Cold Crops

by: Aidan Feeney

Autumn is a time to enjoy the bounty of crops you planted in the summer, and to put the garden to bed for the winter. It is a time, for most small growers, for daydreaming and planning for next spring.

Your growing season, however, does not need to come to a complete stop. With some foresight, it is entirely possible to continue growing and harvesting crops into the winter and to over-winter crops for an early-spring harvest.

When growing winter crops, fall should be thought of as a reverse spring. On this side of the calendar, days get shorter and temperatures get cooler with each passing week. As a consequence, we have to plant cold-hardy crops and we need to sow them with precise timing so they will be mature by the time daylight hours are too short for plant growth.

Timing your fall planting

This island’s maritime climate keeps temperatures mild late into the fall and early winter. Cold-hardy plants such as kale and spinach thrive in these conditions. Because of our northern latitude, however, plants will stop growing regardless of cold-tolerance as the days get shorter.

The key to planting on the proper schedule is to recognize when day length drops to 10 hours of light. At this point, plant growth essentially shuts down. Eliot Coleman, an early pioneer in unheated winter vegetable production, refers to this time as the “Persephone period.” On Nantucket, we enter this period about a week into November.

Working backward from Nov. 10, we can calculate sowing and transplanting dates for individual crops, based on how long it takes for them to reach a harvestable size. For spinach, the crop should be seeded directly into your garden beds by mid-September for fullsized spinach and a week into October for a baby-leaf harvest.

For salad greens like arugula, mizuna and kale, seeds should be sown directly into your garden beds in the second half of September. For a winter harvest of mature kale, seeds should be planted in trays the first half of August and transplanted into your garden within the first half of September.

You can always buy plants from local growers and just transplant them if you don't want to go through the trouble of starting from seed.

Plant hardiness

Many crops commonly grown in the summer actually prefer cool weather. As a result, their eating quality is much better when harvested late in the fall and winter. You will probably notice your kale, spinach and carrots get much sweeter after exposure to cold temperatures. It is speculated that these crops produce more sugars and store them in their cells to act as an anti-freeze to help them grow this time of the year.

When growing cold-hardy crops out in the open, entirely unprotected from the elements, it is normally cold wind and direct contact with ice that damages them, rather than cold temperatures alone. With this in mind, if you are growing out in the open, find an area sheltered from the wind with good sunlight. Also, consider mulching the soil with hay, straw, eel grass or leaves to help insulate it.

The most rugged and cold-tolerant crops to grow are kale and spinach. If planted on the right dates and in a sheltered area, these crops will have no problem surviving a Nantucket winter. Crops like cilantro, arugula, mizuna and cress will carry on late into the season, but they are less likely to over-winter and remain high in quality.

Finally, crops like lettuce, Swiss chard, scallions, carrots and radishes love the cold weather, but once temperatures drop into the 20s they either die, or in the case of carrots and radishes, their roots will split and crack. One common approach to overwintering carrots outdoors is to mulch them heavily with straw and roll a row cover on top. Once temperatures drop, this added insulation will keep the soil warm and extend the harvest late into the winter.


When planting crops in the fall for a winter harvest, it is important to not over-fertilize the soil. The fertilizer will make the plant grow faster, but this actually compromises the plant’s hardiness to cold. Added nitrogen will cause the cell walls within the plant to stretch, making it more vulnerable to frost damage. Because of this, if you choose to use fertilizer, use it very sparingly.

Regular watering is always critical when establishing a crop, whether it is directly seeded or transplanted into the garden. Once the plant is established and rooted, chances are you will not have to water your crop at all. Late in the fall and in the winter, soils stay wet and in general we experience more rainy weather. For this reason, you are safe to pack away the hose for the winter and let the plants find their own water in the soil.

Protected growing

You would be amazed what a single layer of glass or plastic will provide in the way of added protection for your winter crops. It is entirely within the reach of most of us to construct either an old-style cold frame or a simple hoop structure to overwinter produce in our gardens. These structures shelter your crops from the wind and elements, and their glass or plastic coverings let in sunlight to warm the soil.

The easiest and cheapest of these structures to build is a low tunnel. Low tunnels are typically built using half-inch metal EMT pipe. Using a jig, the pipes can easily be bent into Quonset-style arches by hand. Place these arches over your garden beds and drape over them either an insulating row cover or UV-resistant clear plastic. Secure the cover with sandbags or some type of weight, and you have just constructed a miniature greenhouse.

Cold frames are typically built out of wood with a hinged glass lid on top. These work best if the glass portion of the cold frame is facing south. When building a cold frame, it is important to think about ventilation, as it is easy to overheat your plants. This can be accomplished by building vents on the top, or making it so the glass lid can be propped open easily.

These simple growing structures will also help you get an early start in the spring. They are easy to build and a fun and interesting way to experiment with growing techniques.

As summer comes to an end and we approach the darkest hours of the year, I encourage growers to not go gently into the night. With the proper planning, you will be able to have a bountiful and satisfying winter harvest. ///

Aidan Feeney grew up on Nantucket, attending Sterling College in Vermont’s Northeast Kingdom to study farming, and farmed in the Hudson Valley and on Long Island before moving back to the island this spring. He is the owner of Fog Town Farm and sells his produce weekly at Sustainable Nantucket’s Farmers & Artisans Market.

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