Closely related to broccoli, cauliflower grows best in cool weather and is easily damaged by the heat of summer. Generally planted for spring and fall harvests, this vegetable can be tricky to grow thanks to tough soil requirements and tight temperature ranges. All cauliflower plants should at least be started indoors, and you can continue to grow them indoors with the right type of container.
Because cauliflower must be harvested before the summer heat sets in, you have to start seeds indoors during winter. Sow seeds in small planting pots or seed trays at least 6 to 10 weeks before the final predicted frost date for your area. Final frost is generally in February or March, so you will begin planting in December or January. Plant in fast-draining soil mix, keep the soil consistently moist and store the seeds at or very near 45 degrees Fahrenheit to encourage the seeds to germinate. You should see small sprouts coming up from the seeds within two to three weeks of planting.
If you intend to keep cauliflower indoors, you will need to transplant the young seedlings into larger containers. Use containers that are at least 8 inches deep. The width of the container varies by the number of cauliflower plants you want to grow in a single container. Each head of cauliflower needs at least 18 inches on all sides to grow to full size. Use quick-draining potting soil and a container that features drainage holes. If you want to create your own growing container, such as from an old storage tub, you can drill 1/4-inch diameter holes along the bottom and sides (1 inch from the bottom) of the container to create your own drainage holes.
Transplant the seedlings into the container about six weeks after planting when the seedlings have at least four good, strong leaves. Plant one of the seedlings at the direct center of the container, and plant each plant at least 18 inches removed from the first and from each other. Maintain temperature around the cauliflower between 65 and 75 degrees Fahrenheit; temperature variations will slow or stunt growth. Keep the soil consistently moist. After about a month, add aged manure to the soil to feed the plant, encouraging growth. Cauliflower is ready for harvest 70 to 120 days after seeding.
Growing Indoors for Fall Harvest
If you will grow your cauliflower indoors only and control temperature, soil and watering, you can theoretically plant at any time for a harvest at any time of year. In general, a fall harvest requires planting in the summer, which does not always result in healthy plants thanks to warm weather. However, as long as you can maintain the 65 to 75 degrees Fahrenheit temperature range, plant cauliflower anytime of year for indoor growing.