Plant Palette

Plant Palette

Extending the Growing Season

Photo of Jennifer Schultz Nelson

Jennifer Schultz Nelson
Extension Educator, Horticulture
jaschult@illinois.edu

The 90 degree weather may have lulled us into a false sense of never-ending gardening, but Fall weather is finally upon us. As the temperature drops, many gardeners look for ways to keep their garden going just a little longer.

If you are a vegetable gardener, it is possible to harvest some crops well into the winter months. Root crops like carrots, beets, and turnips can be left in the ground well after the first frost. A heavy layer of mulch or straw will prevent the ground from freezing and allow these crops to be easily dug even during the winter. Many people have noted that these crops actually taste a bit sweeter after having been exposed to frosty temperatures.

Other crops that tend to taste better after experiencing a frost are the brassicas–broccoli, cauliflower, cabbage, and Brussels sprouts. For a fall crop of these vegetables, these plants should have been set out in late July or early August at the latest.

Not every fall crop needs to have been planted in midsummer. Fall is a great time to enjoy other cool weather crops like spinach, lettuce and radishes. These plants don't need much more than about 45 days to produce an edible crop, and survive light frost.

With a little added protection, these fall vegetable harvests can keep producing into the early winter, maybe longer depending on the outdoor temperature.

Accomplishing this feat requires that you find a way to capture the heat energy produced by the sun during the day. While sunny Fall days are comfortable and even somewhat warm, longer nights contribute a lot to a loss of heat energy from the soil. Shorter days means less time to recoup this energy, and over time the soil cools to a temperature even cool season crops cannot tolerate.

One way to combat this cooling is to use a floating row cover or hoop house. Both methods involve covering the crop and capturing the heat of the sun, creating a microclimate around the plants that is a few degrees higher than the surrounding air. A floating row cover may or may not have inner supports to hold the covering above the plants, but is usually designed to be accessed by opening up or flipping back the cover. Hoop houses tend to be much larger, rigid arcs supporting a plastic cover, almost like temporary greenhouses. Some may be big enough to stand up in.

Another method typically used in conjunction with row covers or hoop houses is a layer of black plastic over the soil. The black plastic heats up and traps the heat of the sun during the day, radiating it to the plants at night. This method can be used to speed warming of the soil in the Spring as well.

Cold frames are another method to enclose a small garden space and capture heat from the sun. They are like mini-greenhouses. A simple one consists of a wooden frame topped with a rigid plastic or glass roof hinged on one side for easy access and ventilation.

But what about bringing the garden indoors? I have heard accounts of people growing crops like lettuce indoors, using supplemental lighting. Lettuce is one of those crops that can tolerate lower light than most vegetables. Success with lettuce doesn't depend on the plants flowering and fruiting like most other plants grown in the vegetable garden.

If you dream of growing vine-ripened tomatoes indoors, you should plan on building a heated greenhouse with high powered supplemental lighting. While you can successfully start tomato seedlings in your spare bedroom or basement under fluorescent lights, growing them to maturity complete with fruit requires a lot more heat and light than most people can provide in their home.

While indoor vegetable gardening may be limited, there are a lot more plants from the flower garden that may be brought indoors successfully. Many plants from the outdoor annual garden can successfully survive and even thrive indoors. I've had spectacular successes and failures at trying this myself. I would never try and overwinter all of my annuals–I just don't have the room! But I think it's at least worth a try in bringing the unique or special ones indoors.

When bringing annuals indoors, decide whether just want them to survive until next Spring, or actually have them flower and grow indoors. Many plants have very specific growing requirements, but there are a few general rules of thumb to keep in mind.

Most outdoor annuals will need supplemental lighting to flower indoors, even "shade loving" plants like impatiens. Shade outdoors in the summer has more light than even most sunny windows in the winter.

It is possible to provide adequate supplemental light without having to buy expensive "grow" lights and fixtures. A simple fluorescent fixture, often marketed as a "shop light" will only cost you around $10-$15. For the bulbs, use regular fluorescent lights, but use one "warm" bulb and one "cool" bulb in each fixture. Together the wavelengths of light from these different colored bulbs give spectrum adequate for plant growth.

Add in an inexpensive timer to turn your lights on and off, and you're set. I set my lights to be on for 16 hours and off for 8 hours each day. Place your lights as close to your plants as possible for best growth.

I don't have the space to provide supplemental light to all my plants. For those plants that aren't under lights, I give them the most light I can near windows. Be careful to not let plants actually touch cold windows and cause damage to the plants.

In my own experience, the crucial element in plants surviving indoors for the winter is watering. Plants without supplemental light will slow down considerably, and will not need much water. Too much water will just promote root rot in these cases.

Even plants under lights will probably need less water than they do during the summer. Check the plant before you water–just stick your finger in the soil about an inch deep to see that it really is dry before watering.

Cutting back plants will stimulate growth–without enough light, this growth will be weak and straggly. Sometimes even supplemental lighting is not enough to produce good sturdy growth, so in many cases it's best to save pruning and cutting back for the Spring.

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