Extending the vegetable garden season with row covers, tunnels, and more

Even though the temperature may be quickly dropping, and the fall colors illuminate the mountains, and even as chrysanthemums pop up on front porches and in gardens, there’s still plenty of life left in the vegetable garden. To keep your garden growing into the fall and winter, just remember to always use protection.

Using season extension techniques it can be possible to add a few more weeks to the life of warm-season crops like tomatoes and peppers and a few more months to the life of cool-season crops like leafy greens and Cole crops.

There are several technologies available for home gardeners to protect their plants. Each technique offers a different level of protection and requires varying levels of labor and investment.

Gardeners can select the method that meets their needs and fits their budget.

Floating row cover is the easiest method to extend the life of your garden when autumn chill and winter cold threaten to put an end to your produce. This method uses a light, spun fabric that to me resembles large pieces of dryer fabric softener sheets.

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Floating row cover protecting a raised bed. Source

As the name suggests, the material simply floats on top of the plants, since it is lightweight enough to do so. These are available in a variety of weights that can add from 2 to 8 degrees of protection. This means that if a freeze at 32°F will kill your plant, you could keep it alive to as far down as 24°F. The lightest row cover can be used for insect protection during the winter, too.

The row cover material can also be placed on hoop supports to add stability and offer protection from moderate snow loads. These hoops can be made from heavy gauge wire, flexible PVC conduit, or can be bent from metal conduit using a special bender.

Bending metal conduit to form low tunnel hoops.

Since the material is spun, it is permeable to water and will allow rain and melting snow to water the plants.

Low tunnels use support hoops to support a plastic cover to form a mini greenhouse structure over the plants. The plastic is stretched over the hoops then buried or weighted down on the sides and ends. This plastic will give several more degrees of protection to the plants and can keep things warm and growing well through the winter. However, these structures have to be monitored to make sure that they do not heat up too much on sunny days and bake your crop. Since the plastic isn’t permeable, you’ll also need to keep an eye on the soil moisture. You may have to end up watering your crop in the winter if things stay warm.

High tunnels, sometimes called hoop houses, are structures that are made of a variety of materials. This is basically an unheated plastic greenhouse where the temperature is maintained through passive solar heating and venting. High tunnels are tall enough to walk through, and typically have doors, vents, and other structures built in.  Since they do not have electrical hook-ups and can be easily disassembled if needed, they are generally considered temporary structures.  This can be an important detail for permitting purposes in urban settings and may also have tax and insurance implications (greenhouses are considered by many to be more permanent and are thus taxable in most places).  Greenhouses aren’t typically used for season extension, but for propagating plants during the late winter or keeping non-hardy and tropical plants alive through the winter.

Small high tunnels would be for a very serious home gardener, as they are mainly used by farmers to push seasons late and get an early start on crops in the late winter, but for those serious about producing their own food a high tunnel may be a good option.

A high tunnel looks like a greenouse, but is typically not heated or lighted.

High tunnels are not just for vegetable gardens — you can grow a variety of fruits in them, too. I visited a Pueblo village in New Mexico that was feeding their families with dwarf fruit trees in high tunnels since the desert got too cold at night to produce apples.

The heat in high tunnels can be a chore to manage, as the temperatures can warm up quickly. The sides need to be raised and lowered in the spring and fall when temperatures fluctuate to avoid freezing or frying the plants inside. High tunnels will also require that the crops be watered. Using drip irrigation or another irrigation method is almost a necessity with this growing system.

Cold frames are smaller structures that usually have a glass or plexi-glass cover. This is an excellent way to recycle old windows or glass doors in the garden. They can be well-built with lumber, or could even simply be bales of straw arranged in a rectangle with an opening in the middle covered by a window.

The most effective designs have the glass angled to get the most of the available winter sunlight. These structures can heat up pretty quickly, so you’ll have to watch and crack the lid if things heat up too much. Cold frames are great for getting an early start on cool season crops, or even starting transplants like tomatoes and peppers.

Using season extension can greatly increase the lifespan of your garden. Even something as simple as floating row cover can help keep your produce coming for weeks if not months beyond the first frost.

For more information on season extension, I found a great website by my colleagues at the University of Maine Cooperative Extension (if anyone knows winter, it should be them). You can find it at http://umaine.edu/publications/2752e/

John Porter
Urban Agriculture Program Coordinator at Nebraska Extension

John Porter is the Urban Ag Program Coordinator for Nebraska Extension and Nebraska College of Technical Agriculture, serving both as an extension educator and professor of urban agriculture. He specializes in urban agriculture and horticulture, especially in the areas of vegetable and fruit production for home gardens and urban farms and edible landscaping.


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