Fall Brassicas Canada

For most home gardeners: start your own from seed indoors in late June or early July. Canadian garden centres rarely stock fall brassica transplants in late July or August — their selection is finished for the season by mid-July. Sowing your own gives you access to fall-specific varieties (Diablo Brussels sprouts, Storage No. 4 cabbage, Belstar broccoli) that nurseries don't carry. Start seeds in 10 cm pots under lights or in a partly-shaded outdoor location; transplants are ready in 4–6 weeks. The exception: bok choy and kohlrabi are usually direct-sown outdoors and skip the indoor-start step entirely.

No — this is the one rule with no exceptions. Brassicas should not follow brassicas in the same bed in the same year. Two reasons: pest larvae (cabbage worm pupae, cabbage maggot pupae) overwinter in the soil where their food source was; and clubroot disease (Plasmodiophora brassicae) builds up in soil that grows brassicas back-to-back. Rotate brassicas to a bed that grew beans, peas, lettuce, tomatoes, or any non-brassica in the spring. Brassicas can return to the original bed safely after 3–4 years of other crops.

Three common causes: started too late (the plant didn't have enough warm days to bulk up before cool weather slowed growth); insufficient nitrogen (broccoli needs steady N to push head formation; topdress with finished compost at transplant); transplant shock (broccoli is sensitive to root disturbance — transplant in cool evening hours with deep water, and don't bare-root the seedling). Bolt-resistant fall varieties (Belstar, Marathon, Calabrese) form heads more reliably than spring-bred varieties (which often don't head up properly in fall light conditions).

After at least one light frost. Brussels sprouts harvested before frost taste bitter and sulphurous — the flavour transformation only happens after cold-induced sugar conversion. Wait until your first light frost (typically late September in zone 5, mid-October in zone 6, late October in zone 7) and then start picking. Pick from the bottom of the stalk upward as the sprouts mature; lower sprouts ripen first. In zones 6+ leave the stalk in the garden through hard frost and pick all winter — the sprouts continue to mature and become even sweeter into December.

Seven brassicas dominate the Canadian fall garden: broccoli, kale, cabbage, Brussels sprouts, cauliflower, kohlrabi, and bok choy. Kale is the most forgiving and frost-tolerant — survives temperatures down to -10°C and sweetens dramatically after the first frost (Winterbor, Red Russian, and Lacinato/Dinosaur are the cold-hardiest cultivars). Brussels sprouts are the most flavour-transformed by frost — essentially inedible from summer harvest but magnificent after October frosts (Diablo, Long Island Improved, Falstaff varieties for Canada). Broccoli excels in fall because heat-induced bolting is no longer a threat (Calabrese, Belstar, Marathon for fall). Cabbage stores beautifully through winter in a root cellar or cold garage (Storage No. 4, Brunswick, Danish Ballhead). Cauliflower is the trickiest — needs steady cool weather without sharp swings (Snow Crown, Cheddar). Kohlrabi matures fast (50–55 days) and tolerates light frost. Bok choy is the fastest brassica of all (40–45 days) and ideal for the tightest fall windows.

Fall brassica timing depends on your first frost date and which brassica you're sowing. The general rule: count backwards from your first fall frost date by the crop's days to maturity PLUS a 14-day buffer for the slower autumn growth pace. For zone 3–4 (Calgary, Edmonton, Saskatoon, Winnipeg, Sudbury) — first frost mid-to-late September — start brassica transplants indoors in late June and transplant outdoors mid-to-late July. Direct-sow fast brassicas (kohlrabi, bok choy, mustard greens) by mid-July at the latest. For zone 5 (Ottawa, Montreal, Halifax) — first frost early October — start indoors early July, transplant first week of August. For zone 6 (Toronto, Hamilton, Mississauga) — first frost late October to early November — start indoors mid-July, transplant mid-August. For zone 7–8 (Vancouver, Victoria) — first frost late November/December — start indoors August, transplant September. Brussels sprouts need the longest window: 90–100 days from transplant, so back-calculate carefully — most zone 5 gardens need them in the ground by August 1.

Three factors make Canadian fall brassicas dramatically better than spring-grown ones. First, frost-sweetening: when night temperatures drop below 5°C, brassicas convert starches to sugars as a cell-protective measure — the result is sweeter, less bitter cabbage; mellower, nuttier Brussels sprouts; richer-flavoured kale; sweeter broccoli. This is the most-overlooked secret of cold-climate vegetable gardening. Second, pest pressure: cabbage worm (imported cabbageworm), flea beetle, and aphid populations collapse with the first cool nights of September. Spring brassicas constantly battle these pests; fall brassicas largely escape them. Third, no bolting: spring-sown broccoli and bok choy frequently bolt (produce flowers and become unmarketable) when summer heat arrives — fall plantings mature into cooling weather, never triggering the bolt response. Net result: fall brassicas are easier, sweeter, less pest-damaged, and more flavour-complex than spring brassicas grown by the same gardener in the same garden.

Light frost (down to -3°C) actually IMPROVES fall brassicas — kale, Brussels sprouts, cabbage, broccoli, and collards all sweeten markedly after the first one or two light frosts. Don't panic-harvest at first frost. Harvest broccoli heads and cauliflower heads before HARD frost (below -3°C) because the curds can be damaged. Kale, Brussels sprouts, and mature cabbage tolerate down to -10°C without protection — they're essentially winter-hardy and will continue producing into November or December in zones 5–6 with no protection at all. Brussels sprouts in particular should be left on the stalk in the garden through several frosts before picking — their flavour transforms completely from summer's bitter sulfur to a sweet nutty richness. The only protection most fall brassicas need is row cover (Reemay or Agribon) when forecast lows hit -5°C or colder, which gains them roughly one additional zone of cold tolerance.

Cabbage worm pressure drops sharply by September across all Canadian zones — that alone is one of the major advantages of fall brassicas over spring ones. For the early-August transplant window (when pressure is still moderate), row cover (Reemay or Agribon) draped over the bed at transplant time keeps the white cabbage butterfly from landing and laying eggs. Bt (Bacillus thuringiensis) spray is the gold standard organic control when worms appear — it kills caterpillars but is safe for everything else. Hand-picking works for small plantings — check the underside of leaves every few days; the worms are bright green and well-camouflaged but their droppings (small black 'frass' pellets) on lower leaves give them away. Companion planting with strong-smelling herbs (thyme, sage, rosemary) confuses the cabbage butterfly. By late September into October, you can largely stop monitoring — the butterflies are gone for the year.

Yes, in zones 5+ with the right varieties and protection. Overwintering brassicas survive winter as small plants and produce in early spring weeks before any spring-sown crop is ready. Best overwintering varieties: kale (Winterbor, Red Russian, Westlandse Winter) easily overwinters under row cover in zones 5+; sprouting broccoli (Purple Sprouting, Late Purple) sown in August overwinters and produces flush of mini-broccoli in March–April; overwintering cabbage (January King, Tundra) holds in the field through winter in zone 7+ for early-spring harvest. Brussels sprouts can hold on the stalk through hard frost — pick as needed all winter in zones 6+. Cover with row cover or a cold frame for reliable overwintering in zones 5–6; in zone 7–8 most overwintering brassicas survive uncovered with reliable snow cover. In zones 3–4, only the hardiest kale (Winterbor) and only in a well-mulched, well-sited bed with reliable snow cover will overwinter — most Prairie gardeners restart in spring.

All three are the same species (Brassica oleracea) but bred for different traits. Kale: loose-leafed (doesn't head up), most cold-hardy of the three (-10°C with no protection), best flavour-transformed by frost, eaten leaf-by-leaf as a 'cut and come again' crop through fall and winter. Collards: similar to kale but with smoother, broader, less-textured leaves; common in Southern US cooking but less so in Canada — same hardiness as kale. Cabbage: heads up into a tight ball, less cold-tolerant than kale (down to -5°C), grown for storage rather than continuous harvest; the head develops over 70–100 days from transplant and is cut whole. In a Canadian fall garden: plant kale for ongoing harvest from October through January (with protection in colder zones), and plant a few cabbages for storage in a root cellar (the cabbages mature in October and store fresh for 4–6 months at 0–2°C and 90% humidity).

Three brassicas are nearly foolproof for fall: kale, bok choy, and kohlrabi. Kale germinates reliably, transplants well, tolerates a wide range of conditions, sweetens after frost, and pests rarely destroy it (cabbage worms cause cosmetic damage at most). Direct sow late July or transplant early August. Bok choy matures in 40–45 days from seed — the fastest brassica — and the cool weather of September prevents the bolting that ruins spring-sown bok choy. Direct sow in early August; harvest entire plants when 15–20 cm tall. Kohlrabi (the underground swollen stem) is 50–55 days and tolerates light frost; sweeter than spring-grown. Direct sow late July or transplant early August. Harder brassicas to start with: cauliflower (sensitive to temperature swings), Brussels sprouts (long-season), broccoli (timing-sensitive for head formation). Start with kale + bok choy + kohlrabi the first fall, then add the rest as confidence grows.