Broccoli: Sow and Grow Guide

Broccoli: Sow and Grow Guide

Broccoli heads are actually clusters of flower buds. One of the most healthful vegetables, it's packed with vitamins C and A, potassium, iron, and folic acid. Broccoli grows best in cool conditions, and in many climates, cool conditions are more consistent in fall, making broccoli a more reliable crop for fall harvest. If you were wondering how to grow broccoli from seed, you've come to the right place!


When to Sow Outside: 4 to 6 weeks before your average last frost date, or when soil temperature is at least 40°F, ideally 60°–85°F. Also, in late summer for fall harvest. Mild Climates: Best sown in fall or winter for cool-season harvest.

When to Start Inside: 4 to 6 weeks before your average last frost date. Transplant 1 to 2 weeks before your average last frost date.

How many do I plant? Each plant will produce one main head followed by small, bite-sized side shoots. How much do you love broccoli?

broccoli start


Use a lightweight seed-starting mix/medium (sterile, and lighter than potting mix), and sow seeds ⅛" deep, 3–4 seeds per pot. Thin to the strongest plant once leaves appear (clip extra plants at the soil level using scissors). The strongest plant may not be the tallest; look for thick, strong stems and deep color. By thinning early, you minimize the negative impact of crowding, like stretching for light. Read more indoor sowing tips.


Containers should be clean, sanitized, and have drainage holes. If you choose to sow in cell packs, you may need to up-pot seedlings once into larger containers before transplanting outside.


After hardening off, transplant seedlings 18″ –24″ apart (refer to the plant tag on the seed packet).


Sowing preparation and spacing

Broccoli thrives in average to rich soil. A soil test is the best way to know if your soil needs amendment. Sow 3-4 seeds 18″ –24″ apart (refer to the plant tag on the seed packet).


Once seedlings are 2" tall thin to 1 seedling every 18″– 24″.


Keep evenly moist for best production.


A soil test is the best way to know what, if any, amendments are needed. If soil is deficient, apply a slow release, balanced (equal parts nitrogen, phosphorus, and potassium) fertilizer prior to planting or a balanced, liquid fertilizer regularly once seedling have several sets of leaves.


Keep plants well weeded. Weeds compete with crops for light, nutrients, and water, and can harbor insects and diseases.

Special Care

Avoid stressing small plants. If small broccoli plants are stressed by temperatures that are too hot or too cold, heads begin to form prematurely (called "buttoning") and heads will be small. Buttoning can also happen when seedlings were kept in a growing container too long, are grown in poor soil, or are exposed to drought.

Mulch to retain more even moisture and remove any infected plants from your garden. To prevent the spread of disease, do not compost crops you suspect are infected. It is also a good idea to rotate brassica crops annually, so they are not grown in the same area for 3 years to prevent the buildup of diseases in the soil.

broccoli romanesco


Harvest when the main head gets to their optimal size (see inside the seed packets), and florets are enlarged but are still closed. Smaller, side shoots will follow and should also be harvested when florets are plump but before the stems elongate or the flowers open.


Fresh: Store in a sealed container in the produce drawer of the refrigerator for up to 2 weeks. Frozen: Blanch by dropping in boiling water for 2 minutes; then dunk in ice water, dry thoroughly, and store in freezer-safe containers.


Cabbage loopers and cabbage worms are common broccoli pests. They chew holes in the leaves, usually from the underside of the leaf. Aphids also are known to attack tender broccoli shoots and florets. Aphids can be dislodged from plants with a strong stream of water, suffocated with an organic insecticidal soap spray, or deterred with an organic neem product. Both pests can be blocked from plant by covering plants with row cover. Broccoli does not need to be pollinated, so it can remain continually covered, unless you are harvesting, to keep pests at bay. If you intend to keep plants covered for the season, keep in mind they can get 3' tall and use row cover supports that are tall enough. For more information on these and other common garden pests read our article Pests ID, Prevention, and Control.

Back to blog