The most common brassicas grown in home gardens include cabbage, cauliflower, brocolli and kale. Cool weather plants, they are usually planted indoors in late winter and moved to the garden bed in early spring. Autumn plantings are another possibility in areas with long, cool autumns or with the help of a cold frame. While specific care instruction vary between the different varieties, starting the seeds is the same for most members of the brassica family.
Prepare your outdoor beds in fall before the ground freezes for spring planting. Choose a well drained, rich garden bed. Work 2 to 3 inches of compost into the soil bed to raise it, aiding drainage and soil quality. Firm the soil after working the bed by walking on it, then cover with a straw mulch over winter, removing it before spring planting.
Start brassica seeds indoors eight weeks before the last predicted frost date in your area. Fill starter pots or trays with seed starting soil mix. Make your own by mixing one part vermiculite with one part compost.
Plant seeds in the center of pots or 6 inches apart in trays. Sow 1/2 inch under the soil surface.
Water the soil so it is evenly moist throughout. Cover in plastic wrap and place in a warm place to germinate. Germination takes seven to 14 days for most brassica varieties.
Remove the plastic wrap once sprouts appear. Place the seedlings in a warm, sunny window and water as needed to maintain moist soil.
Transplant outdoors from four weeks before the last frost date in your area to two weeks after, depending on the specific variety of brassica. Harden the plant off before transplanting by moving it outside for two hours each day, gradually increasing the time outdoors until the plants spend the entire day outside at the end of seven to 14 days.
Water the seedlings well before transplanting. Dig holes deep enough so each seedling sets at the same level in the garden bed as it did in the starter pot. Space the plants as directed on the envelope for the particular variety.
Keep the soil moist at all times. One to two deep waterings a week are sufficient. Most brassica require 1 to 2 inches of water weekly.