The Hensley’s team trials and selects brassicas season after season. As more growers and eaters come to appreciate the range, flavor and nutrition of this crop family, also called the crucifers or cole crops, demand for new and improved varieties has climbed.
That makes a steady supply of today's standout brassicas a real opportunity for market growers. They can also be tricky: many problems appear when timing, temperature, feeding, watering, or pest and disease pressure aren't managed carefully.
If you want brassicas that are healthy, attractive and full of flavor (and profitable, if you sell them), it helps to understand these fundamentals.
Timing & Temperature with Brassicas
Timing matters enormously with brassicas, but so do temperature and temperature swings. Together they are among the strongest environmental influences on how these crops develop. More on timing follows.
Temperature largely controls when a plant shifts from the vegetative stage (growing stems and leaves, including tight leafy heads) to the reproductive stage (forming flower-bud heads, florets and flowers). Brussels sprouts, flower sprouts, cabbage, Chinese cabbage and kale are all harvested before that shift. When the change happens too soon and the plant runs to flower before it's marketable, it's called bolting.
Since you can't control field temperatures much, the key is to time plantings to suit the season. Whether you're harvesting leaves, heads or something in between, the tips below on timing and temperature will improve flavor, yield and quality.
The Case for Brassica Planting Programs
A planting program is a succession plan that uses different varieties for different parts of the season. It works because varieties respond differently to changing temperature and day length, so a sequence of varieties suited to each window usually does better than sowing one variety over and over all season.
- Planting program: Brussels sprouts
- Planting program: cauliflower
- Planting program: heading broccoli
- Planting program: mini and sprouting broccoli
Critical Development Periods in Broccoli & Cauliflower
Choosing varieties bred and suited for each seasonal window helps avoid several growth disorders.
- Ricey heads and bracts in the head. Young plants that go through hot spells or dry periods can form misshapen heads that are "ricey", pale, uneven and usually unsellable. If you'll be growing in warm weather (mid to high 80s °F), picking varieties suited to your area helps you avoid this. In our broccoli trials, for example, 'Imperial' and 'Monty' showed the best heat tolerance. In our cauliflower trials, the loose-curd 'Song TJS-65' stands up to hot spells better than standard white cauliflower. For growing cauliflower in mild, frost-free regions, see this guide from the University of California.
- Buttoning up. Buttoning means plants form small, premature heads that can't be sold. Several nights below 50°F (10°C) after transplanting can trigger it. Broccoli and cauliflower are more cold-sensitive than many of their relatives. Transplant at the right time for your area to prevent it; steady moisture and row cover also help young plants ride out cold snaps.
- Coping with up-and-down spring weather. Much of the nation's brassica crop comes from California's mild, steady climate for good reason: most current varieties were bred for those conditions and don't handle strong heat (mid to upper 80s °F) or big temperature swings. Heat and abrupt swings can leave broccoli and cauliflower with poor, unmarketable heads. Cabbage and Chinese cabbage, by contrast, cope far better with changeable weather and still head up well unless heat is extreme.
- Timing a late crop so it matures. Timing is critical for early, mid and late harvests alike. For a late harvest, planting a little early is usually safer than planting a little late. An early planting may see more late-summer heat, but since that happens before heads form in cabbage, broccoli and cauliflower, it rarely causes trouble. A late planting may not mature before cold fall weather arrives, and the crop can be lost.
- Vernalizing 'Bonarda' late-sprouting broccoli. Among the mini broccolis, only ‘Bonarda'. The other mini broccolis Hensley’s carries need no vernalization. In the types often called sprouting broccolis, several weeks at or below 50°F (10°C), but above roughly 20°F (−7°C), are what trigger heading. Put another way, these plants only make heads once they have been vernalized by that stretch of cool weather. For this use Hensley’s carries the late-sprouting variety ‘Bonarda,’, sown in late summer or early fall, overwintered and cut in early spring, especially in coastal regions with mild winters such as the Maritimes and the Mid-Atlantic.
Frost & Flavor
Many brassicas grown where they never see cold simply don't taste as sweet as those that mature in cool weather. Kale and Brussels sprouts in particular gain much better flavor after exposure to cold.
How cold is cold, when we say "cold tolerant"?
Cold tolerance and hardiness are relative rather than exact. An abrupt freeze early in fall, before plants have hardened off, can hurt them badly, while the same temperature late in fall, after gradual cooling, does much less harm. Cold injury also adds up: several freezes do far more damage than one.
Cold tolerance varies by crop and by variety. The hardiest brassicas include kale, collards, Kalettes, and Brussels sprouts, with somewhat less hardiness in cabbage, broccoli, and cauliflower.
Are Summer Brassicas Worth Your While?
Given how sensitive brassicas are to temperature, are summer plantings worth trying?
Nobody can forecast the season, but following a planting program and recording your results helps keep supply steadier across the year.
Because so much is out of our control, our brassica planting programs are designed to work with the seasons, matching varieties to the windows where they're expected to perform best. The aim is flexible options that widen your harvest window and raise yield.
Varieties described as heat tolerant do reasonably well in most areas unless heat and humidity are extreme. Beyond those listed in the planting programs, several other brassicas are known to do well in summer.
- Cabbage. Cabbage handles heat better than most brassicas, though it still does best in cool weather. Even so, Hensley’s carries several varieties that hold up especially well in summer. 'Caraflex', 'Picadilly', and 'Tendersweet' do very well and are especially good eating.
- Collard Greens. Heat rarely bothers this crop unless it's extreme, as in the Southeast and Deep South. There, collards are usually transplanted from August to late September for fall, winter and early spring harvests; midsummer is generally too hot. Collards are also quite cold tolerant, and cool weather improves their flavor. They aren't a traditional northern crop, but they grow very well in the North.
- Mini Broccolis. Summer-sprouting mini broccolis are usually chosen for the traits listed in their product descriptions. 'Happy Rich' offers very good flavor and strong yields. Of the broccoli raabs, 'Spring Raab' works well for early plantings. These varieties behave much the same across the season in northern growing areas and rarely mind heat unless it gets extreme, as it does in the Southeast and Deep South. In the Deep South, plan to harvest them in very early summer from a late-winter or early-spring sowing, or plant them in fall for a winter crop.
Fertilizing Brassicas
The two-tone rosettes of 'Autumn Star' need at least 110 days from transplanting to mature.
Begin with a soil test. Brassicas are heavy feeders and need fairly high nitrogen. If your soil is already fertile, no extra feeding is needed during the season; if it isn't, side-dress with compost or a slow-release organic fertilizer. Soil test reports usually include useful rate recommendations.
Work compost or fertilizer in with a hoe, without injuring roots, so less of the nitrogen is lost.
To push head or sprout formation, or to slow growth before dormancy, stop feeding by midsummer so plants slow down and harden for fall.
Feeding in late summer keeps plants growing fast into fall, leaving them soft, lush and more prone to frost and cold injury. This matters most for crops harvested late into fall, winter or spring, such as Brussels sprouts, Kalettes (flower sprouts), cabbage and sprouting broccoli.
Irrigating Brassicas
Brassicas need steady moisture. Plant them where you can water reliably all season. About 1" of water a week is a good general target, and consistent watering produces healthier, more productive plants than letting soil dry out badly between irrigations.
Brassicas in Abundance
Growers around the world have long found clever ways to protect brassicas from temperature extremes. For ways to cope with heat, see Getting Your Cold-Loving Crops Through the Heat of Summer. For cold-season methods, see our Hensley’s Winter Growing Guide.
There are many ways to limit pest and disease damage, too. For an overview and more resources, read Common Brassica Pests & Diseases.
As more people discover what brassicas have to offer, demand for a dependable supply will keep growing. Our trials and selection work aim, year after year, to offer the best-tasting, best-performing varieties for market farmers and home gardeners. Whether this crop family is new to you or you've grown it for years, we hope our selection covers your needs through the seasons. Good planning, quality seed and sound growing practices make a brassica program well worth the effort.
