Starting Broccoli From Seed

Starting Broccoli From Seed

Starting broccoli from seed must be done indoors in late winter and early spring. Broccoli does not like hot weather, it tends to need to be fully established before the hot weather kicks in.

If you wait too long to plant, your plants will grow with a strong flavor and they will bolt, or grow flowers. If you don’t sow your seed indoors, you can also plant outdoors directly in your garden, 3 weeks before the last frost date.

Choosing Containers

Starting Broccoli Seeds

Chose containers that will house the broccoli from seed to transplant.

If you are reusing containers from last year, scrub the containers with a bleach solution to kill any lingering diseases, A good solution is one part bleach to nine parts water,

Preparing Soil

Starting Broccoli From Seed
  • Place enough potting soil mixture for your plantings into a 5-gallon bucket
  • Wet down soil and stir it up.

The reason to plant seeds into pre-watered soil is it will not wash away the seed.  They will stay exactly where you put them.

Starting Broccoli From Seed

Broccoli Sprout From Seed

Plant seeds about seven weeks before the last frost.

Sow seeds at a depth of about 1/2 inch deep.

Place your plants in a south-facing window or set up a grow light three inches above the seedlings. Plants need at least 14 hours of sunlight a day, along with moist soil. and an average room temperature of 70 to 75 degrees F. 

Caring For Seedlings

5-10-5 Garden Food


  • Seedings like relatively cool temperatures of 60 – 70 degrees during the day.
  • Water gently.
  •  Diluted 5-10-5 liquid fertilizer to half strength, fertilize once a week with this solution.  
  • Start to gradually thin out the seedlings.  Pick a weak seeding every couple of days, until you are left with one strong two inches tall plant growing in each container. The seedlings can be thinned by cutting the seeding at the base with a pair of nail care scissors.

Hardening Off Plants For Outdoors

A month before you wish to plant outside you will have to start hardening off the plants.  Right now, the plants are not ready to go from house to garden.  The temperature indoors is warm and comfortable.  The outdoor temperature will be cooler, the sunlight directs and the wind will be drying to the stems.  To harden off my plants this is my schedule.

Week 1

Start by waiting for a day or two between watering, don’t let the plant wilt though.  This will stunt the plant’s growth.  If you are fertilizing, now is the time to stop.

Week 2

Continue to keep by the watering schedule.  Place the plants outdoors in a sheltered cold frame, out of direct sunlight on the back deck during the day.  Bring the plants indoors at night.

Week 3

Adjust your watering schedule this week.  Only water when the soil is dry. Again, use a cold frame but allow a few hours of direct sunlight daily.  Add full sunlight toward the end of the week and open the cold frame to expose the plants to the elements.

Week 4

Water only when soil is dry.  Take the plants out of the cold frame.  This week you will work your way slowly up to direct sun exposure.

Planting Outdoors

Transplant the seedlings when they have at least two sets of true leaves for me this is around May 22nd. Space young plants 18 to 24 inches apart in rows that are 2½ to 3 feet apart. Feed the plants with low nitrogen fertilizer when planting.

Keep the plants well-watered during the growing season. Fertilize the plants again when they are 12 to 15 inches tall, and then when the buds first form.  

If you have time in the late winter or early spring, starting broccoli from seed is fairly easy. Using a good quality seed, potting soil, and following the instructions above will get you a healthy crop started before the hot weather of summer sets in.

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