Why Won’t My Broccoli Form Heads? 9 Essential Tips

3. Neutral pH

Another reason your crops may fail to produce is because your soil is too acidic or too alkaline.

Close up of a broccoli plant, yet to form a head, a soft focus background of soil and other plants.

Again, a soil test is your best bet for determining pH. However, generally speaking, the addition of garden lime per package instructions helps to lower acidity, and an application of compost, leaf mulch, or peat moss helps to raise it.

Broccoli prefers a pH between 6.0 and 7.0, and may not set heads without it.

4. Adequate Spacing

The instructions on packets of seeds contain recommendations for spacing. For broccoli, it’s generally 18 inches apart with 24 inches between rows.

This ensures that each plant can send out roots to feed unimpeded by its neighbors, and that the airflow between plants is cool and low in humidity.

Three rows of broccoli seedlings, planted on soil mounds, with a channel between them.

With improper spacing, plants may exert energy fighting to survive, instead of producing heads.

Similarly, if you are growing in containers that are too small, roots may become bound, inhibiting their ability to absorb nutrients.

Remember to provide a depth of 12 to 15 inches and a width of 18, to accommodate feeding roots and mature plant dimensions.

5. Even Moisture

Another reason for failure to head is inadequate moisture. Germinating seeds and seedlings need to be kept moist and should never completely dry out.

Young plants benefit from a layer of mulch. It not only aids in moisture retention, but also inhibits water-hogging weeds.

Three broccoli seedlings with a hand on the top left of the frame with a watering can, watering the root of a seedling, prior to planting. A trowel lies on the soil, with a soft focus garden background

Once established in the garden, broccoli requires 1 to 1.5 inches of water per week. The best way to measure its intake is with a rain gauge. If it doesn’t rain, supplement with a garden hose, because fluctuating moisture levels may be detrimental to head formation.

When watering is necessary, be sure to do so in the early morning or late evening hours, and aim the hose at the soil around the base of each plant, for optimal absorption.

6. Excellent Drainage

Another issue that may result in an absence of heads is poorly draining soil. While this vegetable needs consistent moisture, it cannot thrive in standing water without becoming vulnerable to disease, pests, and rotting.

Close up of a watering can, showering water onto a freshly prepared soil mound. A soft focus background of vegetable rows, with stakes, in light sunshine.

If you find you’ve made an error in site selection, or haven’t got ideal soil, a rainy spell may leave your plants in a puddle. And plants that are stressed by oversaturation may fail to form heads.

You can try to salvage them by gently poking holes into the soil at the foliage perimeter with a dandelion weeding tool, and/or mixing leaf compost or coarse builder’s sand into the soil to improve drainage.

7. Cool Temperatures

The ideal temperature for growing broccoli is between 60° and 75°F. Temps below 30° and above 75°F may spell disaster in the form of frost and heatwaves that cause stress on developing plants, and may result in the failure to form heads.

A wooden soil thermometer, in the ground, showing a temperature of 40°F. Soil and seedlings in a soft focus background.

To manage cool temperatures for success:

  • Use your USDA hardiness zone as a guide to selecting varieties appropriate to your growing season.
  • Follow seed packet recommendations and avoid sowing seeds or transplanting indoor-grown seedlings to the garden too soon, which may expose them to temperatures that are too cold.
  • Start indoors about eight weeks before the last frost date in spring and put them outside when they have two sets of true leaves, about two weeks before the last frost date.
  • For direct-sowing, choose a variety with a short number of days to maturity, or you may find your plants succumb to summer heat before setting heads.
  • Avoid shocking seedlings started indoors by acclimating them gradually to outside temperatures. This is a process called “hardening off,” in which you set the pots of seedlings outdoors for a few hours each day for several days prior to transplanting them into the garden.
In the center of the frame is a translucent white floating grow cover, over crops. To the right is a black floating shade cover. On the right is a row of vegetables without a cover.
  • Anticipate cold snaps by having floating row covers on hand to pop over plants to keep them warm.
  • Apply several inches of mulch around plants to increase the ground temperature when especially cold weather is predicted.

To manage warm temperatures for success:

  • Use caution when sowing a late summer or early fall bumper crop, as a spike in temperatures may result in stress that causes “buttoning,” or forming multiple tiny heads, or “bolting,” a term for prematurely flowering and going to seed.
  • While buttoned or bolted broccoli is edible, in terms of quality, it falls far short of the robust heads desired.
  • Seek out heat-tolerant varieties for late summer and early fall planting. Choose varieties with a short growing season, as plants need to be well-established before cool weather sets in.

8. Time to Mature

Sometimes it appears that a broccoli plant is not heading, when in fact, it just hasn’t matured yet. Read seed packets closely, because dates to maturity may range between 50 and 100 days.

Close up of a small broccoli head with large leaves surrounding it. The mulched soil seen through the gaps in the stems.

Be sure to choose varieties suited to your USDA hardiness zone. Otherwise, your growing season may be too short for plants to have a chance to set heads before the weather turns either too hot or too cold.

And while you’re studying seed packets, don’t forget to read the plant descriptions. While most have a photo, those from a local grower may not, and you may find that you have a sprouting broccoli variety that grows multiple small florets instead of a large head.

9. Pest and Disease Control

The best ways to avoid pests and disease are to:

  • Start with quality seed or plants from a reputable company.
  • Choose a location with adequate sun, soil, and drainage.
  • Provide ample spacing.
  • Maintain even moisture.
  • Manage temperature fluctuations.
  • Keep the garden weeded and free of debris.
An unhealthy broccoli plant with holes in the wilting leaves, on a background of mulched soil.

In cool temperatures, there are fewer active pests. However, during the summer, some pests to watch for include:

And diseases you may encounter include:

To deter insects, consider floating row covers or an application of food-grade diatomaceous earth. And to address disease, choose an organic fungicide.

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