John Porter

Plant Disease Primer: Part 1 – Shaping up the causes, signs, and symptoms of disease

Throughout the garden season, extension professionals all across the country get to play detective when trying to diagnose plant diseases and recommend specific controls or preventative measures. We often have to put on our Sherlock Holmes-esque thinking caps and our standard issue detective’s magnifying glass (or microscope) to diagnose plant maladies.

Having a basic understanding of diseases, how they function, and what they look like is key. Gardeners who bring samples or pictures into our office often get exasperated when we play twenty questions trying to figure out if it is a fungus, bacteria, or virus (or something else) causing the issue. Knowing about placement, environment, planting, etc. can all be keys in discovering what might be causing the issue. Sometimes we can’t identify an exact disease at a glance and have to send things to the diagnostic lab on campus, but by looking at signs and symptoms and identifying factors about the plant we can often figure out the type of pathogen causing the issue, or whether it might be environmental, abiotic, or insect related.

What leads to plant diseases?

Of course, the thing that causes the disease is a pathogen or a causal agent such as a fungus, bacteria, or virus (or a few other odds and ends like phytoplasmas). But there are other factors at play to get a disease infection started and sustained. You need all of the factors in place for infection. This is often represented as a triangle, where a causal agent (pathogen) must be present with the right environmental conditions and a host plant that can actually be infected by the pathogen. I’ve also seen a plant disease “pyramid” where time is added as another factor (as in, the correct conditions must be present at the same time and for a long enough period for infection to start). And still yet in researching this article I found the PLANT DISEASE TETRAHEDRON, which adds human activity as another factor. What’s next, the plant disease fractal?

But I digress. When a sample comes in to our office, we play twenty questions with the gardener asking about these different factors. Like is it irrigated (many diseases need water to be spread or to develop), does it get shade or full sun, have you seen any insect activity, when do you usually work in the garden, etc. These questions can help us identify parts of the disease triangle/pyramid/tetrahedron that could inform the diagnosis.

Keeping these factors in mind can also help gardeners reduce the likelihood of disease through IPM. For example, viruses require a vector – usually an insect, animal, or human to spread the disease. Many viruses are spread through leafhoppers, bacterial wilt in cucurbits is spread through cucumber beetles, and mosaic viruses like tobacco mosaic virus has many vectors including humans and garden tools (which is why many green industry businesses have strict sanitation rules, including rules for tobacco users and hand sanitation). Knowing that fungi and bacteria can be airborne with spores or splashed by “wind splashed rain” or irrigation water can lead to improved practices like mulching, pruning for good air flow, and plant spacing.

How can you tell which diseases are which?

Let’s face it, many plant diseases look very similar. There are usually what we call spots and rots that can be very similar. But there are some identifying characteristics that help us at least determine what type of pathogen or causal agent is causing the issue.

The first thing to keep in mind is that plant diseases have both signs and symptoms. Signs are the presence of the actual disease causing organism, visible to the eye. Fungal diseases often have mycelia, or fungal threads, and reproductive structures like pycnidia present. You may also see the causal agent itself, such as leaf rust or powdery mildew. Bacteria will often have exudates that ooze out of plant parts, water soaked lesions, and bacteria that stream out of cut stems parts. You can actually diagnose some bacterial infections by suspending a cut stem in water and watching bacteria stream/ooze out of the cut. Viruses are not visible to the human eye, therefore do not have signs.

Powdery mildew on peony Source: Douglas/Sarpy Extension – Nebraska

Symptoms, on the other hand, are the effects of the pathogen on the plant. Common symptoms of fungal infections are leaf spots, spots or rots of fruits, chlorosis, and damping off in new seedlings. Bacterial symptoms include leaf spots (often with a yellow halo around them), crown gall, stem/trunk cankers, wilting, shepherd’s crook (like fire blight), and fruit rots. And since bacteria usually depend on streaming through liquids, they often leave definitive patterns for leaf spots that align with vein structures. For example, leaf spots will often be angular because they are “trapped” in between veins on the leaf. The most common symptom of viruses is a mosaic pattern on leaves and fruit, but also crinkling and yellowing of leaves, necrosis, and stunting.

Angular leaf spot on cucumber – the symptom pattern falls within veins, giving the angular appearance. Source: UMN Extension

Special mention- phytoplasma: Phytoplasmas are single-celled organisms that aren’t really bacteria, but are descended from them. They don’t have cell walls and are transmitted to plants through an insect vector like leaf hoppers. The most common type of phytoplasma diseases is called yellows (aster yellows, ash yellows, etc.) because plants often turn yellow. The symptoms are often interesting. Witches brooming, which is irregular growth that makes branches look like brooms is common. Aster yellows is a common disease affecting many plants in the aster family. Most commonly, flowers of these plants look distorted and may grow leafy structures instead of flower structures.

Unusual floral growth as a result of aster yellows Source: Douglas/Sarpy Extension – Nebraska

To wrap it up

It can be difficult to figure out what diseases are affecting plants, if it is a disease at all. Getting help in determining what disease might be affecting plants can help you treat or prevent the problem in the future. In my next installment of this series, I’ll talk about common diseases, their signs and symptoms, and treatments and preventative measures.

Sources:

https://www.canr.msu.edu/news/signs_and_symptoms_of_plant_disease_is_it_fungal_viral_or_bacterial

https://lms.su.edu.pk/lesson/1660/elements-of-an-epidemic

¡Escandalo! Seedy mixup results in #Jalapeñogate drama across the US

There’s a scandal simmering all across the United States that brings to mind a switched at birth storyline on a steamy soap opera or telenovela. This scandal, though, isn’t about babies, its about….peppers! Jalapeño peppers, to be exact.

The issue, dubbed #Jalapeñogate online, has many home gardeners scratching their heads as to the identity or the issue with the peppers that they planted. You see, instead of those glossy dark green peppers that many are used to putting in their salsas and other favorite spicy dishes, the plants are producing bright yellow peppers. Some of them are the same shape as jalapeños and some look more like banana peppers.

A local gardener allowed me to stop by and let me check out their mysterious peppers.

The phenomenon has gardeners, farmers, and officials in multiple states scratching their heads. It turns out there are no stolen tapes with evidence of the problem. Instead, I was first alerted to the problem when some of the garden Facebook groups in Nebraska were abuzz with posts about the mystery peppers. I’ve since seen news I’ve seen the issue mentioned in news articles from Oklahoma, Kansas, and California and have seen posts on social media sites such as Reddit and TikTok. I scoured many of these sources (TikTok was surprisingly the most informative) and confirmed it with info from friends in the seed industry.

So what happened? It turns out that the seed trade is global and multi-tiered and sometimes mix ups occur. It just so happened that this year there were a lot of them. One US seed company that supplies a lot of seeds to nurseries and other seed companies, called Seeds by Design, imported some of its seeds for the current season. The company supplies many interesting and niche seeds, many of which it develops or breeds (they are responsible for the award winning Chef’s Choice tomato series and several other vegetable cultivars that you’d recognize on the seed rack). But it also purchases or imports seeds often for more common varieties. Seeds by Design supplies seeds to many nurseries, growers, and even seed companies around the country. And that’s where the trouble starts.

I mentioned #Jalapeñogate on our TV show Backyard Farmer, which fanned the fiery (and not so fiery) pepper flames in Nebraska.

The company imported seeds from an international grower that turned out to be mislabeled. Up to five different cultivars were accidentally swapped and resulted in pepper pandemonium across the country. It turns out that more than jalapeños were affected, so we should really change it to just #Peppergate. Here’s what was switched:

What was supposed to be…	Turned out to be…
Jalapeño (green cultivar)	Jalapeño ‘Caloro’ (yellow cultivar)
Jalapeño ‘Tam’ (mild green)	Sweet banana pepper
Hungarian Sweet Wax	Bell Pepper ‘Diamond’
Bell Pepper ‘Chocolate Beauty’	Sweet Pepper ‘Red Cherry’
Bell Pepper ‘Purple Beauty’	Hungarian Hot Wax

Gardeners could have bought these at local garden centers or nurseries as transplants. I know of at least two local/regional garden centers that sold the affected plants. I’ve also seen that gardeners who bought seeds from some suppliers (I’ve only seen Ferry-Morse so far) may have received at least switched bell peppers.

Nebraska gardeners (at least 90 of them) were quick to share their #Peppergate story with me.

What does this say about our seed and food supply?

Our food system and our seed system are global. We live in a global economy and companies buy and trade with each other all the time. Given the scale of this trade, mistakes can and do happen. I’ve seen some people try to drag Seeds by Design because they purchased seeds from a foreign company that just happens to be in China. But the company doesn’t deserve that. They had no knowledge of the mix up until the peppers were in the hands of growers and peppers didn’t look right. Can you tell the difference between pepper cultivars by seed?

And others have tried to make an issue about trading with China with some comments that hint at outright racism. While there are some security concerns about trading with countries like China, especially in the tech world, trading simple commodities like Jalapeño seeds is standard practice. I’ve also seen comments that importing ag products from other countries means that we can’t support ourselves. But it turns out that we sell a whole lot more agricultural goods to China than we buy. US producers sold a record-breaking $200 billion (with a b) worth of agricultural products to China in 2022 while we imported $9.5 billion from them.

Given the need to feed so many people economically, we often import from countries that have better capacity to grow what we need due to climate, land, and labor differences. We also have to take into account seasonal differences. Even US based seed production companies and breeders will grow in other countries to take advantage of multiple growing seasons. Given our reliance on horticultural imports, we have a robust inspection system to make sure the foods, plants, and seeds we receive from countries like China are indeed safe.

To wrap this mystery up –

While there’s not much you can do now that you have these mystery seeds, enjoy the fun of trying something unexpected. If you ended up with a pepper that you don’t like or can’t eat (like the Hot Wax for Purple Bell switch), share with friends or donate to a local food pantry. After all, you can’t tell that the jalapeño isn’t green when it’s turned into a jalapeño popper.

Sources

https://www.fas.usda.gov/data/record-us-fy-2022-agricultural-exports-china

Don’t get hosed: exploring the efficiencies of garden and landscape irrigation systems

As many parts of the US face drought or dryer than normal conditions and issues about water availability especially in the western states, many gardeners are reassessing their relationships with plants and irrigation. Many gardeners, especially in the west, are replacing their lawns and landscape plants with more drought and dry-weather tolerant options. But there still are times when irrigation might still be necessary, e.g., growing vegetables and fruits, establishing new plants, and more. Using water efficiently and effectively is key in these situations even when water is available and drought conditions aren’t as prevalent. Efficient water use and good irrigation can also mean a savings on the water bill AND a reduction in plant diseases spread by water application on the leaves. Paired with mulching, efficient irrigation can drastically reduce the amount of water used in gardens and landscapes.

In order to make the best choices for your garden, I’m going to talk through some of the most and least efficient irrigation methods for your gardens and landscapes. I’ll be starting with the most efficient methods and working my way to the least.

Drip Irrigation

Drip irrigation is considered one of the most efficient methods of irrigation because it applies water directly to the soil at the base of the plant and therefore typically uses the smallest volume of water. Research shows that drip irrigations have around a 90% efficiency rate. . Most systems sit above the ground and apply water to the soil surface, but some sub-soil systems are available. The system usually involves a filter and pressure regulator to keep the emitters functioning and applying water at the proper volume.

This drip tubing has pre-installed emitters along the tube and drips small volumes of water directly on the soil near the plant.

The efficiency of drip irrigation comes with a caveat though. When applied to sandy or rocky soils, water from drip irrigation has a much smaller spread laterally in the soil due to less capillary action and higher gravitational pull due to the large pore spaces. This means that there isn’t as much coverage of water in the root zone. In order to combat this drip emitters must be closer together or have a high flow rate, both of which increase water usage and reduce the effectiveness of drip irrigation in sandy soils. Read more here

Source: Soil Type Influences Irrigation Strategy, MSU Extension, Ron Goldy

There are typically two types of application methods: tubes or tape that have pre-made emitter holes at set distances that disperse a set amount of water per hour or emitters that are inserted into the end of solid tubes (that may or may not have an adjustable flow rate). The tubes and tapes that have holes pre-made are typically used in vegetable gardens, row crops, or in beds where plants are uniformly planted. Systems with the inserted emitters are often used in landscape settings where it makes sense to water individual plants, such as trees, shrubs, or large perennials.

Given the low volume of water disbursed by the system, water pressure is regulated in a way that ensures even distribution as long as it isn’t modified than from the manufacturer or factory specs.

For information on installation and maintenance, check out these resources:

Drip Irrigation for Home Gardens – Colorado State Univ. Extension

Irrigation Video Series – Oklahoma State Extension

Microsprinklers

Microsprinklers function on the same type of system as drip irrigation and can sometimes even be combined with drip systems. Instead of small openings that drip water on a small area on the soil, microsprinklers spray a small volume of water over a set radius. The sprinkler heads are typically only a few inches above the soil and therefore apply the water at the base of the plants. Some systems allow you to switch out sprinkler heads that spray in different patterns and distances. One such system that I’ve used has sprinkler heads for patterns from 90 to 360 degrees and from one foot to ten feet in diameter.

This microsprinkler has an adjustable head to apply water in a 1 to 5 foot diameter.

While not as efficient as drip, microsprinklers are more efficient than other systems due to low water volume and consistent pressure throughout the system. They can be more flexible than drip irrigation in settings like landscape beds and around trees and shrubs since one emitter can water a larger area with less tubing and fewer parts.

Soaker hoses

Soaker hoses are popular because they are plug-and-play. You can just attach them to your faucet and don’t have to worry about cutting and assembling tubing and parts. Water is released through the surface of the entire hose, making water application much less precise that drip and microsprinklers as well. Keep in mind that soaker hoses don’t have pressure regulation like drip and microsprinkler systems do so you’ll often find inconsistent watering when you use them. More water leaves the soaker hose at the end closest to the faucet and less (or none) at the far end. The result is usually excess water in some parts of the garden and not enough in others.

Soaker hoses also release a much higher volume of water than drip and microsprinkler systems, which can result in overwatering and water waste. I learned this from experience when I accidentally left a soaker hose running for about three days. The garden was nicely flooded and the water and sewer bill topped out at over $500 that month.

Sprinklers

Sprinklers are probably the most common irrigation system used because of their simplicity. Home gardeners might use the hose-end individual sprinklers purchased at the garden shop which can quickly water a large area. And many homeowners, especially in areas where there isn’t rainfall sufficient to support grass growth, have sprinkler systems installed in their lawns. However, sprinkler systems are only around 65-75% efficient. Spraying water in to the air, especially on hot and dry days, reduces efficiency through evaporative loss. Sprinklers are also less precise in where you can aim and apply water. There’s also the added issue that overhead application of water can lead to or worsen plant disease issues by making conditions favorable for the spread and growth of fungi and bacteria. If possible, use sprinklers only on a temporary basis like establishing new plants or make sure they are calibrated effectively.

Hand watering

While hand watering probably uses a smaller volume of water than sprinklers and you can direct water more precisely, there are still issues with evaporation and overhead watering. In addition, hand watering is usually less effective than other methods because humans are impatient and actually don’t water long enough. Most plants will benefit from a long, deep watering but many gardeners will only give a pass or two with a water hose and will underwater plants. This can cause roots to accumulate in the upper layer of the soil and increase long-term water needs of the plant. Rely on hand watering for temporary needs like plant establishment or container plants (though you can use drip and microsprinklers in containers as well) and use a more efficient strategy long term.

I recently worked with a local community garden to install several thousand square feet of drip irrigation. The system will save them many hours of hand watering labor each week.

Wrapping it up

There are a number of ways you can manage the water needs of your landscape, from renovating your landscape with more water efficient plants to making more efficient use of water through effective and efficient irrigation systems. As more and more cities and states across the US place restrictions on water use having several irrigation tools in your toolbox will be helpful. Always remember that the best strategy is to grow plants suited to your environment to reduce water use in the garden. And in places where there isn’t sufficient water for grass to consider removing lawn and replacing with native vegetation and xeriscaping. Irrigation systems can help in areas with unexpected drought or weather issues but for long-term sustainability gardeners in drier climates should adapt their properties where they live.

Other Sources

Drip Irrigation

Crop rotation makes the garden go ’round

You might have heard of the concept of crop rotation, or even have had someone tell you that you should be practicing it in your home garden. But does this practice developed for use on large-scale farm fields work for small-scale home gardening or backyard farming? And if so how do you even do it? Let’s take a quick look at the practice and learn how you might implement it in your own garden, no matter the size, if it is practical to do so.

The Benefits of Crop Rotation

The benefits of crop rotation touted to home gardens for annual fruit and vegetable plants focus mainly on Integrated Pest Management. Keeping certain crops in one spot in the garden year after year can lead to a build up of plant disease microorganisms and insect pests in that area. These findings are largely based on large-scale production systems, like where whole fields that are hundreds of acres are grown as the same crop and switched from year to year. But there still is some benefit for the small-scale gardener, especially with disease build up from soil-borne diseases or debris left in the garden.

The benefits are less clear for insect pests. Sure, there might be fewer insects that move from spot-to-spot or bed-to-bed in your home garden, but we must remember that insects can fly and a journey of a few feet from one raised bed to the next might not be much of a barrier. It is sort of like when people ask us if using grub control in the lawn will control Japanese Beetles in their garden. There will likely be a small reduction in the population, but we remind folks that Japanese Beetles can fly pretty good distances, so control will be minimal.

Crops in rows and beds can be easy to rotate.

Benefits of crop rotation lay below the soil. Different plants use different ratios of nutrients and some even add nutrients to the soil. Legumes have nitrifying rhizobia bacteria that colonize their roots in a symbiotic relationship and there is a net nitrogen increase in the soil after legumes such as beans, peas, alfalfa, or clover have been grown. That’s why one of the major crops added to crop rotations in the “corn belt” is soybeans (or just “beans” if you’re from around these parts). The soybeans contribute nitrogen to the soil, which helps in the production system because corn is a heavy nitrogen feeder. This is especially true if the roots are left behind or if the legume is incorporated like a cover crop.

Given that crops uptake nutrients in different ratios and that some input nutrients into the soil, by planting the same crop year-after-year in the same spot you can end up with nutrient imbalances, especially in raised beds or small plot areas. Using cover crops and incorporating them into the soil is another facet of crop rotation that can build soil organic matter and address nutrient issues. Fertility can also be adjusted with fertilizer and compost, but using rotation will help with overall management.

Rotating in root crops like carrots, radishes, and turnips can also allow for some good soil aeration, especially in no or low till garden situations.

There’s also research that shows that different plants exude different compounds, like sugars, etc. that attract and feed different microorganisms and rotations which help increase the diversity of the microbiome in the soil. This will not only improve the soil ecology in your garden, but a healthy microbiome can compete with some disease-causing microorganisms to reduce the likelihood of soil-borne disease. Most of us have been told that eating cultured yogurt increases good microbes in the gut and can reduce the likelihood of some illnesses- its kind of like that, but for plants.

How to rotate crops (especially in small gardens)

While crop rotation might not solve all the world’s problems or your garden insect issues, there are still definite benefits to the practice if you can manage it. For some people garden space is too limited. How do you rotate crops when all you grow is a few tomatoes in the corner of a flower bed? Other than putting them somewhere else every year, there isn’t much you can do.

If you have a large garden and especially if you have one that’s a larger tilled-up spot (don’t get me started on tillage), you should definitely be implementing rotation. While I typically garden in raised beds, that usually makes it easy. Crop rotation usually occurs by plant family, so plant families rotate to a new bed each year (more on plant families in a bit).

In general, a crop rotation plan should mean that plants from the same family aren’t grown in the same place in the garden for at least four years if possible. If I plant tomatoes in “Bed A” in my garden this year, then I shouldn’t plant them in “Bed A” again for at least four years if possible. If you’re not growing in beds, then should rotate by rows or by areas of the garden.

Is this practical for every gardener? No. So I say do what you can. If you have a small space and only grow a few things and want to rotate crops, you can do so by time rotation – growing different crops each year. Or adding some container gardening to the mix and rotating crops into containers in different years. As a side note, using containers can be an effective way to rotate crops because you don’t necessarily need to rotate the plants if you can rotate (replace) the soil from year to year (or at least replace the top layers).

Crop rotation can also aid in succession planting. For example, I don’t follow my beans with corn, I follow them with garlic, which is also a heavy nitrogen feeder and works right into the garden schedule to be planted in October after the beans are done. I’ll often do lettuce or leafy greens in a bed in early spring, then thin them out to plant in tomatoes or peppers when the time comes. Incorporating intercropping where you plant different sized plants around each other, like my lettuce and tomatoes, can also be an effective addition to crop rotation.

For a good crop rotation, you’ll want to plan. This would involve sketching/mapping out your garden or at least labeling different beds or spaces. Then creating a chart for each space where you list what crops will be grown there for the next several years will help you plan out to make sure you are giving ample time for the rotation process.

Keeping it in the family

Family members share lots of things and plant families are no different. Not only do some crops look similar but they can often share the same diseases. Keeping families in mind planning crop rotations is one of the easiest methods to keep track of which crops to include in a rotation. For small gardens it might make sense to keep members of the family together. For example if I only have four beds, I would want all the family members together so that I can have a true four year rotation. In larger gardens, realizing that crops are in the same family will help plan out for rotation of multiple crops.

Also keep in mind that some crops will overwinter (depending on where you are) so a fall crop might also be a spring crop in the same bed the following year. Some crops are also biennial depending on your local climate. For example unless you live in an area with winters cold enough to kill them, swiss chard, onions, and other crops will survive the winter and grow the following spring. I typically leave most perennial vegetables like asparagus and rhubarb, as well as perennial herbs like oregano and chives, out of rotations and put them in their own specific place in the garden (or elsewhere) since they don’t need to be replanted every year.

I’ve put together a list of common annual crops by family, as well as an example crop rotation plan for single garden bed/area. As an example, if I had four raised beds I would use this plan for each bed, starting in a different year for each bed so that I grow all the same crops each year, just in different beds.

Common crops by family. Developed from UF/IFAS Extension

A crop rotation plan I might use in my own garden. If I had four beds, Year 2 crops would be Year 1 crops for bed B and so on.

In conclusion…

Crop rotation isn’t an end-all, be-all garden practice. If you can institute some sort of rotation in your garden you’ll likely see long-term rewards. However, if it isn’t possible or seems like too much work just remember don’t plant things in the same place year after year if you can help it. Any rotation, even if it is hit or miss, will be beneficial.

Sources

Benincasa, P., Tosti, G., Guiducci, M., Farneselli, M., & Tei, F. (2017). Crop rotation as a system approach for soil fertility management in vegetables. Advances in research on fertilization management of vegetable crops, 115-148.

Sasse, J., Martinoia, E., & Northen, T. (2018). Feed your friends: do plant exudates shape the root microbiome?. Trends in plant science, 23(1), 25-41.

Wright, P. J., Falloon, R. E., & Hedderley, D. (2017). A long-term vegetable crop rotation study to determine effects on soil microbial communities and soilborne diseases of potato and onion. New Zealand Journal of Crop and Horticultural Science, 45(1), 29-54.

Yasalonis, A. (2019) A must do in gardening: Vegetable crop rotation (UF/IFAS Extension). UF/IFAS Extension (blog)

You gotta know what to sow and what to plant: Veggies and Herbs

As a continuance of my Kenny Roger’s themed article last month on sowing and planting at appropriate soil temperatures, I thought this month I’d approach “Know when to sow ‘em, know when to plant ‘em” in a different way. When it comes growing vegetables and herbs, many new (and even experienced) gardeners are confused as to which plants you should directly sow into the garden and which ones you must transplant.

Of course, some of these recommendations might change based on where you are and your local climate. These are general recommendations based on common practices in most of the U.S. Decisions can be easier to make if you know the reason WHY some things are started indoors and transplanted outside and some things are directly sown, so we’ll start there.

Why transplant?

For the most part, the crops that we start indoors (or purchase at the garden center) and transplant outside are things that either require a long time to reach maturity or require higher temperatures to germinate and thrive than are available outside in regions where these crops are not native. Starting indoors allows us to overcome shorter growing seasons and get those crops to mature in a timely manner.

Many of the warm season crops, such as tomatoes, peppers, and eggplant would likely not make it to maturity if they were directly seeded in the garden after the danger of frost has passed. And while many cool season crops like the Cole crops (broccoli, cauliflower, cabbage, etc.) thrive when air temperatures are cool, they actually require warmer soil temperatures for germination and would be difficult to direct sow outdoors for a spring planting. In many parts of the country, cool season crops do much better as a fall crop since temperatures get cooler as the crops mature. This means that they should be sown or planted in July or August for most areas. Directly sowing of seed in the garden is technically possible at that time BUT there are many challenges including keeping the seedlings from drying out in the hot, dry summer weather. So it is usually still easier to transplant, but you can start the transplants in pots in a protected outdoor space rather than indoors if needed. Keep in mind that several of the herbs don’t start well from seed, so you’ll need to buy transplants (which are usually started from cuttings) or take cuttings from an existing plant.

Why direct sow?

There are a number of crops that grow fast or easy enough that they can just be sown directly in the garden. My personal philosophy is that if it can be direct sown you don’t have to worry about the expense or trouble of starting plants indoors or the expense of buying individual plants at the garden center. Crops like lettuce, beans, peas, corn, squash, and melons are typically very easily sown outdoors. Some folks might opt to start these inside or to buy starts to make it easier, but this is usually at an extra cost that isn’t necessary for success.

Of course, root crops like carrots, radishes, turnips, and beets aren’t easily transplanted because the process of transplanting can damage the root, which is the part you’re trying to grow. Some herbs like cilantro don’t tolerate root disturbance well, so it is best to direct sow as well.

Knowing when to sow is important as well. Cool season crops like lettuce, radishes, carrots, and other leafy greens and root crops can be sown well before last frost (see my article from last month, linked above).

The other thing to keep in mind when direct sowing is that conditions outdoors aren’t as stable as those indoors, so you’ll have to monitor the weather for rapid swings of temperature and also make sure things stay appropriately watered.

Some crops can go either way

While some crops like squash and cucumbers are easy to direct sow, there might be times when growers might prefer to start indoors (or buy starts) and transplant. Crops like melons often require high soil temperatures to germinate, so in places where the soil temperature is slow to warm transplanting might be helpful. Transplanting can also give the grower a leg-up on getting things to maturity quickly. Transplanting is most common for crops where you need a smaller number of plants (like squash and cucumber) but isn’t as practical for crops where you need larger numbers of plants like beans and peas. Keep in mind that crops like cucumbers and squash usually start pretty quickly and will be transplantable after just a few weeks – growing them indoors until they are bigger isn’t necessary and will not create an advantage to getting them to mature quickly.

What to transplant

Broccoli
Brussels Sprouts
Cabbage
Cauliflower
Celery
Collard Greens
Eggplant
Kale
Kohlrabi
Lavender
Oregano
Peppers
Rosemary
Tarragon
Tomatoes
Tomatillos

What to Direct Sow

Beans
Beets
Carrots
Cilantro/Coriander
Dill
Leeks
Peas
Radishes
Spinach
Sunflowers
Turnips

Which Can Go Either Way

Basil
Bok choi/Pak choi
Cantaloupe
Chard
Cucumber
Fennel
Lettuce
Melons
Mint
Okra
Onions
Parsley
Pumpkins
Watermelon
Squash
Zucchini

Sources

Master Gardener volunteers transplant tomatoes for the All America Selections trials in Omaha.

Don’t be a garden gambler: You’ve got to know when to sow ’em, know when to plant ’em

For many gardeners around the US (and the northern hemisphere) the weather is warming up for spring planting season and many are itching to get out in the garden. But when is the right time to plant those veggies and flowers and not gamble on their success? Just like Kenny Roger’s character in The Gambler, knowing when to do something is important (this is where I’ll end the cheesy comparison – you’ve just got to come up with a catchy title sometimes).

I’ve spoken previously on this blog about understanding frost dates, which is important for planting warm-season crops like tomatoes, peppers, and cucumbers that won’t survive a frost. (You can read that article here.) But another temperature factor we must consider, especially for cool season plants that we plant BEFORE last frost is the soil temperature.

Soil temperature is especially important for direct sowing seeds in the garden, but it can also affect the success of transplants planted in the garden. For transplants, having an appropriate soil temperature supports root growth and development and helps plants get established faster.

Many warm season plants, especially plants like peppers, won’t establish easily or thrive unless soil temperatures are sufficient for root growth.

Why soil temperature matters for seeds

For direct sowing of seeds, soil temperature has a major effect on the speed of germination, which also affect the success rate of germination. Each different seed has a different optimum temperature for germination. If the soil temperature is below, or above, that level then germination can be slowed down. Slow germination can decrease germination rates through a few different avenues:

Germinating seeds are vulnerable to infection or decomposition by fungi and bacteria in this soil. When starting seeds indoors, this can be limited by using a sterile seed starting mix. But when direct sowing outdoors, there are any number of fungi and bacteria in the soil that will decompose a struggling seed/seedling. Some seeds sold for large-scale production will have a coating of fungicide on them that will provide a few weeks worth of protection. You won’t likely find this on home garden seeds, but it might appear if you buy seeds from a farm supply store or a catalogue that caters to farm-scale producers.
Seeds have a finite amount of stored energy. Once germination begins, the respiration rate of the embryo in the seed radically increases. If germination is slow, the embryo can expend the stored energy before the seed leaves emerge and start producing energy to support the developing seedling. (This also occurs if you plant the seed too deeply).

Below is a graphic I made for Nebraska featuring the best soil temperature range for major vegetable crops (notice how it also lines up with last frost dates). Just ignore the info on frost dates for Nebraska, unless you live in Nebraska.

Most of the resources you’ll find on soil temperature and germination are for vegetable crops. If you are trying to start seeds of ornamentals, you’ll likely have to find the information yourself. The seed packet will give you some indications of when to sow (before/after frost, or maybe in the fall for overwintering to break dormancy) and you can search online for guidance for specific plants. For info on starting seeds indoors, check out this previous article I wrote on the subject.

How to measure soil temperature

Of course, the tried-and-true old fashioned way is to use a thermometer. You can find a soil thermometer at many garden centers and retailers. You’ll want a soil thermometer because the ones for your kitchen likely don’t have the right temperature range – we’re measuring well below the temperature of a roasted chicken here. Instert the thermometer two to three inches into the soil and wait several minutes for the temperature arm to adjust before reading. Also keep in mind that temperatures fluctuate with the weather and throughout the day depending on temperature and the amount of direct sunlight hitting the soil surface – so you want to measure a few times to make sure the temperature is staying within the right range.

Now, the new technological way is to find a soil temperature monitoring station online. Soil temperature monitoring is a common feature of many weather stations these days and data is more available than ever. Many university extension services or ag research centers compile soil temperature maps for use by farmers and this data is also often accessible through NOAAA or weather.gov. In Nebraska, we have an extension program called CropWatch that provides average daily and weekly soil temperatures year round. We also have a weather station with soil temperature probes at our extension office (perks of having a meteorologist as a master gardener volunteer) and we (and our master gardeners) use it when providing information to clients. It can be hard to find a resource that provides soil temperatures nation-wide to share in the patchwork of private and public stations (and the National Weather Service site can be notoriously hard to navigate). There are a few online resources from the ag industry that provide a country-wide system, like this one.

And now its time for me to walk away, time for me to run

Unlike The Gambler you don’t want to wait until after the plantings done to count your money, er, check the temperature. Remember that knowing the soil temperature, whichever method you use, will help your plants succeed in the garden. If you do, your garden could pay out bountiful winnings all through the season.

By knowing the soil temperature, your seeds will turn into a sure bet. Source: Wikimedia Commons

Home Greenhouses III: Basic Structure Types

Over the last few months I’ve had the chance to talk about the popular topic of home greenhouses. We covered a few of the basics in my first article, then touched on some regulations that might effect the building and management of home greenhouses in some areas. In this installment we’ll talk a bit about common structures used for home greenhouse construction so you can consider which structure(s) might be right for your situation.

Types of Structures

Greenhouse structures can range from simple to the very complex. While home greenhouses tend to fall on the simple construction side, there are still varying degrees of complexity within structures. Greenhouse structures can be put into a few main categories that we’ll cover below. The key to home greenhouse success is picking the structure that works best for you, your situation, and your budget.

Lean-to structures

Lean-to structures get their name from the fact that they “lean” on something for support. Not in a literal sense, but in a sense that another structure, usually a house or maybe a storage building, provides at least one structural wall. A common lean-to setup would have a three-sided greenhouse structure attached to the side of a house or another building. This could range from a structure that is a few square feet for starting seedlings in the spring up to a full-size greenhouse attached to the side of a building. A sun-room, if equipped for starting plants, could be considered a lean-to greenhouse (at least it would at my house, since it would be primarily for plants). This type of structure can be cost effective. You reduce the amount of greenhouse surface you have to build and cover, unless you have special issues for connecting it to your home or other structures (like foundation issues, siding that is hard to attach to, etc). You do want to make sure it is done right especially if attached to your house so you reduce the chance of damage to your home.

A quick search finds many lean-to greenhouse kits available, from small to large and every size in-between.

One benefit to a lean-to is that it can use the wall it is attached to as a heat sink – the wall absorbs heat through the day and then slowly releases it at night when it is colder. If you have a large lean-to greenhouse that serves almost like a sun room you also add functional space to the house where you can enjoy the sun on warm winter days. The heat generated by an attached greenhouse can help provide warmth for your home in winter or at least provide some extra insulation. But it can also result in excessive heat gain in the summer. Lean-to greenhouses are also protected a little more structure wise – they use the building they are attached to for structural support and can often withstand weather, like high wind, a little better than free standing structures.

Free standing structures

Simply put, a free-standing structure is one that isn’t attached to another structure. It stands on its own structural framework. There are a few different options we’ll talk about here which will be further expanded in future article installments on different types of materials used.

Hoophouse greenhouse

A hoophouse greenhouse is built out of the same structure used for a high tunnel or hoophouse. It consists of framing made by bent metal pipes and is covered with polyethylene plastic sheeting. A high tunnel greenhouse would have heating, ventilation, and watering equipment added and would therefore require connection to electric, gas, and water utilities (see my previous article about what this means for a greenhouse being a taxable “permanent” structure). You may also pour a concrete slab for the floor of a hoophouse-to-greenhouse conversion, but gravel or any other floor covering is fine as long as it provides a stable surface and weed control. The “greenhouse” that I inherited from the previous homeowners was left with bare ground so they could plant it like a conservatory.

While these may not be the most attractive greenhouses, they are usually a more cost-effective option for a high-quality, efficient greenhouse. Initial construction costs will likely be lower for a comparable quality framed greenhouse though the polyethylene covering will need to be replaced every few years as it becomes more opaque and light transmission reduces.

Free-standing structures

When envisioning a greenhouse, many people envision this type of greenhouse – one with straight sides, built with a frame covered in solid material. These are definitely more attractive than hoophouse greenhouses and can add an attractive feature to your yard. The most common way for home gardeners to build a free-standing greenhouse is through purchasing a kit. There are a myriad of kits available online these days, of varying prices and qualities usually depending on the materials used in the construction. The kits can be complex but set-up is usually pretty easy to follow though you might want to factor in the cost of hiring a contractor to help with the construction on a bigger kit. Most often these kits need to be built on a concrete foundation or pad so you’ll want to consider the cost and logistics of pouring the needed support. And you’ll also want to think about the utility connections to the greenhouse.

A frame built greenhouse. You can buy kits to build structures like this yourself, or you may want to hire a contractor to help if you aren’t handy. I saw this one at a community urban farm in Trenton, NJ.

Ridge and furrow greenhouses are framed greenhouses that are built together in tandem. These structures are usually used only in large-scale commercial production, so I’ll skip those for home greenhouses.

Geothermal greenhouses

Geothermal greenhouses are gaining in popularity, mainly because people are excited about reducing the need for using electricity or gas to control the temperature. And I say reducing, because in extremely cold weather there will likely still need to be supplemental heat. These structures are definitely different than your standard greenhouse. These structures are usually sunken into the ground to take advantage of insulation by the soil and also the constant geothermal temperatures. There is also usually a high solid wall on the north side of the structure, with a slanted roof made of light-passing material that faces to the south. This allows maximum light to enter the structure and allows that light to heat the solid wall to hold and release it during the night when it is colder. There is also usually an air intake in the ground a few hundred feet away that allows for the pulling of air through a tubing system to warm or cool the air with geothermal temperatures, depending on if it is cold or hot outside.

This geothermal greenhouse project is run by the North Platte Natural Resource District in Scottsbluff, NE. Note that there is a solid wall to the right (with trees growing against it) and that the ramp leads UP to the ground level. The floor I’m standing on in this picture is about 6-8 feet below the ground surface. In addition to standard fare, this greenhouse grows citrus, pomegranates, and figs in one of the coldest parts of Nebraska.

A walpini greenhouse is a specialized/rudimentary style geothermal greenhouse that is sometimes referred to as a pit greenhouse. Instead of building a structure, it is constructed of a pit dug into the ground and covered with a transparent roof. While they sound simple, there are several drawbacks to these structures. One – they don’t do well in wet areas or areas with high water tables, for obvious reasons. Secondly, they were initially designed for use in areas near the equator with the sun almost directly overhead. To function in latitudes far north or south you almost always have to build up a wall on one side to slant the roof cover toward the sun. And even then it is unlikely that light will reach the floor of the structure where plants are growing.

Summary

There’s a lot to consider when picking the type of greenhouse structure for your home greenhouse. There’s often a trade-off between cost, quality, and aesthetics. Options range from the simple to the complex in terms of size, structure, and function. So think about the goals you have for your greenhouse and consider the many different options available to you.

Sources

https://aggie-horticulture.tamu.edu/ornamental/greenhouse-management/greenhouse-structures/

https://extension.uga.edu/publications/detail.html?number=B910&title=hobby-greenhouses

Home Greenhouses Pt. 2: Regulations & Restrictions

Last month I dipped into some of the considerations of owning or building a home greenhouse, having just “inherited” a greenhouse with my new house. The questions and comments were numerous, so I decided to continue on discussing considerations for home greenhouse ownership and operation. There will likely be a few more articles down the line….so strap in.

This time around, I thought I’d talk about something that we hate to talk about, but is important to understand: rules and restrictions around what you can and can’t do, especially if you live in an urban area or municipality.

I know, I know. We all just wish we could do whatever we want, but when we live in close proximity to others there are usually some sort of rules we have to follow to keep the peace. I have a little better understanding of how it works, now that I helped write an urban ag ordinance with our city planning department (fingers crossed is passes city council next month!) that will “decriminalize” urban farming, including controlled environment ag structures like greenhouses. Of course, aside from what you can and can’t do there are tax implications that you should be aware of, no matter where you live (more on that in a bit).

Zoning, Ordinances, and Planning Commissions – oh my!

Most agricultural activity, which includes greenhouses, is likely regulated to some extent if you live within a municipality. Even if you don’t live in a town or city, there could be certain building codes or ordinances on county or state levels that you’ll want to check into.

You’ll want to look up your municipal code online, or call your municipal administration (like city hall, mayor’s office, planning office, etc.-whatever you have) to see if there are specific allowances or restriction for or against greenhouses. There are a few scenarios that could play out here, so you’ll want to be prepared on how to proceed. In general, you might find that greenhouses are:

Permitted, but only in certain zoning areas (more on that later)
Permitted, but requiring a permit of some sorts
Restricted altogether
Not mentioned at all

If you fall in that last category, then anything you do will exist in a gray area, where it isn’t strictly legal or illegal but the fate of your greenhouse (or any fines you might incur) would be up to interpretation by whoever is in charge of compliance (and what side of the bed they woke up on that day). And your greenhouse could be made legal or illegal at any time in the future if some sort of ordinance or decision is made. In the case of our new ordinance here in Omaha, greenhouses and structures like high tunnels will be allowed, but only in certain zoning areas. People who already have structures (and have for years) will now find that those structures are either allowed or banned (or will require a permit). Of course, enforcement of issues like this are often complaint-based, meaning that the municipality probably isn’t driving around looking for your greenhouse but if you and your neighbor aren’t on good terms they can call and turn you in.

As for zoning, there are several different categories and sub categories. The ones you’re most likely to encounter are residential, commercial, industrial, and agricultural (there are others as well). And then there are usually numeric (or named) sub-zones within those zones denoting the density or intensity of use on those zones.

For example R-1 (Residential 1), might be for a single-family dwelling whereas R-3 would be for a small apartment building. C-1 (Commercial-1) might be for a single-use building like a stand-alone fast-food restaurant and C-8 might be for a skyscraper office headquarters. Municipalities use these codes to denote what is and what is not allowed in certain places. For example, the code we worked on for Omaha allows certain types of farming on all residential zones with a conditional use permit and on commercial zones without a permit. (Home gardens and even community gardens are not considered farms and are allowed on all residential zones without a permit.) Many municipalities may also have agricultural zoning on properties around the periphery but still within the city/town limits. On lots like this, most agricultural practices are allowed.

Three things you can do with NYC's new zoning and land use map - Curbed NY — Your municipality may or may not have a map available showing lot zoning, like this small area of NYC.

Since a greenhouse is a structure, there may or may not be a requirement for a permit for the structure, even if it is allowed. This could be dependent on a number of factors, including whether it is considered a permanent or temporary structure, whether there are utilities going to it (which is usually the case for a greenhouse), or even how the structure is constructed. In some areas, it comes down to how pretty or ugly the city and your neighbors think the structure might be. In discussions for our ordinance, there was talk of not requiring a permit for a greenhouse but requiring permits for structures like high tunnels/hoophouses because there’s an (incorrect) assumption that greenhouses are prettier than high tunnels. But many people make greenhouses out of those structures (the greenhouse I inherited is just a high tunnel with a space heater). There was also an assumption that a greenhouse wouldn’t have loud, flapping plastic but a greenhouse would (I kid you not).

The tax man cometh….for your permanent agricultural structure.

One other thing you’ll want to consider about a greenhouse has to do with the tax bill. Since greenhouses are considered permanent structures, many places consider them a permanent improvement to your property and will add them to the tax bill like they might do an out building or garage. The municipality will definitely know about it if you have to apply for a permit or if you get a visit from the assessor. But this could also be dependent on how your structure is built. If you build a solid sided greenhouse (one of the nice looking ones) with a concrete slab floor, permanent utilities, etc then it will definitely considered permanent. But if your structure is more like a high tunnel/hoophouse like mine (a high tunnel in a trench coat pretending to be a greenhouse) then it could be considered a temporary structure and not taxable.

My high tunnel parading around like a greenhouse

High tunnels are considered temporary since you could really take them down at a moment’s notice (and some planning department officials think this means that you take them down and put them up each season, despite how much an extension educator tries to convince them otherwise….but I digress). So your mileage may vary depending on your local rules and how your structure is constructed.

So what home greenhouse topic should we cover next? I’m sure there’s plenty of questions out there – be sure to leave them in the comments. Also – would you like to have your greenhouse featured in a future article (this means I don’t have enough home greenhouse pictures)- feel free to send them to me at john dot porter at unl.edu.

So you think you want a home greenhouse, do you?

Given the growth in home gardening, the fervor around houseplants, and the interest in hydroponics and other growing methods, it makes sense that the interest in home greenhouses is also building. Sure, home greenhouses have been a “thing” for a long, long while – from well-to-do folks with conservatories on their estates to the more common and basic home greenhouse in the last few decades. But shifting interests, and more/cheaper options have made home greenhouses more accessible to the masses. The number of calls that I (and other extension folks) get about greenhouses and other controlled climate production methods is increasing. And even retailers like Walmart and Wayfair have greenhouse options on their websites (I know, because my social media and email is filled with ads about them). So let’s explore some of the benefits and pitfalls as well as some of the things to keep in mind if you are considering (or already have) a home greenhouse.

Honestly, it is planted like a jungle. You can’t even walk through my greenhouse.

Now, the timing of my thoughts on this couldn’t come at a better time (or really, I just write these blogs on topics that are current in my life). I just bought a new house and one of the benefits of this new house, aside from less peeling paint, fewer creaky floors, and (hopefully) fewer plumbing problems is that it came with a greenhouse! A real, honest-to-goodness greenhouse. Not a fancy one – its just a heated high tunnel, but it’s a real greenhouse. Apparently, the previous homeowner was enough of a plant geek to not only have a greenhouse, but plant it like a conservatory as well. So it is full of palm trees, citrus trees, and tropical plants all planted in the ground. Aside from everything being planted so close you have to bushwhack like you’re in the jungle it is quite lovely. So my big winter project will be controlling those plants and making room for stuff I want to grow. But I digress…

A few considerations for home greenhouses

There are a lot of things we could discuss about managing a greenhouse, so I won’t go in depth on a lot of things (maybe more articles to come?). But there are definitely several things you should consider before buying or installing a home greenhouse. Here’s just a few of them:

Purposes and uses

First up is to think about how you’re going to use the greenhouse. Will it be for tropical plants (houseplants), for starting seeds, growing produce, or something else? Having the purpose of your greenhouse in mind can help you choose things like size, materials, and more. For example, if you’re just planning on starting seeds in the spring for your home garden you might get away with a small greenhouse that’s just a few feet by a few feet. If you are going to grow fruits and vegetables, keep large tropical plants, or grow on a larger scale you’ll need something bigger. Keep in mind that the bigger the greenhouse, the more it will cost both in terms of materials or installation and in terms of climate control.

Climate Control & Associated Costs

Whether you live in a cold climate or hot climate, you’ll need to have some sort of climate control in your greenhouse. In cold climates, heat is the major factor. In warm climates and during hot spells, cooling and air flow can be major issues. While we think most plants like heat, there’s definitely a temperature sweet spot for plant growth and it can definitely be too hot. You’ll want to be able to control your temps to keep your plants growing best. Many of the kits available from box stores/etc. don’t include a heat source or fans, so you’ll have to either find alternatives or install your own. Amazingly, the greenhouse I inherited is heated with a space heater. This is a cheap, no-frills option but can also be risky. Shorts and fire hazards are risks, of course. But so is failure of the unit and also power outages. I’m not putting my fancy/expensive plants in the greenhouse because I could imagine a power failure during a Nebraska snowstorm with below zero temps killing everything in the greenhouse. I keep an eye on the temperatures in the greenhouse with a smart sensor (left by the previous owner) that sends temperature information and alerts to my phone, but that can only do so much when you don’t have a method to keep the temperatures up.

That space heater is the sole means of heating the greenhouse

Of course, the other hazard will come when I see the electric bill for keeping the greenhouse warm. Even on cold days the temperatures usually warm up on their own with even a little bit of sun, but keeping the plants warm at night is the problem. I have the heater set to keep the greenhouse just warm enough so that the plants aren’t damaged killed (between 45 and 50), so I’m not paying to keep it super warm all winter long.

Of course, using fans to cool or control air flow will be another expense for most greenhouses, as will water. Greenhouses are typically pretty high humidity, but if you have a lot of air flow you’ll need to water more often. Amazingly, my greenhouse doesn’t have vents or fans, but it is small enough that it doesn’t really need them. If it were a big greenhouse, it would require some airflow to keep it much cooler in the summer. Right now, an open door (covered with netting) suffices.

One way that some folks are reducing energy costs in cold areas is by building geothermal greenhouses. These are becoming oddly common in Nebraska. These are a much bigger undertaking than just popping up a kit from a box store in the back yard. You have to dig down deep enough for the ground to aid in temperature control, have to install an underground system to intake and deliver air (to help with temperature control), and usually build a solid block or concrete wall to absorb solar heat amongst other considerations.

Location, location, location

A place to put your greenhouse is also an important consideration. Whether you are an apartment dweller popping a small greenhouse structure on a balcony (it is possible) or someone installing a walk-in greenhouse on a larger property location is important. Some greenhouse structures are lean-to or attach to the house, meaning that you get the added benefit of the heat holding properties of your house siding. I’ve even seen some greenhouses used as sun rooms – which basically is a modern day solarium. If you attach the greenhouse to your house, you’ll also want to have a safer heat source than just a space heater.

This kit greenhouse is much cuter than mine…but it probably costs a whole lot more.

Orientation of a greenhouse can be important for those that are either elongated (like mine) or those that are on the side of a house in terms of sun exposure and temperature control. Square or roughly square freestanding greenhouses don’t have to be as planned out. For greenhouses on the side of the house, you’ll want to place it on the side of the house, or closest to the side of the house, that faces the sun. For the northern hemisphere this would be the south facing wall. For the southern hemisphere this would be on the north wall. However, in warmer climates where over heating may be an issue you might want to place it elsewhere, like on an east facing wall to get morning sun but protect it from the hot afternoon sun. This is, of course, dependent on light levels available to plants, as you’ll want to maximize light exposure in winter.

For elongated greenhouses, a common orientation is to have the greenhouse oriented north to south so that the sun passes over and both sides receive the same amount of light. An east-west orientation will mean that one side will receive more light. In windy areas like Nebraska, orientation is also important to preserve the structure. My greenhouse has a curved or hooped top (sometimes called Quonset style), which allows wind to blow over the structure. If the flat end of my greenhouse was facing into the wind (west), a strong gust of wind could damage the structure. So location and structure play a part in the ability of a greenhouse to weather the storm.

In conclusion?

We’ve covered purpose, climate control, and location in setting up a home greenhouse. There’s plenty more to talk about when building and managing a home greenhouse, so if interest is high enough perhaps I’ll talk more about the topic in future installments. What say you? Is there enough interest to keep talking about home greenhouses and following the adventures of my home greenhouse jungle?

Po-TAY-to, po-TAH-to: Let’s call the whole yam thing off!

As most folks in the US prepare for a Thanksgiving meal, or at least eat more Thanksgiving-inspired fall meals, potatoes and sweet potatoes often play a major supporting role in these most delicious victuals. Whether mashed, smashed, baked, candied, or turned into casseroles or pies, these starchy vegetables are stockpiled in grocery stores and markets in the fall for shoppers to turn into those tasty treats.

But sometimes there is confusion lurking in those grocery aisles and even in the minds of unwary shoppers….enter the “yam”. Wander down the canned vegetable aisle and you’ll see canned yams. Are they the same thing as sweet potatoes? And are they related to the standard potato that you usually mash, bake, or fry? I yam going to set the set the record straight.

First things first, sweet potatoes and yams are two totally different species so they are not the same thing. They’re even in different plant families so they aren’t even closely related. And neither of them are related to the regular old potato. So those “canned yams” at the grocery store are mis-named. They are sweet potatoes. Yams are rarely consumed or sold in the US, except usually though markets that sell specifically African/Caribbean foods.

Sweet potatoes are soft when cooked, thin/soft skinned, usually pretty sweet, and usually orange. Though there are some white-fleshed, less sweet varieties available. Native to tropical regions of the Americas sweet potatoes, or Ipomoea batatas, are members of the Convolvulaceae, or bindweed, family and are closely related to morning glories many of which are in the same genus Ipomoea. These sweet veggies are part of the root structure, so they are modified storage roots that store starches and sugars produced by the plant.

Yams, on the other hand, are white with a hard skin like tree bark, and are usually pretty dry when cooked. There are three main species of yams in the Dioscorea genus, which has its own family Discoreacea. Also tropical in nature, three different species were domesticated independently in Africa (D. rotundata), Asia (D. alata), and the Americas (D. trifida). Yams are monocots, meaning they are more closely related to lilies and onions than they are to sweet potatoes. Also, unlike sweet potatoes, the edible portion of a yam is a tuber, which is structure arising from modified stem tissue.

Piles of yams…that look nothing like sweet potatoes

And just to round out the tater trifecta – the humble potato. Sometimes called a white potato or an Irish potato (which are both bad descriptors for them because they come in many different colors, and while they are a staple in Ireland they originate from the Americas), these versatile spuds, Solaunum tuberosum, are members of the Solanaceae family and are closely related to tomatoes, Solanum lycopersicum. Their morphology has similarities to those of the yam, though, as they are tubers arising from the stem vs being a root like sweet potatoes.

So where does all the confusion come from?

There are various theories on how yams and sweet potatoes got caught up in this mash-up, and I don’t pretend to be an expert here. But the most common theory that I’ve seen is that enslaved African people held in the US south called the local sweet potatoes by the names they used for yams, as the sweet potatoes reminded them of the yam that was part of the staple diet in many African countries. The word yam is derived from nyam, nyami, or nyambi, meaning “to taste” or “to eat” in certain African language dialects. Adding to the story, apparently Louisiana sweet potato growers in the 1930s used “yams” as a marketing name for a new orange-fleshed sweet potato cultivar and the name stuck.

One thing I find interesting is that yam was used to describe orange sweet potatoes when the white fleshed ones (which are less common now) would probably more resemble an actual yam, both in appearance and flavor. In fact, in my travels in Rwanda I ate many white fleshed sweet potatoes, as they are now a major staple crop in many African countries. It is also interesting to note that the refugee farmers in our urban farm programs prefer to grow the starchier, less sweet varieties of sweet potatoes, which often complicates things as they can be hard (and expensive) to find.

Whether you cook sweet potatoes or “white” potatoes for your Thanksgiving feast, now you’ll know a little bit about how each of those crops are different…and you’ll at least know that sweet potatoes aren’t yams.