Arbor

How to Grow Broccoli: Spacing, Feeding, Harvest

Updated August 2026

Set broccoli transplants 16 to 24 inches apart, with 24 to 36 inches between rows, in soil with a pH of 6.0 to 6.5, and expect a cuttable central head 55 to 65 days after transplanting. Keep the soil evenly moist, feed it as a nitrogen-hungry crop, and time the crop so heads finish before sustained heat arrives. Get those four things right and the rest of the guide is detail.

How it works

Broccoli forms its head fastest in a fairly narrow temperature band. Head development is best between 54°F and 68°F, and growth slows once temperatures drop below 41°F, so both a hard cold snap and a hot stretch push the crop off its ideal pace. Among cole crops, broccoli is a comparatively heavy nitrogen feeder, which is why its fertility schedule runs richer than that of most brassicas grown in the same bed.

The most common broccoli disappointment, a small head that forms too early, isn’t a disease. It’s called buttoning, and it happens whenever something checks the plant’s vegetative growth before it’s built enough leaf mass to support a full-size head. Transplant stress, drought, weed competition, insect damage, low soil fertility, or several days of cold weather below 50°F can all trigger it, and older, root-bound transplants button more readily than young, fast-growing ones. The fix isn’t a spray. It’s keeping growth uninterrupted, especially in the first few weeks after transplanting.

What to do

Start seed indoors and set out stocky, 5- to 6-week-old transplants carrying 4 to 6 true leaves about 4 weeks before your last spring frost, into a bed in full sun; for a fall crop, start seed 4 to 6 weeks before you plan to transplant into the garden. Harden them off first — see the hardening-off guide for the schedule — since transplant stress is one of the things that sets off buttoning. Avoid transplants that are already leggy or root-bound, since those tend to button.

Space plants 16 to 24 inches apart in-row, with 24 to 36 inches between rows. Wider spacing produces larger individual heads, but it also raises the risk of hollow stem, a physiological disorder that tracks with both wider spacing and higher nitrogen rates rather than with any nutrient deficiency. Boron deficiency can produce hollow stem experimentally, but the disorder in the field doesn’t consistently line up with low boron, and boron sprays aren’t a recommended fix. If you see a hollow, pithy core when you slice a stem, look at your spacing and nitrogen program before reaching for a supplement.

At transplanting, apply a starter fertilizer at the rate on its label, then side-dress 3 to 4 weeks later. One workable rate is 1/2 cup of 21-0-0 per 10 feet of row about 4 weeks after transplanting, with another 1/4 cup once the head reaches roughly quarter-size. Side-dress again with the same nitrogen fertilizer right after you cut the central head, since that push of nitrogen is what drives strong side-shoot production afterward.

Broccoli’s roots are shallow, so water deeply and evenly, aiming for 1 to 2 inches a week and working toward the top of that range once heads begin to size up; uneven moisture during head formation is one of the more reliable ways to end up with small or loose heads. If you log “broccoli heading up” as a note in Arbor, it flags the crop’s higher water need for that stage and adjusts the coming week’s watering task instead of leaving you on a flat weekly schedule.

Harvest the central head while the florets are still tight and dark, before any yellow petals show, once the head is roughly 4 to 8 inches across, depending on variety. Cut with about 5 to 6 inches of stem attached. After that cut, side shoots develop from the leaf axils lower on the stem, producing smaller heads around 1 to 3 inches across that extend the harvest for several more weeks. Broccoli is also one of the vegetables aphids commonly colonize, often clustering in the developing head where they’re easy to miss; see aphids on vegetables if you spot them.

Zone and season notes

Broccoli is a cool-season crop everywhere it’s grown, but the risk it runs varies by zone. Utah State University Extension puts the floor at about 28°F: established plants aren’t seriously damaged by short cold spells down to there, so spring crops can take a late-season frost in stride. The bigger threat to spring plantings is the other direction. Heads need to size up before sustained heat arrives, since days above 86°F with nights above 77°F can keep plants vegetative instead of heading, and high heat leaves the heads that do form loose, branchy, and bitter.

That’s why fall crops often outperform spring ones in mild-winter zones (9–11) — they mature into cooling weather instead of racing a heat wave, and in those zones side-shoot production can continue well into fall. In colder zones, that same side-shoot window gets cut short once hard freezes set in, so the harvest stretch after the central head is shorter than it would be in a milder climate, even though the plants themselves tolerate the early frosts that end the season. For broccoli’s cole-crop relatives, see growing cabbage and growing cauliflower; cauliflower runs less tolerant of that same heat-and-cold squeeze than either broccoli or cabbage.

Sources