How to Grow Broccoli
For a spring crop, look to sow seeds indoors, in a greenhouse, in a polytunnel, or in a cold-frame two or three weeks ahead of the last expected frost date.
For an autumn or early winter crop, look to sow seed 85 days before the expected or typical date of a first frost.
Planted to a depth of 1-2 centimeters, seeds can be sown in planting compost in single plugs, or 5-10 centimeters apart in a seedling tray.
Sowing the Seeds
Ideally, broccoli should not be planted in the same place in which another Brassica crop was grown the previous year. Rotating patterns of cultivation breaks up disease transmission from the soil, and as the nutritional demands of different crops vary, it allows for different soil nutrients to be taken up or replenished every year.
Sow seeds 1-2 cm deep. The plants need at least 50 centimeters of space between rows, in order to leaf out to their full potential.
Broccoli prefers a slightly acidic soil (6-6.8 pH), which can be achieved with the addition of organic matter like compost.
Roughly three weeks after germination, broccoli transplants should be given a fertiliser boost that prioritises soil inputs of nitrogen, calcium and potassium.
If the weather is too warm, a broccoli crop will “bolt,” producing a narrow stalk of flowers that blooms quickly. Since it is the unopened flower buds that are eaten as a vegetable, broccoli crops should be kept cool. In unseasonably-warm weather, use a shade cloth to protect Brassica plants like broccoli from the heat of the sun.
Mulching around the plants with decomposing organic matter like straw or wood chips will help suppress competitor plants, and will also keep the soil below cool and moist. In times or situations without rainfall, a broccoli crop should be roughly watered once a week.
Mulching around each plant with coffee grounds or eggshells, in addition to providing soil nutrition, can help keep slugs at bay.
An old gardener’s trick to deter the cabbage moth caterpillar–the bane of Brassica growers everywhere–is “companion-planting” rows or broccoli with marigolds (Tagetes spp.). Though evidence is anecdotal, their strong scent reportedly confuses adult butterflies looking to lay their eggs.
Another method is in using a “trap crop”: nasturtiums (Tropaeolum spp.) are closely-related to broccoli, and (again, anecdotally), cabbage moths with preferentially lay their eggs on the leaves of these edible blossoms, instead of a vegetable crop.
Alternatively, broccoli can simply be grown under a row cover, which keeps many pests out entirely.
When the heads have reached a diameter of 12-15 centimeters (60-90 days after planting), it is time to clip them and harvest them. Side-shoots can be continually harvested for some time after the main head is clipped.
Recommended Broccoli Varieties
- Calabrese Broccoli: A popular variety from Italy. Produces delicious 5″ broccoli heads. After main heads are harvested the plants continue to produce plenty of side shoots.
- De Cicco Broccoli: Another delicious variety from Italy. Produces tasty 3-4″ broccoli heads. Plants grow from 20-30″ tall. After harvesting the main heads, plenty of side shoots will grow throughout the summer.
- Broccoli Rabe: Also know as broccoli raab or rapini. It is a cruciferous vegetable that is very popular in Italy and China. The flavour is nutty and bitter; it goes well with meat and seafood. It’s a highly nutritious plant. The stalks, leaves, and buds are all edible.