The summer is progressing, along with vegetable crops being harvested and sold at all levels of the supply chain. Even though growers are very busy, it is time to think about direct seeding or starting transplanting for those autumn vegetable crops or cool season crops that will keep the cash flowing into the winter months. I used to tell growers at winter meetings that with the advent of high tunnels we could keep them growing 13 months a year. In the same breath I’d also tell them that they needed to take a break and unwind from the hectic growing season just completed.
Cool season vegetables are for planting and growing in late winter, early spring or in late summer, autumn and early winter. These crops do best in temperatures between about 40º and 70º F. Many can withstand colder temps, but warmer temperatures can be detrimental to them. It’s important to ensure that cool season vegetables planted in spring have enough time to reach maturity before the weather turns warm and their quality deteriorates. Conversely, make sure cool weather crops planted in late summer and early autumn have enough time to reach harvest in the field before the first heavy freeze or big snowstorm. With the use of high tunnels one can go into a somewhat protected environment which can allow longer harvest of these crops, using additional protections such as row covers and thermal blankets inside the tunnels.
Growers can check their seed catalog, seed sales rep or Extension personnel if they’re unsure how many days the seed or plant requires to reach maturity. Those that have grown fall vegetables or cool season vegetables before will know by experience the length of time required for maturity. Plan your sowing, transplanting and harvesting accordingly and make sure to mark it on your calendar as a reminder so it doesn’t sneak up on you.
Hardiness is a term used to describe a cool season plant’s ability to survive winter without protection. The terms “hardy” and “semi-hardy” are important when deciding which crops to plant. Hardy vegetables can tolerate a hard frost (about 25º to 28º). The hardiest crops are kale, spinach and collards, which can tolerate temperatures in the low 20s and high teens. Other crops include broccoli, Brussels sprouts, cabbage, kohlrabi, mustard greens and turnips.
Semi-hardy vegetables can tolerate a light frost (usually about 29º to 32º). They’re good for spring and autumn but can go into a high tunnel for additional protection. Crops include beets, carrots, cauliflower, Chinese cabbage, lettuce, rutabaga, salsify and Swiss chard.
Transplants may work best for planting in autumn – that way you’re not pushed to remove your summer crops, which can remain in the field for a few weeks longer. Cool season vegetable transplants started in a greenhouse or purchased in early spring can extend the growing season as well. I like transplants, as they give me productive plants ready to grow. In the coldest growing regions, a double cover over both a high tunnel and cold frame may keep the soil from freezing.
Let’s review some crops for autumn production. I believe the quality and variety of fall vegetables has certainly improved over the years.
Arugula – an easy salad choice which matures in less than 50 days. Arugula is mild-flavored when grown in cool conditions; plant by mid-autumn in a frame or tunnel for harvest throughout winter; plant again in January.
Beets – look for varieties that mature in 55 days or less. Beets are usually seeded 10 weeks in advance of the first frost and can go into the high tunnel.
Broccoli is a good spring and fall crop. There are many varieties of broccoli now so check with the recommendations for your region.
Brussels sprouts – select varieties that mature in 100 days or less. Long-season cool weather Brussels sprouts are always best started from transplants. This is a crop whose taste improves with each fall frost. They can go six to nine weeks past freeze if given protection. A trick is to break the growing point to enhance the developing sprouts.
Cabbage is the workhorse of fall vegetables (and is both a spring and fall crop). Harvest before the first freeze.
Carrots – try to choose varieties that mature in less than 60 days. Carrots can be stored in the ground where the soil does not freeze. Grow in a cold frame protected from a hard freeze. In severe winter areas, cover carrots with straw inside the frame or grow in a high tunnel.
Cauliflower – choose varieties that mature in less than 60 days. It’s best started 10 weeks before the first fall frost. I’ve always found this crop is best grown in autumn.
Kale’s inside leaves are generally tastier than its outer leaves. Kale can be harvested from under the snow. Low-growing varieties are best for cold frames; taller varieties are not as cold hardy. Kale is an excellent candidate for high tunnel production.
Kohlrabi – this crop is best grown in autumn and winter. Grow kohlrabi outdoors until a hard freeze then harvest and store. You can grow in cold frames or high tunnels for a longer harvest. There are beautiful red and green varieties. Kohlrabi is one crop breeders have improved tremendously – new varieties can grow larger and still be edible.
Lettuce season is spring, summer and fall in colder regions of the country, and fall, winter and spring in warm regions. Choose varieties that mature in 60 days or less. Lettuce can take only so much freezing and thawing, even in a cold frame or high tunnel. It’s important that plants reach harvestable size by early winter; winter varieties can survive through winter in a cold frame or high tunnel if protected from multiple freezes. Choose leafy varieties rather than heading varieties for the earliest harvest.
Mustard greens – you can sow mustard greens in autumn for harvest throughout winter.
Parsnips are the hardiest of root crops. Plant parsnips in early summer for next spring harvest, maturing in about 120 days. They can overwinter with no protection, even in coldest regions. Dig up parsnips when the soil has thawed. Parsnips can store for four to six months. It is what I like to call one of my survival crops.
Spinach will germinate and grow at temps just slightly above freezing and continue growing until freezing. It’s a great crop for high tunnels and winter markets.
Swiss chard – choose varieties that mature in 60 days or less. Pick leaves as they mature, and the plant will continue to produce more. It will keep producing until hard frost; frozen chard leaves will come back with a thaw. Grown in a high tunnel, it can produce throughout winter.
Turnips are another of my favorite survival crops. They are the best tasting when young and tender. This is another crop with some excellent newer varieties.
As you can see, autumn (and even into winter) months can be an active time of year with a wide variety of nutritious vegetables to sell to the consuming public.
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