Start your broccoli seed indoors in late winter and early spring. Broccoli does not like hot weather, it tends to need to to 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.
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 to kill any lingering diseases. A good solution is one part bleach to nine parts water.
Place enough soilless potting mixture for your plantings into a 5 gallon bucket, wet it down and stir it up. The reason I plant my seed into pre-watered soil is then I will not wash away the seed. They will stay exactly where I put them.
Poke hole on the bottom of the containers and fill each pot about an inch from the top with a soilless potting mixture which will encourage quick growing. Make a row about 1″ long and 1/2″ deep. Sow 4-5 seeds along the row. Cover the row with more of the mixture. Label the containers with the variety and the date planted.
Place the pots in a black gardening tray or an old kitchen roasting pan. If you do not have an indoor greenhouse, cover the tray with plastic wrap to retain moisture. Place the tray in a warm place. Until the seed sprout direct sunlight is not needed.
Once you see that the seed has sprouted, remove the plastic wrap and place the tray in a sunny window. Everyday make sure you give your plants a quarter turn to be sure all sides of the planting will receive sun. If you do not have a sunny window you will need to place fluorescent lights above your plants.
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 seedings can be thinned by cutting the seeding at the base with a pair of nail care scissors.
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 direct and the wind will be drying to the stems. To harden off my plants this is my schedule.
Week 1- Start by waiting a day or two between watering, don’t let the plant wilt though. This will stunt the plants 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 end of the week and open cold frame to expose the plants to the elements.
Week 4 – Water only when soil is dry. Take the plants out of cold frame. This week you will work your way slow up to direct sun exposure.