Cheat Nature with Season Extension

Late winter and early spring are some of my favorite times. The air is crisp and fresh like no other time and you can almost feel life being breathed back into the earth and sky. As the days get noticeably longer and the warmth of the sun can again be felt on your skin again, around our house it’s time to tap maple trees and boil syrup, await the piercing chirps of the spring peepers, and prepare the “cheater” garden.

What’s a cheater garden, you might ask? Well, it’s my word for using season extension methods to plant out cold tolerant spring crops up to a month before they would be safe to plant without the use of such tactics. Using season extension gives gardeners a whole “cheater” season on either the front or back (or both) of the growing season.

A simple low tunnel design that can maximize your growing time.

Season extension can be easy, but it’s certainly not for the faint of heart. It takes planning and discipline, and it all starts with nursing a few of your favorite spring crops into little seedlings that will take to transplanting out in the cold. It’s easy and rewarding, and cool season leafy greens are some of my favorite garden veggies! But it needs to be done carefully and deliberately or else you’ll set back your plants for weeks, or at worst, have whole flats of frozen plants. Follow along to learn more about the methods, structures, and tactics that make for successful season extension.

What is Season Extension Anyway?

If you’re intentionally planting a spring or fall garden, the use of season extension gives you about 6 weeks extra growing time.

Put simply, season extension is the use of some sort of low cost covering or structure to cover your plants during times when temperatures are too cold for vigorous growth. This can be as simple as a plastic sheet draped over them, all the way to a full greenhouse. If you’re intentionally planting a spring or fall garden, the use of season extension gives you about 6 weeks of extra growing time. In my location in the Midwest, I can plant cold hardy seedlings out as early as late March. That means by May 1 – a full two weeks away from my average last frost date – I’ll already be harvesting some spinach, lettuce, collard greens, and other varieties! Without the use of a season extending cover or structure, I wouldn’t be able to plant outside until the middle to end of April. That means I can get nearly one extra full rotation in by the time my warm weather crops even need to go in the ground, maximizing my space and making the most out of my small garden.

You can then apply this to the warm season crops too, and move them outside a few weeks early under the protection of your season extender. This is a little more risky – because warm season crops are very susceptible to cold you have to watch for freezes – but can work effectively for getting a jump on these crops too.

How Does Season Extension Work?

During the cool temperatures of late winter and early spring, the ground is frigid. While some plants can tolerate cold, and their seeds will even germinate as low as 45F, they just won’t grow very fast at those temperatures, and not at all below them. Season extension acts just like a greenhouse, even if it’s just a sheet draped over the soil. The sun still shines in March, and begins to grow ever more intense as spring draws near. That heat energy is trapped under the sheet or structure, and warms the soil. Sometimes, this warming is quite dramatic. I’ve had days of outdoor temperatures in the 20s while the ground in my low tunnels is over 60. Those are perfect soil temperatures for the roots of cold tolerant plants. In fact, I’d bet the best leafy greens you’ll ever have are those grown using season extension techniques.

I’d bet the best leafy greens you’ll ever have are those grown using season extension techniques.

Season Extension Options

There are a handful of options to try your luck with season extension. I’ll quickly go over the most popular.

Plastic Sheet or Row Cover

The easiest and most cost effective way to try your hand at the cheater seasons is with a plastic sheet or row cover material. Both of these are inexpensive, light weight, easy to use, and can perform many functions around the home and garden. To use them, you just simply drape them over your plants loosely and weight them down so they don’t blow away. Plastic sheeting is more effective for warming, but on warm, sunny days you may have to remove the covering or else risk scorching your plants. I know it’s crazy to think you could heat scorch a plant in March, but trust me, it can happen.

Row cover is a little easier to use since it’s porous, but it also doesn’t quite keep the soil as warm as a solid plastic sheet. Still, I can personally attest that I was able to start some direct sow broccoli a full 5 days earlier under row cover versus bare soil, and the difference only increases as the plant grows. You can’t go wrong with either material.

Low Tunnels

Low tunnels deployed over commercially grown strawberries. Low tunnels are a cheap and easy way to add season extension for both home and commercial gardens.

My personal favorite method for season extension is the use of low tunnels. Low tunnels are distinct from high tunnels in that they’re just inexpensive metal hoops that sit low to the ground, about 3′ tall. They’re a great option if you want the benefits of season extension, but not the burden of heating and cooling a greenhouse.

I used to have a greenhouse in the high tunnel style. I could easily walk around inside, and there was plenty of room, but it was always in the same fixed location. Personally, I eventually found the greenhouse to be less than ideal unless I wanted to cool and/or heat it, which worked against my personal garden goals. In my basement under lights worked better for starting seeds (and the heat was “free”), and by the time transplants were established it was already too hot.

Low tunnels solve those problems, and they’re very affordable too. Low tunnels are squat and infinitely portable, just 3′ tall and 2′ wide in most cases, and are versatile in many different applications. They are very easy to put together and can be moved around your garden as you see fit. When it’s cold, they can be covered in plastic sheeting to protect against cold, and the covering can be pulled back on sunny days for ventilation. When it’s hot, swap the covering for shade or insect screen and the tunnel frame becomes a 3-in-1 simple garden structure. At the end of the year they can be broken down and stored for use the following year. It’s really an incredible solution and I highly recommend you give it a try!

Caterpillar Tunnels

“Caterpillar” tunnels are the same basic concept as a low tunnel, just bigger. That requires a slightly more involved install, but is still dead simple.

Caterpillars are used a lot in market garden and small farm operations. They’re bigger than low tunnels, but just as simple. Typically they consist of a few hoops and some bracing that runs end-to-end, a few screws, and some cables. Covered in the same plastic as the low tunnels, the plastic is longer than the building and is bunched up at the front and back, where it’s staked to the ground. This provides the lateral stability to keep the building standing, and caterpillars can withstand an entire winter’s worth of snow and wind.

Caterpillar tunnels have been popularized by the likes of Eliot Coleman and others, who use them all winter for an unprecedented (and very difficult) winter garden harvest. Even if you’re not using them for this reason, they’re still a nice half-way point between a full greenhouse and the very affordable low tunnels. Use these mostly when you need a little more space to move around inside.

Season extension is a very rewarding garden practice that every serious gardener should try. It’s not the easiest, but nothing feels better in the garden than conquering the elements. What are your tricks for successful season extension? Leave us your ideas in the comments below!

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