by Tom Zink, hortuculturalist

Gardening is a year-round sport.  With summer high temperatures winding down and the approach of fall, it’s a great time to grow cooler-season crops.  Each season brings unique garden challenges, but the end result is always rewarding.

This month’s article explores techniques to extend the season into fall and winter.  It examines crops that tend to do well in cooler temperatures and even overwintering, along with adjustments that need to be made with cooler growing seasons.  Just because the summer season is over doesn’t mean the growing has to stop!

Season extension typically means cultivating cold-season crops with the goal of extending the growing season throughout the winter.  Although information in this article may also be used to transition growing from spring into summer, the overall goal is to outline a plan for fall and winter production.

Crop and variety selection play a huge role in being able to grow into the colder seasons. Choosing appropriate cooler-season crop varieties that are resilient yields a higher chance of success. Delicate summer crops can be extended and grown in a heated greenhouse with supplemental lighting; however, it’s a costly practice.

Greenhouses and high tunnels make season extension easier, but aren’t mandatory, and one may find Agribon® row covers for field production the most cost-effective. Agribon® is rated by weight and frost protection, so intensity of winter climate will determine the amount of protection needed. A good rule of thumb is the higher the AG(Agribon®) rating, the more insulation/protection.

Agribon® ratings and specifications are as follows:

Remember! Agribon® shouldn’t be left on plants long-term, and should only be used during freezing periods. Gently drape directly over plants or low tunnel hoops. Low light transmission from its continued use can stretch plants and disrupt chlorophyll production.

Greenhouse and high tunnel cold season production can produce some of the tastiest crops of the year. These shelters add a layer of protection against frosty nights and chilly winds. An internal heat source and Agribon® may also be used inside to guard even the most sensitive crops. The goal isn’t to warm up to daytime temperatures, but to always keep the environment bumped above freezing.

Managing moisture in the tunnel is also imperative in the cold season, as excess moisture can lead to fungal and mold outbreaks. When temps outside reach above freezing, it’s recommended to ventilate and air exchange. In an enclosed greenhouse, consider using dehumidifiers, in addition to air intakes and exhaust fans, to prevent problems.

Watering plays a big role in season extension and should be used strategically during the cold time of year. Because of the slow rate of evaporation, watering can be used as a frost preventative; however, timing is key.
If a freeze is anticipated, deep watering early in the day will act as a natural frost blanket for roots of plants. Water is trapped in the soil and heated by the sun throughout the day and slowly evaporates and cools through the night, becoming a layer of insulation.

This technique is especially useful with harder frost. Do not water already frozen ground or when temperatures are below freezing! This will greatly damage plants and could lead to crop loss.

Selecting the most appropriate crops for the season is the number one key to success in the garden. Some crops benefit from growing in colder temperatures.

A freeze on certain crops (leafy greens, root crops, and brassicas) converts starch to sugar, making for a noticeably sweeter taste while also extending out their harvest window. This extra sugar acts as a biological shield protecting the plant when temperatures drop below freezing.

Greens like lettuce, kale, chard and spinach thrive in the cooler season and can be grown down to the high 20’s with little protection. Root crops also do great, especially if established before the cold hits.

Crops like carrots, beets, turnips, and radishes can be harvested throughout the winter with higher sugar content and better flavor, while crops like onions and garlic can be overwintered for spring production and harvest.

Brassicas, like cabbage, broccoli, and brussels sprouts, are also cold hardy and need just a little protection in freezing temperatures. Be aware: growth rates do slow as the temperatures drop, and it’s best to go into the extreme cold season with these plants already established.

Winter doesn’t mean the end of the garden, it just means an adjustment. With the help of strategic watering, Agribon® coverage, low/high tunnel use and proper crop selection, you can continue producing healthy, tasty crops throughout the colder seasons.

The best thing about winter production is the lack of weeding and pest pressure. For some, this is when the season really starts!