Broccoli is a cool season crop that prefers full sun, but will tolerate some shade. It needs well-draining soil with a pH between 6.0 and 7.0. To increase the fertility of your soil before planting, mix in up to four inches of mature compost. If your soil is in particularly poor condition, add additional high-nitrogen fertilizer to enrich the soil. Organic fertilizers like alfalfa, cottonseed meal, and aged manure are good choices when planting broccoli.
For a spring or early summer harvest, start your broccoli indoors 6-8 weeks before your last frost date, and transplant the seedlings into the garden about 3 weeks before the last frost. Your transplants should ideally be about 4” tall when they go in the garden. For a fall harvest, find the days to maturity for the variety you’re growing, and then plant seeds that many days before your area’s first frost date. If you use floating row cover, you can cheat your planting date later by several weeks. In some climates, it’s possible to direct seed fall broccoli crops outdoors, but in hotter climates such as the Southeast, it’s often too hot out for cool season plants to thrive when fall seeding time rolls around. Starting your fall broccoli seeds under shade cloth or indoors in the AC may be best.
When transplanting, space your plants 12-24” apart in rows 36” apart. Apply an organic mulch made of mature compost, leaves, or bark to keep weeds in check and soil temperature regulated. Broccoli plants have very shallow roots. If you disturb the soil, you may accidentally break roots and damage your broccoli plants. If weeds develop around the plants, suffocate them with mulch instead of plucking them from the ground to avoid disturbing the roots.
Allow your plants between one and one and a half inches of water per week. Broccoli likes moist (but well-drained) soil. Make sure not to get the budding broccoli crowns wet when watering. Doing so causes them to mold. In particularly hot or dry conditions, increase the amount of water you give your plants. Fertilize your plants about three weeks to one month after transplanting. Fish emulsion works well for fertilizing broccoli plants.
You want to harvest your broccoli crowns when the buds are tightly closed and dark green. Avoid waiting until the buds begin to flower into light green or yellow flowers. Cut the crown where it meets the stem using garden shears. Avoid breaking the crown off. A clean cut will better encourage new growth. With a healthy cut, the broccoli plant should grow more shoots from the sides of the stem.
Broccoli (Brassica oleracea) is an insect-pollinated biennial that needs only very mild winter conditions to trigger flowering. To collect pure seed, isolate your broccoli by ½ mile from any other B. oleracea varieties that may be in flower at the same time. Collect seed from at least six different plants to ensure good vigor and genetic diversity. A common seed saving method among home gardeners is to harvest the main heads from the plants, then allow the side shoots to flower and go to seed. Pick seed pods off the plants as they turn brown and completely dry. You can open them and empty out the seeds by hand, or crush the pods all together and then winnow by pouring the seeds and chaff from one container to another in front of a fan. Make sure the seeds are completely dried before storing them in an airtight container in a dark and cool location.