Zone 13 is the hottest USDA zone and the only one that is frost-free year-round, with average winter lows above 60°F. There is no last spring frost and no first autumn frost to plan around, so in Zone 13 you plant by heat and by the wet and dry seasons, not by frost. The limits on what grows are heat, humidity, rain and pests rather than cold. All numbers below are published ranges, not promises for your garden: check your local extension service before you plant.
Kohlrabi is the odd one out in the brassica family: a swollen stem that grows above ground, tasting like a mild cross between a turnip and a cabbage stem. It is a cool-season crop that matures in about seven to eight weeks, which makes it a good fit for Zone 13's short mild window. The trick is harvesting at the right size — left too long, the bulb turns woody and no amount of cooking will save it.
Zone 13 timing for kohlrabi
The table below is the whole plan in one place.
| Step | Zone 13 timing |
|---|---|
| Average winter low | Above 60°F |
| Last spring frost | None — frost-free year-round |
| First autumn frost | None — frost-free year-round |
| Best planting window | Coolest months only, roughly November to February |
| Start indoors | Optional head start indoors a few weeks before transplanting |
| Direct sow outdoors | Sow direct the coolest months, roughly November to February, or transplant seedlings |
| Days to germination | 7–10 days |
| Days to maturity | 50–60 days |
| Cold tolerance | frost-tolerant |
When to sow kohlrabi in Zone 13
Sow kohlrabi in the coolest months, roughly November to February, so the swollen stems form while the weather is mild. Start seed indoors a few weeks before transplanting, or direct-sow into a prepared bed. Sow in batches a few weeks apart for a staggered harvest, and stop sowing well before heat builds. Use the seed-starting calculator to work backwards from your transplant date.
Starting kohlrabi: indoors or direct sowing
Kohlrabi can be started indoors or direct-sown. Starting indoors gives the most reliable results in Zone 13, because you control moisture while seedlings are small and transplant sturdy plants at the right moment. Sow seed thinly, transplant when seedlings have a few true leaves, and set them at the same depth they were growing — planting too deep encourages a woody stem.
Soil, spacing and sun
Kohlrabi needs full sun. Space plants 6–9 inches apart — crowded plants compete for light, water and air, and disease spreads faster between touching leaves in humid tropical air. Kohlrabi wants rich, well-drained soil with compost worked in, and full sun in the cool season. It feeds moderately, so a compost-rich bed is enough without heavy fertiliser. Keep the soil evenly moist: dry spells make the swollen stem tough and woody, which is the most common disappointment with this crop. Use the plant spacing calculator to work out how many plants fit in your bed at that spacing.
Watering kohlrabi in Zone 13
Water needs are moderate, but even moisture is the key to a tender bulb. Water deeply at the base, mulch to hold moisture, and do not let the bed dry out completely — a kohlrabi that dries out and then gets soaked often splits or turns woody. Morning watering is best.
Companion plants
Good companions for kohlrabi include marigolds, basil, onions, lettuce. These are the companions listed for this crop in standard horticultural references: they share similar needs, and some, like marigolds, are traditionally planted to help confuse or deter pests. Plant companions in the same bed or nearby, not in a separate corner of the garden, so they actually share the space. Avoid planting heavy feeders that will compete for the same nutrients in the same spot.
Common pests and problems
The pests to watch for are cabbage worms, aphids, flea beetles and slugs. Flea beetles chew tiny holes in young leaves, and cabbage worms hide on leaf undersides, so check plants weekly and hand-pick pests. Row cover over young plants keeps butterflies from laying eggs and is the simplest protection.
Harvest and storage
Harvest kohlrabi when the swollen stem is about the size of a tennis ball, roughly seven to eight weeks after sowing — do not wait for it to grow bigger, because size brings woodiness, not flavour. Cut at the base, peel the tough skin, and eat the crisp flesh raw or cooked. Use within a few days, or store in a cool place for a week or two.
Succession and rotation in Zone 13
Succession sowing works in Zone 13, but only inside the cool season: sow a small batch every two to three weeks while the weather stays mild, so the harvest stretches out instead of arriving all at once. Once heat builds, stop sowing — a late batch will bolt before it is worth picking. Rotate crops so kohlrabi does not follow another Brassicaceae family crop in the same bed next season. Keep notes on what you sowed and when: in a climate with no frost dates, your own records are the most useful planting guide you will have for the next cool season.
Related Zone 13 guides
More Zone 13 guides: Rutabaga in Zone 13 and the same crop in a cooler zone, Kohlrabi in Zone 11. The January in Zone 13 guide shows what else to plant in that month, and the planting calendar hub brings all the Zone 13 guides together.
Frequently asked questions
When should I plant kohlrabi in Zone 13?
Sow kohlrabi in the coolest months, roughly November to February. Zone 13 is frost-free with winter lows above 60°F, so there is no last or first frost date to work from — plant by the cool season, not by frost. Check your local extension service for the best sowing weeks in your area.
When is kohlrabi ready to pick?
When the swollen stem is about tennis-ball size, usually seven to eight weeks after sowing. Pick it then, even if it looks small — a kohlrabi left to grow large turns woody and fibrous, and no cooking will make it tender again.
Can I eat kohlrabi leaves?
Yes — the young leaves are edible and good cooked like other greens. Pick a few outer leaves while the bulb is forming, but do not strip the plant, because the leaves feed the bulb you are waiting for.
What soil and spacing do kohlrabi need?
It needs full sun, soil pH 6.0–7.5, and spacing of 6–9 inches between plants. Work compost into the bed before planting and test the soil rather than guessing the pH.