John Porter

Contain Yourself: Vegetable gardening in containers and small spaces

Given the growing (haha) popularity of vegetable gardening over the last several years, which has gone into overdrive during the pandemic, more and more people are looking for innovative ways to grow in all kinds of spaces. Container vegetable gardening can be as simple as popping a tomato into a bucket, but there are lots of different ways to successfully grow crops in small, mobile containers. It is possible to grow full sized crops in containers, given a large enough container and space to grow. But more and more plant breeders have been developing small and dwarf cultivars of lots of different kinds of crop plants to meet the burgeoning interest in container and small space gardening. Let’s talk a bit about growing in containers, about some of those crops that do well in containers (including some dwarf/small cultivars, and even some design to make those vegetable containers attractive on your patio or porch.

Container Culture

Growing vegetables and fruits in containers follows the same general rules that ornamentals and houseplants follow. We’ve covered several container questions here on the GP blog, which you can find here. Probably one of the biggest questions (and myths) that we encounter is the placement of rocks or other items in the bottom of pots for drainage. It is a common question over on our social media. So to just get that out of the way, don’t do it – it actually makes drainage worse. The only exception might be if you are using a really large, deep pot and need to fill it with something so you don’t have to fill it all the way with soil – but you still need to ensure that the soil is sufficiently deep so that you don’t end up with waterlogged soil in the root zone.

Here are some other best practices to keep in mind:

Use only good quality potting mix, not garden soil, top soil, or “bargain” potting mix. Container culture means that soil needs to be “light and airy” to ensure proper balance of soil, air, and water.

Leafy greens can be grown in shallower pots than bigger crops like tomatoes and peppers.

Choose the right size and shape of container for the job. You have to look at container diameter for the plant size, but also ensure the proper depth and volume of soil to support root growth. Small crops like leafy greens can make do in a shallower container, but large rooted plants like tomatoes and peppers will require a larger volume. For example, you can grow one tomato plant in a five gallon container (if you’re a “thrifty” gardener, this means you can drill some holes in the bottom of a food-safe 5 gallon bucket). But you can also grow 12 carrots in the same size container, given that the soil is deep enough to accommodate the carrots. For a good size and spacing chart for “standard” sized crops, check out this table from UF Extension.
Drainage is a must. Make sure your containers have good drainage holes (and don’t add rocks!). If your containers are in an area exposed to rain, it would be best not to have saucers under them so that they don’t sit in water.
Make sure the containers are food safe. This isn’t an issue if your using just about any purchased container meant for container gardening, but if you’re repurposing containers you want to make sure they won’t breakdown or leach chemicals into the soil. Some plastics will break down in sunlight, but most should be food safe. The one big exception is plasticized (softened) PVC. Hard/rigid PVC is OK, but the softer plasticized versions can release dangerous phthalates when breaking down. You can look for the number 3 in the recycling symbol to know if you have PVC, and if it is soft and pliable don’t use it. Galvanized metal is another risk, as it can release zinc or cadmium into the soil both of which are harmful to humans. This is alarming as metal containers and raised-bed garden kits have been hitting the market and lots of people grow in galvanized livestock tanks. Be sure if you are using metal containers that they are either not galvanized or are sealed (or you create a barrier) if they are.
Make sure the light is right. Growing in containers doesn’t mean that tomatoes and cucumbers will become shade-loving plants. You’ll still need a minimum of 6 (preferably 8-10) hours of full sun for most fruit or root crops. You can grow shade tolerant crops, like most leafy greens, in shaded areas such as covered porches and under trees.
Nutrients are limited to what is in the potting soil, so keep an eye out for signs of nutrient deficiency and fertilize accordingly. Most potting soil comes with an initial dose of fertilizer, but you’ll probably need to add more through the season.
Keep on the lookout for insects and diseases – they still happen in container plants, too.

Little Plants for Big Flavor

It is possible to grow most standard vegetable plants in containers, save for maybe giant plants like pumpkins and some squashes. However, breeders have been developing numerous crops in small, container-ready sized plants over the last decade or so. These cultivars can let you grow more plants in smaller containers. For many, the fruit or harvestable portion is similar to that of the standard sized plant, but for others the edible parts are miniature themselves. These plants are not just cutesy wootsy (though they really are that), but they are also great alternatives to pump variety into any sized garden.

As a trial judge for the All-America Selections program, I’ve had the pleasure of trialing several plants over the last few years that are great for containers, including the 2021 AAS regional winner Pot-a-peno jalapeno pepper bred by Pan-
American seeds. I’m excited that this year, a new trial has been added to the program to specifically trial plants for container growing, so be on the lookout for more container garden winners in the future.

Container-sized vegetables come in all shapes and sizes. Some of my favorites are ‘Patio Choice Yellow’ Tomato, which grows 18 inches tall and produces numerous yellow cherry tomatoes and the 2-ft tall ‘Patio Baby’ eggplant that produces 2-3″ eggplants (both plants are AAS winners). There’s the cucumber with only 3 foot long vines called ‘Patio Snacker’ and a 4 inch cabbage head named ‘Katarina’. You can find a fairly good list on this document I put together for my container vegetable gardening workshop:

Container-Vegetable-ListDownload

Mini varieties of plants have even created some community-driven projects, like the Dwarf Tomato Project that uses a co-op type process where home gardeners are crossing plants in their own gardens to develop new dwarf cultivars of tomatoes.

Vegetable Garden, but make it Pretty

Pretty Kitty Teacup, colorful tubs and trellises, and more: In and Out | Container gardening, Planter trellis, Garden containers — Gardens like this tomato, pepper, basil and flower combo are common on places like Pinterest

Many who grow container gardens like to make attractive gardens to decorate their porches, patios, and decks. Vegetable gardens can range from the utilitarian (like a tomato plant in a 5 gallon bucket) to the beautiful. There are lots of ways to mix plants to get a good container design if that’s what you’re after. Mixing color, shape, and form of plants can be done just as easily with vegetables as it can be with petunias and geraniums. You can add in flowers for extra pops of color as well. All one needs to do is search the internet (especially places like Pinterest) to find ideas for dressing up container gardens. I talk about container designs with vegetables in my recent talk (recording shared below) and the plant list I shared above.

To (direct) sow, or not to sow, that is the question: whether ’tis nobler in the garden to transplant

Most experienced gardeners will tell you what should be started indoors (or purchased) as transplants and what should be direct sown into the garden, but this can often be confusing for new gardeners. Add to the confusion the fact that some plants have a gray area when it comes to what is best, sometimes it depends on the time of year, and sometimes it depends on where you are as to whether what is possible. So if you forget to start your favorite tomato or begonia indoors in time to transplant, do you have options? Let’s explore!

Why start transplants, anyway?

This is a good question. Why do we take the time and energy to start seeds indoors, or the added expense of buying vegetable or annual transplants? There are a few good reasons:

Germination temperatures. Many of the plants that we traditionally start as transplants require minimum soil temperatures of around 60F and have optimum germination between 70F and 80F. Waiting for soils to reach these temperatures, especially in cooler climates, can really shorten the growing season. Vegetable temperatures, via UNL Extension
Extending the growing season. Related to germination temperatures, starting transplants for warm season crops before soil temperatures warm up and before the weather is suitable for planting can have a plant ready to go once those weather conditions are ideal. This can give you a head start of weeks or months over direct sowing.
Ideal growing conditions. Seedlings for many vegetable and annual crops are quite tender and dainty when they first start out and any changes in temperature, water, or even sunlight can cause damage. This is even more important as spring weather is becoming a bit more unpredictable as the climate changes, where temperatures can drop suddenly and the weather can go from rainy to dry (or snowy) at the drop of a hat (he writes as the temps drop to the 30s and 40s from the 70s the previous week and some parts of the state are receiving 6+ inches of snow in late April).

What about direct seeding?

Ease. Many gardeners, especially newbies, find it a lot easier and less intimidating to just hop out to the garden and plop seeds in the soil versus staring seeds indoors. Of course, buying transplants is equally as easy, but that does limit the variety you have available to plant.
Cost effectiveness. Only needing a pack of seeds (or saved seeds) is typically much cheaper than buying transplants or buying the equipment than starting seeds indoors. This allows for much better cost effectiveness for gardeners.
Some things don’t transplant well. Root crops, like radishes, carrots, and beets don’t transplant well because damaging that tiny little root in any way as you transplant can damage the actual harvestable portion of the crop and result in much lower produce quality (or even loss). Additionally, some plants don’t like to have their roots disturbed, even when they’re tiny little transplants. Cilantro and zinnias, for example, don’t do well with root disturbance so if you do want to transplant them you’ll need to start them in large enough containers so that you don’t have to repot them, and then plant them carefully as to not disturb the roots.

So sow, or not to sow? How do I know?

This is a good question. Oftentimes we can take a look at the seed packet and know, but sometimes we don’t have that packet or maybe we want to fudge a little with what we read on the packet. So what is possible, and what is “best practice”?

A newly transplanted pepper, getting a start for the season

Using some of the information we discussed previously about soil temps and growing season, most of those warm season crops you plant that take a while to grow from seed, like tomatoes, peppers, and eggplants should be started as transplants, especially for folks in cooler climates (like most of the US). Same for those summer annuals (if you absolutely MUST grow annuals, I know some people love them and some loathe them). In warmer or topical areas, you may be able to direct sow these crops, but they may still do better as transplants.

Some of the warm season crops, like beans, corn, cucumbers, squash, and pumpkins can be started indoors and transplanted, but it isn’t necessarily needed. These crops typically grow much more quickly from seed and the seedlings are a bit hardier. We also typically grow some of these plants in much larger quantities, making them take up more space for indoor starting and resulting in a bit more work to transplant versus sow. Therefore, it is usually easier to direct sow these crops, but there could be situations (like overcoming weed pressure in the garden or if you have a really short growing season or low soil temps) where you might want to start them indoors.

What about cool season plants? Sometimes the answer to this one is – “it depends.” Lots of the leafy greens, like lettuce and spinach, and those aforementioned root crops can be direct sown into the garden well before the last frost date. If you have a soil thermometer, or a nearby weather station with soil temp probes, keeping an eye for when soil temps get into germination range can signal when to direct sow outdoors. The leafy greens can be started as transplants, but figure out the optimum soil temperature for gemination – for some, like spinach, it may be way cooler than your indoor temperatures can get (unless you keep your house around 45 degrees). For the Cole crops like broccoli, cauliflower, and cabbage, transplants should be started for spring planting, since they still require warmer (75ish degrees) temperatures for germination. However, if you’re sowing them for fall crops you can possibly direct sow them if other conditions, like water availability and low weed pressure, will support good growth in the garden.

There are several resources, like this graphic from Virginia Cooperative Extension, that can help you out. But keep in mind that certain situations may make other options possible. For example, this graphic is for spring planting, so some of the items, like the Cole crops, may have options for direct sowing for fall cropping depending on where you’re located and your local climate.

This info is good for many areas for spring planting, but climate and planting time can change options for some gardeners
Source: Virginia Cooperative Extension Master Gardener Facebook

Holy Hydroponic Houseplants, Batman!: Can you grow houseplants without soil? Yes!

Just when you thought you got the hang of growing houseplants in potting soil (or if you’re a doting plant parent, a special homemade mix someone on the internet told you to use) comes a new trend – hydroponic houseplants! Or, “semi-hydroponic” to use the more technical term that is used when describing the trend. How do you grow houseplants semi-hydroponically? Do they grow this way? But first, maybe we should ask the question – why?

Why grow semi-hydroponically?

I think for most casual houseplant growers, this method is attractive because it is a challenge. Something new to try after you’ve mastered growing houseplants the old-fashioned way. And quite possibly a pandemic project to provide a distraction after being cooped up in the house for months on end. But are there benefits to growing houseplants this way? Turns out, there are some.

Many articles you find on the subject state that semi-hydroponic houseplant growth can be beneficial for those who struggle with chronic over- or under- watering. The media used for semi-hydroponics is a big, porous puffed clay stone called hydroton or LECA (Lightweight Expanded Clay Aggregate, of course we have to have an acronym!). It is used in some hydroponic vegetable (and other plant) production systems. The large pore spaces it creates and the wicking action it does in the container helps keep a balance of air and water for the roots. The #1 leading cause of death among houseplants is overwatering – it creates a lack of air in the potting media, the roots lack oxygen (called hypoxia), and are either damaged or die. This can also make it easier for fungal infections to cause root rots. But how can you stop from overwatering plants if you’re growing them in water? We’ll talk about that in a bit when we talk about the “how to”.

No photo description available. — **String of Hearts (*Ceropegia woodii*) grows on rocky outcroppings, at home on LECA**
Photo: Shelbi Sorrell

There are some houseplants, like epiphytes, that might also benefit from having a media that isn’t like soil. Plants that are used to growing on tree bark, or in rocky environments in their native habitat that might actually perform better in a media that is a large, rough pebble that does kind of resemble the texture or tree bark or stones. There are lots of tropical houseplants that also grow in areas with high levels of large particulate organic matter like chunks of wood and bark. Plants from boggy environments that have high water requirements or grow in a more “mossy” type soil might also benefit.

No description available. — **Rooting of cuttings in LECA**
photo: Sydney Tillotson Sehi

One other application of this method is for propagation of cuttings. Many houseplant growers like to propagate cuttings in water, but this often isn’t the best practice because the water can be depleted of oxygen (causing hypoxia and rot) or become spoiled or soured (and cause infections). Most horticulturalists will recommend propagation in a light media like seed starting mix, perlite, or sand. But keeping water consistent without overwatering is difficult in this situation, and media can also be a vector for disease. The air space and wicking action of the LECA media used for semi-hydroponics can help keep cuttings hydrated without the issues of water propagation. This method is commonly done in clear class containers, so there’s the added benefit of being able to see root growth to monitor progress.

How do you grow semi-hydroponically?

Of course, in this short article we won’t be able to cover every detail, so if this is something you’re interested in trying, I’d suggest some self-study. I’ll be covering some of the basics, but there’s a lot more to learn.

The Kratky Method - Grow Food The Passive Hydroponic Way (Step by Step Guide) | Trees.com — Kratky hydroponic method Photo: UpstartFarmers

First, this method somewhat resembles one of the simplest forms of hydroponic production that lots of home hydroponic gardeners use, called the Kratky method. In this passive hydroponic method, a plant is suspended above a water-based nutrient solution. At first planting, the nutrient solution is right below the plant, close enough for a few inches of the roots to touch the solution. As the plant grows, the roots elongate and the nutrient solution level is reduced to keep just a few inches of the roots submerged. This allows the roots to take up solution, but the space between the plant and the solution allows a majority of the roots to be surrounded by air to avoid the issues of hypoxia.

In semi-hydroponic houseplant growing, a container (usually clear glass, at least for beginners) is filled with the LECA media and the plant’s roots are distributed through the media. (The media should be washed and soaked in water first, to remove dust and allow it to hydrate.) It is easier if it is a young plant or recent propagation so you don’t have too many roots to deal with (you may need to root prune larger plants). Smaller plants will also withstand the shock of going to this system, especially if they’re moving from a potting soil media. (Note: Clear glass container + nutrient solution + light = algae. Be prepared to clean up the algae from time to time.)

A (dilute) nutrient solution is added to the container. The roots should not be submerged in the solution, but rather it should be added to a level where it will wick up through the media to surround the roots. The basic rule of thumb is to fill the container about 1/3 of solution, but if the container is exceptionally large or the roots are very small, you may need to fill it higher to make sure the media around the roots stays hydrated.

This nutrient solution is one of the trickier parts. You can use a general all-purpose hydroponic nutrient mix, available in lots of garden centers now or online. You can also try some of the general houseplant fertilizers or ones specific to whatever houseplant you’re trying to grow. You’ll want one with micronutrients as well as the macronutrients like N-P-K – since we’re growing without soil or an organic matter based media you’re going to have to supply all of the plant’s nutritional needs. You’ll want to mix the solution between ¼ – ½ the recommended strength – you’ll need to see what works for you and your plant. And then you’ll want to pH balance the water to create the right environment for the plant and make sure that nutrients are available for uptake. The pH range for most plants is between 6.0 and 7.0 (aim for 6.5), unless you have one with specific needs. For this you’ll either need pH test strips or a meter (which you can now get for less than $20 online) and some acidic and basic solutions to adjust pH (you can use some household items like vinegar to do this, but your best bet would be solutions specifically prepared for adjusting hydroponic or aquarium pH levels commonly referred to as “pH up” and “pH down”). This pH adjustment is a lot easier (and maybe unnecessary) if you start with distilled or reverse osmosis water (or if you have a really good water filter that removes dissolved solids). The pH levels and dissolved solids in some tap water makes it hard to adjust (my water here in Nebraska is very basic because it is very heavy due to high calcium levels, which also throws off the nutrient balance). Rainwater or melted snow can also work (though may not be pH balanced).

You want to keep the solution topped off so that the media stays sufficiently moist. As with hydroponic production, plants pull nutrients out of the solution at different rates, so you can get build-up of some nutrient salts over time that could result in poor growth and even toxicity. To avoid this, every few weeks (or more often if your plant is a heavy drinker) you might need to perform a flush, where you drain off the nutrient solution, give a quick rinse with tap water, and start over with fresh nutrient solution.

More experienced growers might graduate to using this method in containers other than clear glass. This adds a level of challenge, since you can’t automatically assess the level of nutrient solution by visual inspection. The use of self-watering pots that have net pot or hole-y insert pots are commonly used for this. Or you can buy net pot or orchid pot plastic inserts to use in any non-porous container you desire. Growing in net pots can make the flushing process easier, since you can just pop it out of the container and run tap water through it. Otherwise, you’ll have to find a way to pour the tap water out of the container or

completely remove the plant and wash the media.

What can I grow semi-hydroponically?

May be an image of indoor — **My rescue phalaenopsis**

Well, you can try with a lot of different plants. I don’t know that there’s a list of plants out there for do’s and don’ts, but there are a few good candidates to try. Most tropical houseplants are good candidates. I’ve seen lots of articles on orchids, and I just recently put a rescue phalaenopsis in semi-hydroponics. Other epiphytes like holiday cacti and bromeliads are also good candidates – think of things that like to grow on trees/treebark. Hoya, which are all the rage in houseplant circles, are also candidates due to their mostly epiphytic habits. Lots of tropicals like Monstera, Philodendron, and Pothos also do well in this system.

Things that probably won’t do the best in this system are ones that don’t like to have “wet feet” – I’m thinking mostly desert cacti and succulents. But some of the LECA lovers that I talked to said that some succulents, like “string of pearls” and other strings of things (hearts, dolphins, turtles, etc) do grow well. But if we take a look at their natural habitat, where they grow over rocky outcroppings, it makes sense.

There isn’t really an exhaustive list, so you might want to experiment if you’re wanting to try it out. As long as it isn’t an expensive plant (and there are lots of expensive houseplants out there), a little experimentation can help you find the plants that would work best for you and your situation.

In conclusion…..

Growing houseplants semi-hydroponically isn’t for everyone. Getting everything just right can have a learning curve, especially if you weren’t great in chemistry class. But, it can be a fun way to challenge yourself and may also benefit your plants in the right situations. It is becoming so common that the materials are getting easier to find – many garden centers now carry the LECA and hydroponic supplies, you can always order them online, and you can even find small bags of the LECA/hydroton in the ever expanding houseplant section at IKEA (of all places, if you’re lucky to have one). So if you’re up for a challenge, give it a try! You might find a fun new way to grow houseplants….or a new way to kill houseplants! But the fun will be in the trying.

Special thanks to:

Anni Moira
Sydney Tillotson Sehi
Suzi Sellner
Tiffany Caldwell
Shelbi Sorrell
Maggie Pope

Sources:

Houseplant Hubub: The rage about variegation

It is no secret that houseplants are hot right now. Interest was growing before the pandemic, especially with millennials and younger folks. Then the pandemic hit. Houseplant interest skyrocketed since people were stuck at home and wanted to bring a little bit of nature indoors to make their spaces a little more cozy for 24/7 habitation.

This has caused the demand, and price, of many houseplants to increase, especially if they are on the rarer side. One thing that increases the price of many plants is when a variegated version of a standard plant has been developed.

Just as an example, after posting a photo of my “reading nook/houseplant oasis” in my home office I was informed that variegated form of a Monstera deliciosa vine that I had was the highly sought M. deliciosa “Albo-Variegata” cultivar, usually referred to as a Monstera albo, or just Albo. Folks were reaching out to buy cuttings right and left. I ended up selling 5 single leaf/node cuttings over one weekend and made $675 in the process. That’s right, $675! The most variegated of the leaves sold for $200, and that was actually a bargain price. The garden writer for the local paper, the Omaha World Herald, even picked up the story and shared it as a focus on the four new houseplant shops that have popped up in the city over the last few months.

Had my plant not had the variegation that made it an albo, each of those cutting would have been worth a few dollars apiece. So what makes some plants variegated and others not? Sometimes the variegation is the standard form found “in nature” and sometimes it is a cultivar or variety that has been bred or discovered by chance. Let’s take a look at all the ways that a plant can get that variegation, whether it is standard or rare.

Chimeric variegation

My *Monstera albo* that caused the hubub

This is a common form of variegation and the one responsible for the variegation of my Monstera. In this form, a genetic mutation in some cells changes that cell’s ability to produce chlorophyll. It may reduce chlorophyll production, resulting in yellowish or silver coloration, or eliminate chlorophyll altogether, resulting in white coloration.

The name chimeric or chimeral is based on the fact that the plant displays two (or more) chromosomal patterns on one plant. In Greek mythology, a Chimera is a frightening fire-breathing female monster with the head of a lion, body of a goat, and the tail of a serpent.

Image result for chimera — An ancient chimera statue

This variegation can be stable, where the pattern persists throughout the plant. Or it may be unstable, where it is random on certain leaves and parts of the plant can revert back to the standard green form. These plants can also produce leaves that are almost totally white, which usually results in a leaf that will die since it can’t photosynthesize.

This type of variegation also means that cutting or propagations may or may not be “true” to the pattern. It can be random. For my Monstera, the presence of white striping in or around the node that will become the new plant is the important marker for whether the new plant will be variegated or not.

One common chimeric houseplant is the plant formerly known as Sanseveria, now a Dracena (Snake plant or mother-in-law’s tongue). Many of the different color patterns on some of the cultivars are due to cuttings taken from different parts of the “original” natural type that display different colors on them.

Viral Variegation

While beautiful, this variegation will often reduce the productivity of plants if not kill them outright. There aren’t a lot of houseplants that have this variegation, but some Hosta cultivars do. Probably the most famous case of viral variegation is the Tulip Mania during the Dutch Golden Age (in the 1600s). Prices of tulips skyrocketed and people were buying them as investments (maybe like the current houseplant craze, or GameStop stocks, or bitcoins). Unfortunately, as the virus reproduced plants kept getting weaker and weaker. Eventually the tulip market collapsed and lots of people went broke. Let’s hope that doesn’t happen with the houseplant market….at least with my fancy Monstera.

Natural Variegation

This type of variation occurs when the patterns or colors of the variegation are written into the DNA of the whole plant. It will occur regularly throughout the entire plant, not randomly on some parts as in chimeric or viral variegation. This variegation is passed through cuttings and usually through sexual reproduction from seeds as well, though different variations may pop up that cause a more desirable or rare cultivar.

Common houseplants such as Tradescantia, Maranta (prayer plant), and many more common plants have this type of variegation.

Blister, bubble, or Reflective Variegation

Reflective variegation on *Phildodendron* ‘Birkin’ following veins in the leaf

This type of variegation occurs when there is an air pocket or bubble between the lower layer of tissue and epidermis, or skin, of the leaf. The lower level typically has green pigmentation from chlorophyll and the epidermis does not, resulting in a pattern that is usually white, silver, or yellowish though other colors could appear. This pattern can be blotchy or splotchy like in some types of Pothos and Pepperomia. It can also occur along the veins of some plants, resulting in white or silver veins on green leaves, as in some Alocacia, Anthurium, and Philodendron varieties.

In conclusion…..

Even if you don’t have an expensive plant hiding in the corner, houseplants can add lots of fun and color to your living spaces. And sometimes, your houseplant obsession can even pay for itself. Online swap and sale groups have houseplant afficionados swapping and selling cuttings and plants all over the place. So enjoy your plants….and maybe you’ll find a cash cow hiding in the corner. Don’t mind me….I’m just over here propagating more Albos to fill up my “mad money” jar.

Sources

Variegation mutants and mechanisms of chloroplast biogenesis

Variegated Indoor Plants: The Science Behind The Latest Houseplant Trend

Chimeras and Variegation: Patterns of Deceit

Tiny plants that pack a flavor and nutrition punch: getting in on the microgreen trend

If you do any searching for gardening (or even think about the color green), you’re likely bombarded with adds on social media and search engines about all stuff gardening. One of the recent trends is microgreen production. There’s all kinds of fancy little systems and gizmos that will help you grow microgreens for a price. But what are microgreens? Are they the same thing as sprouts? And do they have the same food safety issues as sprouts? Let’s discuss, shall we?

What are microgreens?

Microgreens are basically tiny plants harvested shortly after germination. Unlike sprouts, like the common alfalfa or bean variety, these baby plants are grown on a medium of some sort and just the “above ground” portion of the plant is harvested. Sprouts, on the other hand, are typically grown in a moist environment without a medium and harvested whole -roots, seed, and all. It is this wet and warm environment that make sprouts especially risky for food borne illness.

Microgreens can be any number of different crops, but common types are kale, mustard, chard, broccoli, arugula, and radish. Sunflower and pea are also common, but they fall more in the “shoot” classification since they are harvested a bit larger. There’s lots of other crops that are used for microgreens, including herbs like cilantro and even marigolds, so the sky is the limit!

Why microgreens?

There are a few things that make them attractive to farmers which also are good for home growers. First, it only takes 1-3 weeks for a finished crop. This fast turn-around makes it easy to keep up with production needs for customers (or your own uses) and also reduces risk. If a crop fails, it is much less damaging if it only took a week to grow rather than a whole field full of peppers that have been growing for months getting wiped out by disease or a storm.

Second, is the value and profit. While there is some investment in seed starting equipment and then continued expenses of seeds, trays, and media, microgreens have a high per pound value. Microgreens are used in small quantities and are therefore sold in small quantities. A small amount you may purchase at a farmers market for a few bucks may be an ounce or less. When you calculate it out by the pound, microgreens are sold for between $20 and $200ish per pound (depending on the variety, organic production, other factors).

And of course, microgreens lend themselves to year-round production. It can be a fun and easy way to get some flavor and color on the plate even in the dead of winter. Just a few square feet of production area can provide a decent sized crop, so it is great for those with limited space or no garden at all.

Look ma….I made fancy mac and cheese. All I had to do was add some microgreens.

Microgreens are popular with home cooks and chefs alike because they pack a flavor punch and add some color and texture with just a pinch or two of product. Studies have shown that microgreens also pack a nutritional punch in a small package. However, production practices can greatly influence nutrient content, especially light. Microgreens grown with higher quantities (brightness) and quality (spectrum colors, mainly red and blue but also green) of light have higher nutrient values.

How do you grow microgreens?

The way you grow microgreens lends itself to why they are so popular to grow, for both home enthusiasts and farmers alike. Microgreens are basically recently germinated seedlings. If you are good at seed starting, you can be good at growing microgreens. Lots of the ads I’ve been seeing recently are for attractive but pricey growing trays and mats that you just lay down and water. However, budget conscious gardeners can grow them pretty simply and inexpensively at home. And you probably have most of the equipment you need, especially if you start your own seeds each year!

Microgreens are usually grown in those flat plastic seedling trays, the type that don’t have cells in them (the ones used to hold the cell packs). For those “in the know,” they’re called 1020 trays. You can either use a sterile media like peat or coir or purchase specific fiber mats (I have some made from hemp -they work well but smell like a moldy gym sock full of weed when in use). We’ll talk about the importance of a sterile media when we talk food safety.

A demonstration of sowing microgreen seeds on hemp fiber mats.

The sowing density of seeds can vary by crop due to seed and seedling size. Typically, one ounce of seeds can sow anywhere from one to eight 1020 trays. In general terms, large seeded crops like chard and beets may take up to ½ cup per tray and small seeded crops like radish or kale might require ¼ cup. Tiny seeded crops, like sorrel may need just a few tablespoons. If you’re really into production, Penn State extension has an excellent Excel calculator to calculate seeding rates. Typically, you’ll broadcast the seeds on top of your media and then maybe sprinkle a little more media on top to make it easy (no dibbler here!).

Most seeds require darkness to germinate, as well as high humidity. You can use humidity domes and cover trays with an opaque material to achieve this, or you can use the trick that producers use and stack trays on top of each other for a day or two. This keeps the seeds covered and dark and preserves moisture and humidity. Just unstack them after a day or two and stick them in their growing location. As with seed starting, you’ll have the most success if you provide some good quality light and heat. (You can search through old articles to find lots of info on seeds starting). There’s research that shows that light is a big factor in microgreen growth, coloration, and nutrition levels.

You’ll harvest your microgreens typically one two three weeks after sowing. Typically, this is done after at least one set of true leaves have formed, but you can usually let them go until there are at least two (or sometimes three) sets of leaves. To harvest, use a sharp, cleaned pair of scissors to snip the seedling off just about soil level, being sure not to disturb the media so that you don’t get it on your precious produce.

There should be no need to wash the microgreens right after harvest and before storage, since they’re typically grown in a clean environment. Washing before storage can increase storage moisture to levels that support microbial growth, reducing storage time and also increasing the risk of human pathogens. Instead, store microgreens (and most leafy greens) without washing and wash just before use.

Working with a local farmer to demonstrate microgreen production at a regional production conference.

Food Safety

As we learned when discussing what microgreens are and comparing them to sprouts, we learned that microgreens have been found to have much lower risk of human pathogens. However, the risk is not zero, especially if production practices are conducive to pathogens. We just discussed that washing prior to storage can lead to microorganism contamination, but there are a few other areas where contamination is easy. To reduce contamination, follow these steps:

Always use clean and sanitized trays or containers. If reusing trays, be sure to wash with soapy water then sanitize with a dilute bleach solution or other approved sanitizer.
Keep the production area clean and sanitized. Microgreens are often produced on multi-leveled vertical racks, so contaminants can drip down. Make sure all surrounding surfaces are clean.
Use sterile media for production. This is typically a soil-less media made primarily of peat or coir, like a seed starting mix, or specialized fiber growing mats. Do not use regular potting soil, any mix containing compost, or anything containing soil to avoid the introduction of human pathogens or other microorganisms that might affect the crop, such as those that cause damping off.
Use cleaned and sterilized seed. Many companies sell seeds specifically for microgreens that have been processed to remove pathogens. I’ve seen seed production, and while it isn’t filthy, it typically isn’t sterilized to the level of food production standards. You can sterilize common seed at home using a solution of hydrogen peroxide or vinegar. For guidance, visit this guide from K-State extension.
Use a clean source of potable drinking water. If you wouldn’t drink it as is, don’t use it. Typically this means it should be straight from the tap of a trusted source.

Conclusion

Growing microgreens can be a fairly easy and enjoyable way to produce something fresh and green year round. In terms of production practices, it is basically ramped up seed starting where your seedlings only grow a few weeks before harvest. This makes it a fairly easy process and one that can be done almost anywhere. If you’re looking for an indoor gardening project or just want to add a quick source of nutrients to your diet, give microgreen production a try.

Sources and resources:

Microgreen nutrition, food safety, and shelf life: A review

Microgreens and Produce Safety

Microgreens—A review of food safety considerations along the farm to fork continuum

A step-by-step guide for growing microgreens at home

Planning Ahead (in a pandemic) for Vegetable Garden Success

Looking back to January 2020, most of us would have never imagined the year we’ve had. All of our best laid plans went away and instead we socially distanced, scavenged for toilet paper, and canceled events and vacations. But one thing that wasn’t canceled was gardening. By June, garden retail sales had increased 8.79% over the average, a big jump for a trend that was already showing increased gardening over the last few years. Wanting to grow food to ensure a safe food supply was one reason gardening increased this year, but it also served as away for people break the boredom of being stuck at home.

One bit of advice that we in Extension always give to gardeners, young and old, is to plan ahead, especially if they are growing fruits and vegetables or starting their own seeds. Given that rapid increase in garden sales, many would-be gardeners were frustrated to find the seed racks and plant shelves empty and online catalog retailers out of stock. From personal experience, I can tell you that white beets don’t look quite as pretty in the jar as those bright red ones. Given the fact that the pandemic is likely to continue well into 2021, it would be a good idea for those thinking about gardening to plan ahead on what they want to grow and plan to buy seeds and supplies early. This not only helps you plan out what you want to grow and when to start or plant it, but will also help you beat the rush and get the plants or varieties that you want.

Here are some things to consider while planning for your vegetable (or other) garden:

What are your garden goals? Are you wanting to harvest for fresh eating only? Hoping to preserve harvest for later? Have extra to sell or give away? Figuring out what you hope to accomplish will help you plan out how to use your space most effectively. Plan to plant extra of stuff you plan to preserve or give away, and plant it all at the same time to have a larger harvest. If you’re focusing on fresh eating for just your family, planting smaller quantities of each plant and spacing them out over time would be better.
What do you enjoy eating or growing? Focus on the crops that you and your family like to eat, especially if you have limited garden space or time.
What resources are you willing to commit to gardening? How much money do you have to invest in seeds, plants, or supplies? And how much time do you have to spend per week? You should base your garden size on what you can reasonably support. And also look for investing in efficiencies. For example, adding drip irrigation will be an investment of time and money up front, but will save on water bills and time spent watering the garden and will likely increase your harvests so it can have a pretty decent return on that initial investment.
Are you planning on growing throughout the garden season? Many people focus on gardening May through September and often miss those very productive early spring and fall months when cool season crops flourish. Making a plan for using space effectively can include growing an early season, summer, and late season crop all in the same spot using interplanting or succession planting. If you aren’t sure what to grow when in your climate, look for local growing guides or calendars to help. Your local Extension office will likely have some good resources to share. Having an idea what you want to grow throughout the season will also help you make early purchases to ensure you have what you need throughout the season. Seeds are usually off the store shelves by mid to late summer, so buy seeds in the spring for those fall and late planted crops just to be prepared.
Are there things you want to grow that would be easier to buy? This question is especially important if you have limited space, time, or money. Crops like potatoes, cabbage, and onions are often cheaper for home growers to buy than grow and crops like squash can take up a lot of room and are often easy to buy (there’s usually plenty of zucchini everywhere in the summer). Focus on those things you can’t buy like interesting varieties of tomatoes, peppers, etc.
Are you ready to deal with diseases and pests throughout the garden season? Be ready to scout the garden for pests and do a little research on the common pests and diseases on the crops you’re growing so you know what to look for. You can often reduce the likelihood of pests and diseases by growing newer resistant cultivars versus older varieties and heirlooms that don’t have resistance bred in.
What has worked (or not worked) for you in the past? Focus on growing those things you do well. Take some time to research or learn how to better grow the things you haven’t grown so well in the past (extension resources are great for this- contact your local office or search for info online, looking for pages that end in .edu). And don’t be afraid to try something new – you can find new favorites by trying out new cultivars or even new crops.

Using some of these steps can help you plan ahead for a year of garden success. The key is to start early, and especially in 2021, buy those seeds and supplies early. When you do, take a look at your plans for the whole garden season and plan accordingly in advance. Though while you’re out there buying those seeds, be sure to leave a packet or two on the rack for me. I’d prefer to have red beets for pickling this year instead of those white and yellow ones.

Hydroponics for the Holidays? Home Systems are a hot holiday gift list item

Systems to grow fresh produce in your home using hydroponics or other automatic processes have been popular for several years but seem to be even more popular this year with more folks home and looking for something to do and hoping to produce their own food. As a result, these systems are popping up on holiday wish lists and gift buying guides all over the internet. But are they worth it? And if so, what should you look for in a system?

First off, what are these systems? And what is hydroponics? Hydroponics is the process of growing plants without soil in a aqueous nutrient solution. Basically, you provide all the nutritional needs of the plants through nutrient fertilizers dissolved in water. These systems can grow plants faster and in a smaller space than traditional soil-based production. It also allows you to grow plants indoors and in areas where you would not normally be able to grow.

This Aerogarden (which is the previous generation) has a digital brain that controls light and water schedules for the specific growth phase of the plant and yells at you when it thinks you need to add more fertilizer solution.

As for systems, you might have seen what is probably the “oldest” one on the market – the AeroGarden. Since it is the oldest and most common, that’s the example we’ll be staying with. It has been around a few decades and has evolved from a basic electronic system to fully automatic, “smart”Bluetooth connected systems that you can control with your phone. In recent years there have been many new systems come onto the market at all different sizes and price points. A quick search of online retailers will usually provide an array of options – from DIY kits to plug-and-play enclosed systems such as “Click & Grow” and “Gardyn”. My only experience is with the Aerogarden system, so I can’t speak to any of the others (though I’d love to try them out!).

The answer to “are they worth it” is up to you, really. Most home based hydroponic or aeroponic systems offer convenience, but at a cost. Most cost several hundred dollars and are small, so they produce a small amount of produce (or other plants) at any one time. So you have to determine what goals you, or your intended giftee, have with the system.

“Baby” lettuce, 18 days after sowing. The current version of this 9-plant Aerogarden system, called the “Bounty”, retails for $300 but you can usually get it for under $200 on sale.

The benefit of the “plug-and-play” enclosed systems like the AeroGarden is that basically you can take it out of the box, set it up in less than 10 minutes, and have some fresh lettuce or herbs in a few weeks. It controls the water cycles, lighting, and all other conditions for growth. You just drop in pods that contain the seeds suspended in a spongy-material. The smallest system, that holds 3 plants, retails for $100. As an additional expense comes from buying refill kits to replant. The mid-size systems are the most common and range from $150-$300. The largest system, the “XL Farm” retails for $600. But these systems are commonly on sale at pretty significant discounts.

For many systems, you typically buy a new set of pods (there are different plant variety selections), but there are pods you can buy to assemble your own using your own seeds. For the AeroGarden, the pod kits range from $15 up to $30 to grow up to 9 individual plants. There are other plug-and-play systems on the market, as well as some kits that are more build-your-own and less automated.

No matter which systems you buy (or gift), keeping these costs in mind is important. If you’re looking for a fun and easy activity with the benefit of a little fresh produce and aren’t as concerned with production costs these systems may be for you – and if you are giving or getting them as a gift that definitely makes it more economical. But given the cost of the plug-and-play systems and the refill pods, they will never be an “economical” option for producing your own food. If you are wanting to produce food on a budget and you’re interested in home hydroponics, look for plans to build your own or buy a DIY kit.

Smashing Pumpkin Myths: Bleaching to extend shelf (and porch) life

Scrolling through social media in September and October and you may see those basic signs of the season: scarves, pumpkin spice lattes, sweaters, and Halloween ideas galore. One of those Halloween ideas is to extend the life of your pumpkins, carved or otherwise, by giving them a treatment with household bleach. Keep scrolling and you might see another post decrying the use of bleach as inhumane and poisoning for wildlife. So which is it? Is bleach safe to use as a sanitizer on your jack-o’-lantern or are you poisoning the neighborhood squirrels? Let’s use our gourd to explore the science.

The bleach acts as a sanitizer, neutralizing fungi and bacteria on the surfaces of the pumpkin that will cause decomposition and rot. Even un-carved pumpkins will eventually succumb to degradation under the right conditions. But if bleach kills fungi and bacteria, will it kill wildlife? The answer is – not if it is used correctly. Bleach, and sodium hypochlorite (the active chemical in bleach) are toxic if consumed directly in concentrated amounts, however, dilute solutions break down quickly in the environment. Products containing sodium hypochlorite, including plain household bleach, are actually approved and labeled for use as a sanitizer by produce farmers to reduce both human pathogens and decomposition microorganisms and extend the shelf life of produce that finds its way to the grocery store, farmers market, and any other avenue from the farmer to the consumer. These wash water sanitizers are used more for reducing cross contamination of from pathogens introduced to the water from dirty produce, but it can reduce the microorganism load on produce items. If used correctly to sanitize the surface of the pumpkins, bleach DOES NOT pose an increased risk to wildlife (or human) health.

What is the proper way to use bleach in sanitizing that pumpkin so that it doesn’t face an early demise?

1) Make sure the pumpkin is clean by washing with plain water or a mild detergent to remove any soil or debris. Sanitizers like bleach are quickly neutralized (used up) on dirty surfaces (this is a good lesson for home cleaning, too – you cannot sanitize a dirty surface).

2) Prepare a DILUTE solution of plain household bleach (unscented, and not “splashless”). The recommended concentration is 200ppm sodium hypochlorite, which you can achieve with 1 Tablespoon of bleach per gallon of water.

3) Apply the solution to the pumpkin using a spray bottle. Alternatively, you can prepare enough solution to dunk the pumpkin(s) and immerse them in the solution. If you are sanitizing a carved pumpkin, I would opt for the spray method – dunking may result in infiltration of the solution in to the exposed flesh. It will still break down since it is a dilute solution, but it will slow down the process since it protects the bleach atoms from air and sun exposure.

4) Allow the pumpkin to air dry. Sanitation is not immediate (keep that in mind for sanitizing surfaces in the home, as well) and wiping can cause cross contamination

If I can do this with a pumpkin, should I be doing this with my other produce?

The short answer is NO. It is not recommended that home grown or purchased produce be washed with any sort of detergent or chemical in the water. Fresh cold water and friction should be sufficient for removing soil and pathogens on the surface. Proper protocols, equipment, and training are needed to make sure sanitation is done properly. Knowing which produce items can and cannot be washed with a sanitizer is important. However, if you are harvesting produce like pumpkins or winter squash for long-term storage you may want to consider sanitation using the above methods.

I don’t want to use bleach, can I use something like vinegar?

There are many sanitizers approved for use by produce growers for sanitation, so bleach is not the only option. For home consumers there aren’t so many options. Vinegar is often mentioned as a wash for produce. I found no direct mention in produce handling guides of using vinegar on pumpkin, but most produce wash solutions use vinegar at a much higher concentration because it is much less effective at sanitation. I found rates ranging from 1/3 c vinegar to 1 c water to 100% undiluted household vinegar for use as a produce wash.

Sources:

Sanitizers Labeled for Use on Produce (Produce Safety Alliance)

Produce Wash Water Sanitizers (UMN)

Guidelines for the use of chlorine bleach as a sanitizer in food processing operations (OSU)

Saving for the Future: Seed Saving Tricks and Tips

As summer winds down and the summer crops and flowers start to slow down many gardeners start thinking about saving seeds. Who doesn’t love saving seeds from that favorite tomato or beautiful coneflower? Not only do you have some for next year, but you can also share with your friends! There are definitely some things to consider and some myths out there when it comes to seed saving, so let’s talk about how to do it right.

You’ll get the most consistent results from open pollinated or heirloom varieties that are self-pollinating. These plants have genetics stable enough that the seeds you save will come out looking and acting like a close approximation to the plants from the previous season (with some variation based on your selection of the “best” plants you save seeds from. Self-pollinating species are: tomatoes, peppers, eggplant, beans, peas, peanuts (note, peppers and eggplants have more open floral structures that can be cross pollinated). Most tree fruits like apples and pears are cross pollinated and they are notorious for not “breeding true” – even if you hand pollinate to ensure that the mother and father are both the same cultivar you’re likely to get surprises. Stone fruits (peaches, plums, etc) are less variable but still not true-breeding. Bee pollinated plants are also notoriously hard to save seed from, since they can cross pollinate with different varieties and cultivars from miles away. It is especially interesting for plants that look totally different but are the same species (like pumpkin and zucchini).

A puccini or a zumpkin? Either way, it tasted nasty.

Myth: You can’t save seeds from those new modified hybrid plants. They’ve been made to be sterile
First off, hybrids aren’t genetically engineered and there are no GE plants available to home gardeners (most home garden crops don’t even have GE versions). Hybrid plants do in fact usually produce viable seeds. However, you won’t get the consistent results you will with open pollinated/hybrid varieties. Hybrids are the F1 generation of a specific cross between a mother and father plant. The offspring from that F1 generation (the plants from the seeds you save) is called the F2 generation will be a mix of traits – some will look like the F1 generation, some will look like the mother, some the father, and some the milkman. So you’ll be in for a mixed bag of surprises. According to our former GP colleague Joseph Tychonievich’s book “Plant Breeding for Home Gardeners” you can even develop a stable open pollinated variety from hybrids by saving seeds over a few seasons, selecting seeds from the plants that most resemble the cultivar you’re trying to save.

You’ll want to make sure that the fruit/flower head that you’re saving seed from is mature. This can be tricky for some vegetables, because we eat them in their immature states. Peppers need to change from green to whatever their color is (red, yellow, orange, purple, etc), cucumbers and zucchini (and other squash) need to turn into those massive, bloated fruits that often change to yellow or orange. Beans often need to change to yellow or tan (and may have stripes). For flowers, the seed heads or fruiting structures often need to turn brown and dry or start to open.

If the weather cooperates, you’ll want to collect seeds from dry fruits/structured (beans, some flowers, etc) before significant rainfall so that seeds don’t become wet and potentially mold or break dormancy. Collect seeds and place in a warm, dry location to let them continue drying out (if they’re small you want to put them somewhere they won’t blow away). After drying, store seeds in envelopes or containers and put them in a cool dry place. I often tell people to store seeds in the freezer – the cold temperature slows down respiration in the seeds and can extend their lifespan (the fridge is too moist/humid). If you do that, drop your envelopes or containers down into a sealable container or bag to help keep condensation minimal when you pull them out of the freezer next year.

For home gardeners, it may not matter that you get plants next year that exactly copy the ones you saved seeds from – the fun can be in the surprise. Who knows, you may discover a new variety – at least one that is exciting to you. It can be fun seeing the variation in your new plants and finding something that you love.

Epilogue: A special case – tomatoes

Most of the vegetable crops we grow don’t need any special treatment to break their dormancy (you’ll have to research flowers on a case-by-case basis) – save the seed and plant it next year and it will pop up. Tomatoes are a bit of a special case. If you scrape the seeds out of the fruit you’ll notice they’re still covered with the “goo” from inside the tomato which is called interlocular fluid (interlocular = between seeds). The coating persists on the seed even if you wash them. It has long been held that this coating retains some of the hormones of the fruit (like abscisic acid) that inhibits germination (though not all experts agree). So many sources will tell you to go through some process to break down the coating left on the seed, most commonly by placing the seeds and associated goo in a container, adding a bit of water, and letting them ferment for a few days. You can dump them out and wash off all the gunk. Whether or not this is required to break dormancy is up for debate, but it does provide you with clean seeds that you can store easily. There is also some evidence to suggest that this fermentation process helps remove pathogens on the exterior of the seed (heat treatment can help remove interior pathogens as well).

Some people just scoop out the seeds and smear the goo on a paper towel and try to scrape them off next year. Some people add the step of washing, but this will still not remove all of the goo coating the seeds. This works if you’re not trying to share (or sell seeds) since they will stick to the paper towel. My guess is that the in the day or so that it takes for the goo to dry there is enough fermentation or decomposition going on to break dormancy. If you don’t want the seeds stuck to a paper towel, you can use wax paper or some other non-binding surface, but you’ll still have dried goo on your seeds.

Some like it hot… but most do not: How high temperatures delay pollination and ripening

Ah, summer – vacations (pre-COVID), swimming pools (pre-COVID), ice cream, vegetable gardens, and, in many places, really high temperatures. These things all go hand-in-hand (or at least they did before the pandemic). Many gardeners feel that the heat of mid-summer goes hand in hand with garden production; those high temps driving production on those fruiting plants like tomatoes and peppers. But…..could they be wrong?

We’ve had lots of extra hot days this summer in Nebraska, so it stands to reason that we should have really great production on those garden favorites like tomatoes, right? Then tell me why our extension office has received numerous questions this year about why tomatoes aren’t setting on or ripening. Heck, we even had a Facebook post about tomatoes not ripening in the heat go viral (well, for our standards – 300,000 views/2,000 shares). Could it be a disease? Nope – it’s the heat. High daytime temperatures can have a big effect, but the effects are compounded when nighttime temperatures are high as well.

Tomatoes not ripening? You're not alone. Temperatures above 85 degrees will slow down the ripening process. Temperatures above 95 can stop the process all together. #NebExt #NeWX
Posted by Nebraska Extension in Douglas-Sarpy Counties on Wednesday, July 22, 2020

It turns out that high heat does two things in many of those fruiting vegetables (and of course fruits) that we grow. First, it inhibits pollen production, which in turns reduces fruit set. Second, heat inhibits gene expression for proteins that aid in ripening/maturation of the fruit. Heat stress also reduces photosynthesis (Sharkey, 2005) in many different plants, which would slow down plant processes (such as fruit development and ripening) as it reduces the availability of sugars to fuel these processes. So high heat can not only reduce the number of fruits developing on the plant, but also slow down the ripening process for fruits that have already set. And if you think that these effects only happen at super extreme temps, most of the research studying temperature effects of this nature use a common “high ambient temperature” of 32°C/26°C for daytime/nighttime temperatures. For us U.S. Fahrenheit-ers, that’s 89.6°F/78.8°F, which isn’t really all that hot for most of us.

Many studies show that application of this “high ambient temperature” to crops such as tomatoes, beans, and corn during the pre-fertilization phases of reproduction (ie – flower/pollen development) can negatively effect fruit set. The introduction of Porch and Jahn (2001) gives a pretty good overview of literature detailing the effect in beans (Phaseolus vulgaris). I’ll sum it up here: heat stress while the pollen is forming (called sporogenesis) led to pollen sterility and failure of pollen to release from the anthers (dehiscence). It also led to flower abscission (basically the plant aborts the flower) and reduce pollen tube formation (how the pollen nucleus gets through the stigma to the ovule for pollination) when applied during the period of pollen sac and ovary development. And application during flower opening (anthesis) resulted in pollen injury (sterility) and reproductive organ abscission. All of these effects lead to reduced fruit/seed set in beans. (Interestingly, heat stress at the ovary development phase also led to parthenocarpy – basically the pods developed, sans seeds, without fertilization).

However, we get the most calls about tomatoes (they’re the top crop for most home gardeners). Is it the same issue? Yep. Numerous studies (Sato, et al., 2000; Pressman, et al., 2002; Abdul-BAki, 1992) show the same effect in tomatoes. Pressman, et al. (2002) linked the effects on pollen to changes in carbohydrates in the anthers (reduced starch storage and carbohydrate metabolism).

Tomato pollination and how to increase it in high tunnels — Tomato floral structures

To add insult to injury, high temperatures also slow down or stop ripening of crops like tomatoes. Picton and Grierson (1988) found that 35°C (95°F) temperatures altered the gene expression in tomato fruits – inhibiting the expression of polygalacturonase, which softens cells walls, allowing the fruit to ripen. Reduced photosynthesis would also reduce the availability of sugars for fruit development and ripening.

But there’s hope, both this season and in the long term! The effect on the plants is not permanent. When temperatures drop below that “high ambient temperature” threshold pollen production, and therefore fruit set, will return to normal (as long as the plant is healthy). Sato, et al. (2000) found that pollen release and fruit set resumed within a few days after heat stressed plants were “relieved” and temperatures dropped back into the optimal range of 26-28°C/22°C (78.8-82.4°F/71.6°F). So many of those plants will become productive again (good news for my own tomatoes and beans, which had an initial flurry of production then went on vacation), especially as we head into fall. And efforts are under way to develop and test heat stress resistant cultivars.

This last point may be more important than you realized. These production problems plague many areas around he world at current climactic norms. Many fear that increasing temperatures will limit the productive capacity of many areas of the world that are already struggling. It is easy to see how the difference in just of just a few degrees can take your veggie production from prolific to paltry.

You can also try to reduce the heat a bit yourself for an immediate fix. Shade cloth can help reduce temperatures a little bit, which may make all the difference in your garden if you’re just slightly over the “high ambient temperature” threshold.

Tomatoes under shade cloth | Tomatoes under shade cloth | Flickr — Tomatoes under shade cloth | Source: flickr.com

But in the meantime, if your vegetable garden has taken a summer siesta it will get around to producing again one day. You’ll just have to take good care of the plants in the meantime. And perhaps it’s a blessing in disguise – when its that hot I don’t want to be out working in the garden much, either.

Sources

Abdul-Baki, A. A. (1992). Determination of pollen viability in tomatoes. Journal of the American Society for Horticultural Science, 117(3), 473-476.Porch, T.G. and Jahn, M. (2001), Effects of high‐temperature stress on microsporogenesis in heat‐sensitive and heat‐tolerant genotypes of Phaseolus vulgaris . Plant, Cell & Environment, 24: 723-731. doi:10.1046/j.1365-3040.2001.00716.x
Pressman, E., Peet, M. M., & Pharr, D. M. (2002). The effect of heat stress on tomato pollen characteristics is associated with changes in carbohydrate concentration in the developing anthers. Annals of Botany, 90(5), 631-636.
Sato, S., Peet, M. M., & Thomas, J. F. (2000). Physiological factors limit fruit set of tomato (Lycopersicon esculentum Mill.) under chronic, mild heat stress. Plant, Cell & Environment, 23(7), 719-726.
Sharkey, T. D. (2005). Effects of moderate heat stress on photosynthesis: importance of thylakoid reactions, rubisco deactivation, reactive oxygen species, and thermotolerance provided by isoprene. Plant, Cell & Environment, 28(3), 269-277.