Fall Gardening Know How (Part I): Growing Brassicas

Posted: July 22, 2016

Brassica oleracea.

Some forms of this amazingly diverse species are prized for their large leaves, others their swollen stems or clusters of unopened flower heads. Think broccoli, Brussels sprouts, cauliflower, collards, kale, and kohlrabi. Known collectively as the brassicas, these descendants of a wild Mediterranean plant all thrive in cool temperatures. Fall is a particularly good time to grow brassicas; plants can mature as cooling daytime temperatures give way to the light frosts that make these vegetables taste sweeter. The timing of when you start seeds and transplant brassicas into your garden is critical to a successful fall harvest.

Brassica Oleracea offers a diverse range of food crops from a single parantage

We know from the writings of Pliny the Elder, that Romans adored cabbage and broccoli. Kohlrabi, derived from German words meaning “cabbage turnip” is a traditional favorite of Germans and Eastern Europeans. Brought to the Americas by European settlers, we now roast Brussels sprouts, mash steamed cauliflower, and eat kale chips. Brassicas have been finding their way to our dinner plates for thousands of years. Honor your ancestors and grow a brassica or two in your garden this fall!

When to Plant Brassicas

To determine when to start fall crops in your area, check the days to maturity for a particular crop and count backwards from your first average frost date (I find this frost date calculator handy). Since brassicas range from moderately frost tolerant (broccoli) to winter hardy (collards), the first frost will not kill your plants, meaning you can plan to harvest sometime around the first average frost date or a few weeks past, even.

For example, our first average frost date in Asheville, NC is roughly October 25th (± 11 days). Of the brassicas, Brussels sprouts have the longest time to maturity at 90 days or roughly 12 weeks. Counting ahead from today’s date, I am looking at early November as a harvest date if I were to start my seeds today. Of course you also have to factor in the time it takes for the seeds to germinate, which for Brussels sprout is between 5-15 days. So, late July-early August is a great time to start Brussels sprout seeds. Other brassicas, such as kale, have shorter maturation times (50 days) and can be started from seed in September and still produce a great fall harvest.

Broccoli Romenesco - fall planted brassicas

Soil temperature plays a critical role in seed germination. For cool season plants, such as the brassicas, seeds will germinate best when soil temperatures are 50-85˚F. Hot temperatures during early development can also negatively affect flavor or even trigger plants to bolt (i.e. flower) and die. Given that July/August daytime temperatures are still reaching into the low 90’s, starting brassica seeds indoors is a great way to avoid the heat. Transplants will be ready to move into the garden in roughly six weeks or when they have 3-4 true leaves.

If you are cramped for space, tuck transplants between summer crops like corn and tomatoes—plants that may still be producing, but will soon be finished and can be cut off at the ground, making way for your brassica babies to fill in the space. If you lack the conditions that make indoor growing feasible, you can still have success this time of year by direct sowing brassicas into a shadier spot of the garden. Sow the seeds 1-2″ deeper than you wo
uld in spring and keep the area moist to moderate soil temperatures. Collard greens are good candidates for direct sowing now, as they are one of the most heat-tolerant of the brassicas.

Brassica Planting Cheat Sheet

Vegetable Days to Germination Days to Maturity Frost Tolerance
Broccoli 5-17 60-90 Moderately tolerant
Brussels Sprout 5-17 90 Very tolerant
Cabbage 5-17 70 Moderately tolerant
Cauliflower 5-15 70 Moderately tolerant
Collards 5-17 60 Very tolerant
Kale 3-12 50 Very tolerant
Kohlrabi 5-17 55-65 Very tolerant

Fall Gardening Challenges

Cabbage Worms create fall gardening challenges for brassicas

Photo Credit: Chris Smith

The downside to planting for a fall harvest is trying to establish young seedlings when pests are numerous, their populations having built up over summer. The most common pest on brassicas is the cabbage worm. Cabbage worm is a term used to collectively refer to the destructive larvae of four different species of Lepidoptera (butterflies and moths).

The white, flying adults lay their eggs on the underside of brassica leaves where the larvae hatch and begin feeding. Cabbage worms chew holes in leaves, but damage is most evident when they eat the outer margins of leaves, leaving behind a translucent edge. Inspect the underside of leaves often for yellowish eggs and the worms themselves, which are difficult to see given their color blends perfectly with that of the brassica foliage.

Excluding pests with row covers is the most effective and environmentally friendly means of preventing damage. If unable to cover plants, cabbage worms can be hand removed or treated with an organic insecticide spray such as Bt (Bacillus thuringiensis) or spinosad (Saccharopolyspora spinosa). Once your brassicas are past the young tender phase, plants can withstand some pest damage and a killing frost is right around the corner to eliminate most garden pests.
Kohlrabi is a fall harvest brassica

Written by Renee Fortner, Sow True Seed’s Agricultural Manager


References

Rupp, Rebecca. 2011. How Carrots Won The Trojan War. Storey Publishing.

Brassicas. https://plantpathology.ces.ncsu.edu/pp-vegetables/pp-vegetables-brassicas/

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2 responses to “Fall Gardening Know How (Part I): Growing Brassicas”

  1. Bill says:

    Great helpful info here. Thanks!

  2. […] Harvesting! That’s most of what we do in July. But we also tend to bugs and blights, and start the fall garden. […]

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