The timing of brussels sprouts can be a challenge for home gardeners. This cole crop requires a long growing period, and it needs to mature before the first serious frost. Brussels sprouts love temperatures between 60 and 70 degrees, and if it gets too hot, they turn bitter and don't firm up well.
Plant seedlings in summer about 3 months before the first frost predicted for your area. Brussels sprouts do best if they can mature in the cool fall weather. If your climate doesn't allow for that time span, substitute a heat-tolerant variety to plant in spring and harvest in summer.
Start seedlings in a protected, shaded area. Three or four weeks before transplanting them, add compost to your garden to help hold moisture. Brussels sprouts like soil that's rich in nitrogen, drains well and can stay moist. Plant the seedlings in sun or partial shade between 2 and 3 feet apart.
Water frequently to keep the soil moist, but don't overdo it with standing water. Apply a nitrogen-rich fertilizer about every 20 days. Remove 3 or 4 lower leaves each week to help the plant develop, and about 20 days before harvest, cut off the top to help the sprouts mature.
Harvest the sprouts when they're firm and between 1 and 2 inches wide. The ones at the bottom should be ready for picking first. Snap off the sprouts, or use a knife to cut them from the stem.