shape of the snowflake depends on the combination of temperature and humidity that is present where the snowflake forms. They can take on an amazing variety of shapes beyond the typical dendrite that we usually associate with snow. The dendrites we often see falling in winter are ideal for blanketing the ground with a carpet of white, and their shapes make them able to trap a lot of air in the snow cover, providing insulation for the soil that keeps the temperature there relatively warm by protecting it from the cold and dry air the snow is falling through. In other words, it acts as a mulch to protect the ground and the plants there.

If the snowflakes from aloft fall through air that is above freezing, they transform from snowflakes to other kinds of precipitation, as shown in the diagram below. If the warm layer is deep, all of the snow changes back to liquid raindrops. If the air is above freezing but the surface is below freezing, then freezing rain occurs. The water sticks to trees, wires, and buildings, adding to their weight and collapsing them if the accumulations are thick enough. If the warm layer is relatively deep, but the air above the surface is below freezing, the water droplets may refreeze, leading to sleet or clear ice pellets. If the layer is thinner, the snowflakes may develop a coating of liquid water that surrounds the snow crystals from supercooled water in the clouds, encasing them in ice, leading to snow pellets or graupel, which are opaque instead of clear like sleet.

Hail is another variety of frozen precipitation that forms in summer thunderstorms, which can be as much as 10 miles high. In those storms, snowflakes can circulate vertically inside the storms due to strong updrafts, gathering a new coating of ice each time they move upward through the clouds, growing larger each time they cycle up and down. The largest hailstone ever measured was 8.0 inches in diameter and weighed 1.9375 pounds. It was discovered in Vivian, South Dakota on July 23, 2010. You will often find layers of clear and cloudy ice in hailstones as they travel up and down through the thunderstorms. Hail that is much smaller, as little as 0.25 inches, can cause damage to plants and crops as the hailstones shred leaves and cause damage to fruits and vegetables, leaving them unsightly and vulnerable to mold and pests.

How do different types of precipitation affect garden plants?

The most damaging types of precipitation for gardens are those that add weight to plants or cause impact damage when they hit something. Heavy snow and freezing rain can cause tree limbs to break due to increased weight, which trees cannot withstand, especially when they are still leaf-covered in fall or when they are not well maintained and have weak points in their structure. Garden plants can also be flattened or otherwise damaged by the heavy ice or snow cover. Previous advice in the Garden Professors by Linda indicates if the snow is really heavy, it should be removed from the plants before it can do damage, although lighter amounts can remain. On the other hand, snow cover on the ground can be a benefit to your garden if it incorporates enough air to serve as an insulating layer between the plants near the ground and the colder and drier air above it.

Hail, especially heavier stones, can cause significant damage to leaves and can defoliate gardens or farm fields completely in just a few minutes if the hail is intense enough. Even small hail can destroy tender plants, fruit, and flowers or at least damage the skin or leaves enough to decrease their value as crops due to cosmetic blemishes and places where diseases or insects can enter the plants. Gardens should be assessed for hail damage soon after a storm occurs, since the damage can be harder to spot over time.

How else can precipitation help gardeners with their gardens?

A previous post on GP noted that observing your garden after a heavy rain can be helpful in determining what the drainage patterns are and what might need to be addressed. While you might not be able to do much work in your garden right after a heavy rain event, it provides an excellent time to make future plans to make your garden more weather-proof.

Rain and snow, along with the other varieties of precipitation we experience, provide valuable moisture to our gardens as well as protection to plants in winter, but can also produce damage that can harm our garden plants. Enjoy the rain (or snow) when it comes, but be aware of the negative impacts it can have on your garden, too.

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.