Broccoli

Start seed indoors 6-7 weeks before you plant out

Sow seed a quarter to a half inch deep, 6 to 7 weeks before your intended planting-out date - and that date is 2 to 3 weeks before your average last frost, not after it. Aim to produce a plant with 4 to 6 mature leaves and a well-developed root system at set-out. Broccoli has to size its head while the weather is still cool, so the crop must already be well ahead of the heat before it ever reaches the ground. Six to seven weeks is what it takes to build a transplant big enough to grow away fast but not so old that it buttons.

Sow the fall crop by counting back from your first frost

For a fall crop, count your variety's days to maturity back from your average first fall frost and sow then; leave yourself some slack, since heads size slowly as the days shorten. Choose a longer-cycle variety of 60 to 85 days so the head forms in cooling weather. Seed can start indoors or go directly in the garden, since the soil is already warm. A fall crop matures into cooling weather, which is when broccoli makes its tightest heads, but it still has to finish before hard freezes arrive. Broccoli keeps growing through the first light frosts, so the deadline is the hard freeze, and the only portable way to hit it is to count backward from your own frost date rather than trust a calendar month.

Set plants out 2-3 weeks before last frost, at 4-6 leaves

Harden plants off, then set them 12 to 18 inches apart in rows 2 to 3 feet apart, 2 to 3 weeks before your average last frost. Choose plants with 4 to 6 mature leaves and pass over the older, larger, root-bound ones. Broccoli takes frost, so going out early buys cool weather for heading. But an over-mature or stressed transplant buttons - it throws a tiny useless head instead of growing on - and plants set closer than 12 inches make smaller heads and far fewer side shoots.

Hold water steady at 1-2 inches a week as the head fills

Give 1 to 2 inches of water per week, watering deeply and infrequently rather than lightly and often. Drip irrigation is ideal. Do not let the plant dry down and rebound while the head is sizing. A drought check as the head forms is a direct cause of buttoning - the plant reads the stress as a cue to flower early and quits growing the head, and no amount of later watering undoes it. Deep infrequent water drives roots down and buffers the plant through the next hot spell.

Split the nitrogen: four weeks out, then at quarter-sized head

Four weeks after transplanting, sidedress a half cup of 21-0-0 per 10 feet of row. Apply another quarter cup of nitrogen fertilizer once the head has reached the size of a quarter. Set phosphorus and potassium from a soil test rather than guessing. Broccoli builds nearly its whole head in one short window, and a nitrogen check during that stretch is one of the things that makes plants button or throw loose, uneven heads. Splitting the nitrogen keeps it available through head fill instead of flushing past the crop while the plant is still small.

Cabbageworms: Bt at button stage, while the larvae are small

Check both sides of the leaves weekly from planting on, and more often as the season progresses. If you find two or more medium-sized larvae per 10 leaves at the button stage, spray Bacillus thuringiensis var. kurstaki, then follow with a clean-up spray 7 to 10 days before harvest. Get thorough leaf coverage - the caterpillars have to eat it for it to work. Imported cabbageworm, cabbage looper and diamondback moth larvae move into the developing head, where no spray can reach them and no washing gets them out afterward. Bt only kills caterpillars that ingest it and is far more effective on small larvae than large ones, which is why the button stage is the moment and not a week later.

⚠ Bt kurstaki kills only caterpillars that eat it and spares the parasitoids and other natural enemies that hold these pests down, unlike broad-spectrum permethrin, beta-cyfluthrin or lambda-cyhalothrin. Utah State times the final clean-up spray 7 to 10 days before harvest - treat that as your interval before cutting.

Row cover goes on the day you transplant, edges buried

Lay lightweight floating row cover over the bed at transplanting and bury the edges so no gap remains. Leave it on until harvest - broccoli is cut in bud and needs no insect pollination. Only use it on ground that did not grow a brassica crop or brassica cover crop last year. Cabbage maggot flies lay at the base of the plant and the maggots tunnel the roots, and once they are feeding there is nothing you can spray - the cover has to be in place before the flies are flying. The same cover stops cabbage butterflies and looper moths from ever laying an egg. But cover stretched over last year's brassica ground does the opposite: it traps the maggot flies emerging from that soil in with your crop.

Cut while the beads are tight, then feed for side shoots

Cut when the head is large and compact - 6 to 12 inches across on a full-size variety - and before any flower bud opens, taking about 6 inches of stem with it. Leave the plant standing. Sidedress nitrogen after cutting to push side shoots, and keep picking those smaller heads. The head IS the flower bud cluster, so once the beads loosen and show yellow the crop is past eating quality and the plant is committing to seed. Cutting the main head releases the lower buds to grow, and nitrogen right after harvest is what turns them into a second, much longer picking.