Broccoli is one of the most nutritious crops you can grow, and home-grown heads harvested tight are noticeably crisper and sweeter than anything from a store. The challenge is heat: mature broccoli loves 60 to 65 degree F days and will bolt or produce small, loose, off-flavored heads when temperatures push above 75 to 80 degrees F. The whole game is timing transplants so the crop matures in cool conditions, either in spring before heat arrives or in fall after it breaks.
When to plant broccoli
Broccoli is planted in two windows: spring and fall.
For a spring crop, start transplants indoors 5 to 7 weeks before your last spring frost. Set them out in the garden 3 to 4 weeks before your last frost date, once transplants are stocky and well-rooted. At that point the soil is workable and daytime temperatures are reliably cool, exactly what young broccoli wants. The goal is to have heads sizing up in cool spring weather, not racing against approaching heat.
For a fall crop, which is often the better one in warm-summer climates, count backward from your average first fall frost. Take your days-to-maturity (around 55 to 65 days from transplant), add 2 to 3 weeks for hardening off and establishment, and subtract from your first frost date to find your indoor sowing date. Fall transplants often produce better-quality heads because cooling temperatures improve flavor and slow growth just as heads develop.
Hardening off matters for brassicas
Broccoli transplants need gradual exposure to outdoor conditions over 7 to 10 days before going into the garden. This step is especially important for the cole crops: cabbage family plants are cold-tolerant but still susceptible to sunscald and windburn if moved outside too abruptly. Follow the hardening off guide closely. A cold frame or portable greenhouse shelter speeds the process in variable spring weather.
Soil and site
Broccoli wants full sun and fertile, well-drained soil with a pH of 6.0 to 7.0, slightly higher than the acidic end you would target for potatoes. Good soil moisture retention is important during head development.
Incorporate a generous layer of compost before planting. Broccoli is a heavy feeder and a long-season crop; a fertile starting bed pays off in larger, tighter heads. Consistent moisture throughout the season is also important, broccoli stress during head formation produces small or loose heads.
Planting
Set transplants 18 to 24 inches apart in rows 24 to 30 inches wide. The wider spacing is important for air circulation, which reduces disease pressure, and for the large leaf canopy broccoli develops before heading.
Plant at the same depth the transplant grew in its cell or pot, firm the soil around the roots, and water in well. If conditions are cold and windy at transplant time, a floating row cover draped over the bed keeps transplants warm and protected until they are established.
Watering and feeding
Aim for consistent moisture, 1 to 1.5 inches per week, especially once heads begin to form. Stress during heading produces small, loose, or prematurely opening heads. A soaker hose or drip system along the row delivers steady moisture without wetting the foliage, which reduces disease.
Side-dress with a nitrogen-forward organic fertilizer about 3 weeks after transplanting to support the heavy leaf growth broccoli produces before heading. Avoid high-nitrogen feeding once the head is forming; too much nitrogen at that stage produces leaf at the expense of the head.
Pest pressure: the brassica insects
Broccoli shares the pest challenges of all cole crops, and the caterpillar complex is the most consistent one. Three species cause nearly all the damage:
Imported cabbageworm: The velvet-green larvae of the white cabbage butterfly. They feed openly on leaves and heads and are easy to spot. Check leaf undersides for pale yellow oval eggs.
Cabbage looper: Pale green caterpillars that loop when they crawl. They tend to be harder to find because they feed more inside the head.
Cabbage worms generally: Any of the above; scout leaf surfaces and the developing head closely as it sizes up.
Flea beetles are especially damaging to young transplants, riddling leaves with tiny holes before plants are established. Row cover at transplant time prevents damage entirely. Aphids cluster on stems and leaf undersides, especially in crowded plantings; strong water sprays dislodge them.
Row cover is the single most effective defense for the full caterpillar complex AND flea beetles simultaneously. Keep it on from transplant until heads start forming (you need to remove it for sizing and harvest).
On disease: clubroot is the most serious broccoli soil-borne disease, causing misshapen, gall-covered roots. It persists in soil for years and has no cure once present; prevention is a strict 3-to-4-year rotation away from all brassicas (broccoli, cabbage, cauliflower, kale). Black rot causes yellow V-shaped lesions on leaves and is spread by water splash; wide spacing and avoiding overhead watering reduce risk. Crop rotation is the core defense against both.
Companion planting
Kale, cabbage, and other brassicas share the same pest profile and should be rotated together (not interplanted where they reinforce each other's pest habitat). Beneficial companions for broccoli include dill (which attracts parasitic wasps that prey on caterpillars), nasturtiums (trap crop for aphids), and garlic. See the companion planting guide for more details.
Harvesting broccoli and side shoots
The main head is ready when it is fully sized but the tiny individual buds are still tightly closed and dark green. Do not wait for any yellowing or loosening of buds; once the tiny flowers begin to open the head loses flavor and quality fast.
Cut the main stem 5 to 6 inches below the head with a sharp knife. After the main head is removed, most varieties produce side shoots: smaller florets that emerge from the leaf axils. These are often sweeter and more tender than the main head. Keep plants watered and fed after the main harvest and you can pick side shoots for several weeks.
Broccoli harvest to table
Harvest at tight bud
Cut the main stem when buds are dense, dark, and fully sized but none have begun to open. A few yellowing buds mean the window is closing.
Cut with 5 to 6 inches of stem
The stem is edible and keeps the head fresh longer for storage.
Refrigerate promptly
Broccoli loses sweetness and nutrients quickly at room temperature. Use within a few days or blanch and freeze.
Leave the plant for side shoots
Keep watering and light feeding; side shoots will emerge and produce for weeks.
When should I plant broccoli transplants?
For a spring crop, set transplants in the garden 3 to 4 weeks before your last spring frost, having started them indoors 5 to 7 weeks before that. For a fall crop, count backward from your first fall frost by the variety's days-to-maturity (55 to 65 days from transplant) plus 2 to 3 weeks for establishment, and that is your transplant date. Both windows depend on your local frost dates.
Why did my broccoli bolt without forming a head?
Bolting (producing a flower stalk without a proper head) usually means the plant experienced heat stress during heading. If spring temperatures rose quickly after transplanting, broccoli may have gone to flower before producing a full head. For next season, transplant a little earlier so heads size up in cooler conditions, and consider a fall crop instead, since cooling fall temperatures are generally more reliable for quality heads.
How do I keep caterpillars off my broccoli?
Floating row cover laid over plants from transplant until the heads begin to develop is the most reliable barrier against imported cabbageworm, cabbage looper, and flea beetles. Check under the cover periodically; if caterpillars do appear, hand-pick them or apply Bt (Bacillus thuringiensis), a naturally occurring bacterium that targets caterpillars but is harmless to beneficial insects, bees, and humans.
Can I grow broccoli in containers?
Yes, though you need a container at least 12 inches deep and 12 to 15 inches wide per plant. Broccoli roots deeply and the leaf canopy is large. A raised bed is generally better than a pot for broccoli; it provides more root room, retains moisture more evenly, and makes side-shoot harvesting easier.
When is broccoli ready to harvest?
Cut the main head when it is fully sized but all the individual flower buds are still tightly closed and dark green. Buds beginning to separate or show yellow mean you are at the very edge of the window. Once flowers open, the head is past its prime. After the main cut, side shoots emerge and can be harvested over several more weeks.