Cool-Season Crops and the Tools That Keep Them Growing

The arrival of autumn doesn’t have to mean an end to the homegrown harvest. In fact, I harvest a wide variety of vegetables in fall and even into winter, protecting them with season extenders like cold frames or mini hoop tunnels.

Related: Browse all of our articles from expert grower Niki Jabbour

The key to success with year-round harvesting is to pair the right plants with the right season extenders.

The right plants are cool-season vegetables like lettuce, spinach, kale, scallions, carrots and Asian greens. These are planted from midsummer until early autumn, depending on the crop. As for the right types of season extenders, I’ve got more on that below.

When selecting seeds, read the variety description carefully, looking for those that are more tolerant of cold. For example, ‘Auroch’ spinach is one of my go-to varieties for winter harvesting. The smooth, upright leaves are very cold hardy and it’s ideal for a cold frame, mini hoop tunnel or greenhouse. ‘Rouge d’Hiver’ lettuce is another excellent salad green for autumn and winter. The green-bronze leaves stand up well in cold weather.

The name of the variety is often a clue to its cold hardiness. ‘Winter Density’, ‘North Pole’, and ‘Winter Marvel’ lettuces are among my favorite varieties to grow in fall, winter and very early spring. Another example is ‘Winter King’ cabbage, a savoy-type cabbage whose flavor gets sweeter as the temperature drops.

Once you’ve picked your vegetables and varieties, read the “days to maturity” information to learn how long they take to go from seed to harvest. ‘Rouge d’Hiver’ lettuce takes about 50 days to form full-sized heads. To gauge planting time, I count backward from my last expected fall frost date, which is approximately October 20. That brings me to August 31. Because vegetables grow a bit slower as the days get shorter in autumn, I add an extra week of growing time. Therefore I would plant Rouge d’Hiver lettuce seeds on August 24.

Other vegetables I like to grow for autumn and winter harvesting include daikon radishes, Chinese cabbage, peas, beets, parsnips, cabbage, broccoli, turnips and leeks.

Related: “What to Plant in the Vegetable Garden in Autumn”

There are many types of season extenders you can use in your vegetable garden. Most I make myself, but you can also buy structures like mini tunnels and cold frames from garden-supply stores. Here are four types of season extenders to use in the fall and winter garden:

A mini hoop tunnel is simply a small greenhouse with two main components: hoops and a cover. I use materials like half-inch-diameter lengths of PVC conduit or 9-gauge wire to make hoops. I space these two to three feet apart and then cover the space with sheets of row cover or clear poly, keeping it securely attached with snap clamps or by weighing down the sides. Lightweight wire hoops are fine for fall vegetables, but I replace them with stronger PVC hoops before winter and the snowy weather arrive.

Mini hoop tunnels are ideal for spring, autumn and winter harvesting, particularly for tall crops like mature kale plants, leeks, broccoli, spinach and scallions. Depending on the crop and cover material, a mini tunnel can extend the harvest by weeks or months.

Related: “Cold Frames and Hoop Tunnels Need Fall Maintenance”

Cold frames are handy structures and compact enough to fit in even the smallest garden spaces. A cold frame is a bottomless box with a clear top. The box protects vegetables from damaging winds and weather, and the top captures solar energy to raise the interior temperature.

I make cold frames from durable wood like hemlock or cedar and top them with a sheet of polycarbonate or an old window. Garden stores also sell cold-frame kits. These typically have polycarbonate boxes and tops, and they aren’t as insulating as frames with a wooden box. Whatever type of cold frame you build or buy, you’ll want to place it in a spot where it receives full sun through winter. Most cold frames have slanted tops to maximize the light that enters the structure; the slant should face toward the south.

Having a protected walk-in structure like a polytunnel or greenhouse is a game changer in the garden. They provide more growing space than a cold frame or mini hoop tunnel and can be used in a variety of ways. My polytunnel is perfect for starting seedlings in spring, wintering over tender crops like artichokes, growing heat-loving vegetables in summer and providing me with leafy greens and root crops in fall winter and early spring.

As with other types of season extenders, you can DIY or buy a greenhouse or polytunnel, with many sizes and styles available. Because I live in a coastal area where hurricanes and heavy snow are annual issues, strength and durability were important to me. I looked at a lot of structures and eventually bought a 14-by-24-foot polytunnel kit. It offers plenty of growing space, has sturdy steel hoops to hold up in extreme weather and the sides roll up for easy ventilation. Plus, it fit my budget. Polytunnels, also called hoop houses, cost much less per square foot than a glass or polycarbonate greenhouse.

Lastly, don’t underestimate the magic of mulch! Among the most basic season extenders, a thick layer of straw or shredded leaves provides an insulating winter blanket for root and stem crops like leeks, carrots, beets and parsnips.

In late autumn, before the ground freezes, apply a 10- to 12-inch-thick layer of mulch atop garden beds. Cover the mulch with an old row cover or bedsheet to prevent the lightweight materials from blowing away in windy weather. Whenever you want to harvest, just lift the fabric and reach under the mulch to pull a few roots. Quick and easy!

Related: “Fall Is the Time to Attend to Soil Health”