Cold Hardy Plants: Grow Edible Fresh Greens Year-Round

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Photo by Walter Chandoha
Using season-extending techniques in winter and early spring can help you produce an abundance of cold-hardy plants for great salads all year.

Fresh greens of all kinds are a year-round staple in my family’s kitchen. We have learned to transform the traditional “lean time” of the coldest months into a time of abundance by growing hardy and semihardy greens adapted to each season and using season-extending techniques in winter and early spring. Try these techniques and you’ll be thrilled the first time you pick a fresh, crisp salad right from your back yard — in the middle of January.

Our most reliable cold-hardy plants are those that have had at least one season to develop extensive root systems. Regardless of your location, these “naturals” — cooking greens and salad plants that naturally overwinter — will always be your best performers. The naturals usually can survive winter on their own with no protection in our Zone 6 region in the mountains of North Carolina, and they are vigorous early producers. In colder zones, you can use the protection techniques described below and enjoy cooked greens and fresh salads prepared from a variety of tasty and nutritious greens all winter long.

You may already be familiar with many of the stalwarts of winter gardens:

  • kale (‘Winterbor’ hybrid is among the hardiest)
  • collards
  • spinach (‘Space’ and ‘Hector’ thrive even in cold climates)
  • winter-hardy lettuces (‘Tango’ and ‘Brune d’Hiver’ are excellent choices for winter gardens)
  • salad brassicas, such as tatsoi and rape

In addition, there are two other categories of cold-loving naturals:

Self-seeding annuals that will return from year to year: 

  • arugula
  • giant red mustard
  • mâche or corn salad (‘Piedmont’ and other large-leaf varieties produce the most greens per plant)
  • claytonia, aka miners lettuce (needs a little protection)

Perennial greens: 

  • radicchios (‘Red Treviso’ lends itself to cut-and-come-again harvesting)
  • many other chicories (the traditional Italian cooking green, ‘Red Rib Dandelion,’ is super productive)
  • French sorrel
  • the spinach relative ‘Good King Henry’ (aka poor man’s asparagus)

All greens are good for you, but consider growing greens that are especially nutritious. For instance, spinach, mustard and collards are especially high in folate; kale, spinach and corn salad (mâche) are good sources of iron; and Swiss chard, chicory, kale, spinach, mustard, collards and beet greens all rank off the charts for Vitamins A, C and K.

Fall Planting

From mid-August to mid-September, sow successions of the naturals every couple of weeks. The naturals are hardy enough to overwinter anywhere in the continental United States with protection. When the greens are young in the fall, simple fabric row covers that rest on the leaves will do the trick. When the plants get a little bigger and temperatures drop, you may need to add a second layer of protection with tunnels made of clear plastic suspended by hoops or wire arches and closed on both ends. If temperatures regularly drop to near zero in your area, keep some heavyweight row covers or tarps on hand to throw over the whole setup.

Plants usually won’t overheat under fabric row covers, but you’ll need to ventilate plastic covers on sunny days when temperatures are above freezing. They will need to be closed again in the early evening, but many garden supply companies offer products that make this an easy job. (If you choose to construct your own tunnels, use UV-grade plastic so it won’t degrade quickly in the sun, and if you expect heavy snows, opt for metal conduit or rebar instead of plastic pipes for the hoops.) As the temperatures climb, you’ll need to pay more attention to ventilating your tunnels. Once nighttime temperatures are consistently near 30 degrees, you can remove the plastic but keep the fabric row cover in place. Remove the fabric cover after daily low temperatures consistently are above 30 degrees.

Winter Sowing

Fall-planted seeds begin to bolt (produce seed) with the long and warming days of spring, but succession planting will ensure a steady supply of the naturals. Most years I sow these seeds during January or February, but occasionally winter’s grip holds me back until March. You also can sow some cooking greens, such as chard and beet leaves, during these mid- to late-winter plantings. For continuous harvests, sow a new round of seeds every two weeks or so. It’s best to prepare these plots during the fall and cover them with 4 to 6 inches of leaves that will insulate the soil. You also can install a plastic tunnel over the bed to keep the soil warmer.

You’ll get the best production by planting each type of green separately, but it is possible to mix them all together. Just keep a couple of plant idiosyncrasies in mind: spinach gets lost in almost any crowd; salad brassicas will overwhelm your lettuce; mustard and mizuna will quickly dominate any bed of greens; and claytonia can make even these look timid!

Come Harvest Time

Depending on weather, your location and the varieties you’ve chosen, you’ll be able to harvest some of your fall-planted greens by the end of fall. And you can keep on picking most of these right through the winter. Others will overwinter and mature as early as the first of March. But even if you don’t get any of your salad greens in the ground until mid-February, you’ll still enjoy delicious, homegrown salads by early April.

Although most of the fall-planted naturals will be bolting by mid-spring, some — particularly corn salad and claytonia — will suffer little or no loss of quality other than the inevitable decline in production. Indeed, the tender flower stalks and buds of several brassicas are a delicious treat. Arugula flowers have a sweet, mild flavor even after the flavor of the leaves has become harsh. And the stalks and buds of overwintered collard greens may even rival asparagus!

Plant salad greens for cut-and-come-again harvests by sowing seeds just a couple inches from one another. When the plants are 4 to 6 inches tall, cut the entire plant but leave about an inch of leaf stubs for regrowth. For cooking greens, just snip off the oldest leaves each time you harvest them.

Feed the Plants that Feed You

Greens are easy to grow in most soils, but will be improved by a neutral to slightly acidic soil (pH of 6.5 to 7), plus plenty of calcium (from lime or gypsum) and nitrogen. Growing nitrogen-fixing cover crops during off-seasons is a great way to enrich your soil. Try Austrian winter peas or ‘Ho Lan Dow’ snow peas (a great culinary variety available from Stokes Seeds and you’ll be able to add tender pea shoots to your salads. Harvested just as the peas begin to flower, these sweet vine tips (snipped just below the first big leaf) taste just like peas, and the texture is delightfully crunchy. Fava beans, another great cool-season cover crop, also provide succulent, edible greens.

When you turn in the cover crop, work some compost or manure in, too. If you’ve gone through the trouble of having your soil tested, now’s the time to add any necessary amendments.

For cut-and-come-again harvesting, feed newly snipped plants with a misting of fish or seaweed emulsion after each harvest. Or use side-dressings of worm castings. Be sure to keep all your greens watered well, especially once you’ve removed their protective coverings.

Pests and Diseases

Your greens won’t require any pollinating, so if big pests such as rabbits or deer are a problem in your area, just leave the row covers over your greens. Switch to super-lightweight fabric covers at the end of spring. Be aware that aphid infestations can be a threat if you leave covers on as it warms up. If aphids appear, open the covers to let in beneficial insects. If slugs plague your garden, apply a thin mulch of coffee grounds to the soil around the plants.

Disease is most likely to show up on your older plantings. Your best allies in warding it off will be maximum air circulation, as much sun as possible and rotating crops to keep problems localized. Of course, the better nourished the soil, the more disease-resistant the crop will be.