Kohlrabi is the odd one out in the brassica family: a swollen stem that tastes like a mild cross between cabbage and broccoli, crisp and sweet when young. In Zone 12 it is a reasonable cool-season choice — faster and more heat-tolerant than most brassicas, though it still prefers the mildest months. This guide tells you exactly how to grow it: when to sow, how to start seed, what soil and spacing kohlrabi needs, how to water it, which neighbours help, which pests to watch, and when to harvest. Zone 12 is frost-free, with average winter lows of 50 to 60°F, so there is no last or first frost date to plan around — here you plant by heat and by the wet and dry seasons, not by frost. See the full planting calendar for the whole year, and check your local extension service for advice specific to your area.
Kohlrabi at a glance in Zone 12
All figures below are broad published ranges from standard horticultural references, not exact figures for any variety or garden — they vary by variety, climate and soil. Use them to compare crops and to plan, not as promises.
| Detail | Kohlrabi |
|---|---|
| Days to germinate | 7–10 |
| Days to maturity | 50–60 |
| Spacing (inches) | 6–9 |
| Soil pH | 6.0–7.5 |
| Sun | full sun |
| Sowing method | both |
| Cold tolerance | frost-tolerant |
| Water needs | moderate |
When to plant kohlrabi in Zone 12
Sow kohlrabi at the start of the coolest months, roughly December in most Zone 12 areas, so it has the longest possible mild run. The published maturity range is 50–60 days, which fits the cool season well, and you can sow small batches every few weeks for a continuous supply. Kohlrabi is more heat-tolerant than cabbage or broccoli, but hot weather still makes the stems woody and quick to bolt, so the coolest months are the safest bet. Because the zone is frost-free, with winter lows of 50 to 60°F, there is no frost date to count from — sow by temperature, and check your local extension service for advice specific to your area. Our December in Zone 12 guide shows what else to sow that month.
Starting kohlrabi
Start kohlrabi indoors or sow directly: germination takes 7–10 days and seedlings are quick and vigorous. Sow in individual pots or modules, or direct in the bed, and thin to the strongest plants. Space plants 6–9 inches apart — they need room for the stems to swell, but not as much as a cabbage. Transplant carefully and water in well, or sow direct and thin once seedlings are a few inches tall. The plant spacing calculator helps you work out how many plants fit your bed. Kohlrabi is forgiving of a rough start, which makes it a good first brassica.
Soil, spacing and sun
Kohlrabi needs rich, well-drained soil with a soil pH of 6.0–7.5. Dig in well-rotted compost before planting, since kohlrabi is a hungry feeder for its size. Good drainage matters in tropical wet seasons, so a raised bed is the safest choice. Full sun suits kohlrabi in the cool season, but in Zone 12 a spot with afternoon shade helps during hot spells and keeps the stems tender. Mulch thickly to hold moisture and keep the soil cool. Feed lightly through the season with compost or a balanced liquid feed.
Watering and feeding
Kohlrabi needs moderate, steady water. Keep the soil evenly moist from planting to harvest — dry spells make the stems woody, tough and quick to bolt. Water at the base in the morning, and mulch thickly to slow evaporation in tropical sun. In the dry season, a deep soak once or twice a week is better than daily sprinkles. Avoid wetting the leaves late in the day, since damp foliage in humid air invites disease. Consistent moisture is the key to crisp, sweet kohlrabi; uneven watering produces woody stems.
Companion planting
Good companions for kohlrabi are marigolds, basil, onions and lettuce. Onions are useful neighbours that may help confuse cabbage pests. Lettuce can fill the gaps between young plants and shades the soil. Marigolds at the bed edges may help with soil pests. Avoid planting kohlrabi next to other brassicas in the same season, since they share pests, and do not follow any brassica with another brassica in the same bed — rotate to a different family next season. For another root brassica from the same season, see our guide to Rutabaga in Zone 12.
Pests and problems
Watch for cabbage worms, aphids, flea beetles and slugs. Cabbage worms are the main threat: the small white butterflies lay eggs on the leaves and the green caterpillars chew holes. Cover plants with fine insect mesh from planting, and check the undersides of leaves weekly, picking off caterpillars by hand. Aphids cluster on tender growth and can be washed off with water. Flea beetles pepper young leaves with small holes — mesh helps here too. Slugs hide in the damp shade at the base; check at night and remove them by hand.
Harvest and storage
Harvest kohlrabi when the stems are about the size of a tennis ball, usually within the published maturity range of 50–60 days from sowing. Do not wait for bigger stems — oversized kohlrabi turns woody and tough. Cut the stem at the base, trim the leaves, and peel the tough outer skin before eating. Eat fresh the same day for the best flavour, or store in the fridge for a week or two. Kohlrabi is excellent raw in salads and slaws, roasted, or in soups and stews. The young leaves are also edible when cooked.
Frequently asked questions
Is kohlrabi good for Zone 12?
Yes — it is one of the better brassicas for Zone 12. It matures in just 50–60 days and copes with warmth better than cabbage or broccoli. Sow in the coolest months.
When do I pick kohlrabi?
When the stems are about the size of a tennis ball — usually 50–60 days from sowing. Do not wait for bigger stems, or they turn woody and tough.
Why is my kohlrabi woody?
Usually heat or drought. Kohlrabi turns woody in hot, dry weather. Water steadily, mulch thickly, give afternoon shade, and harvest as soon as stems are tennis-ball sized.
Can I eat kohlrabi leaves?
Yes — the young leaves are edible when cooked, like other brassica greens. The stem is the main crop, but do not throw the leaves away.