Kohlrabi Growing Calendar: Spring and Autumn Crops

Decide which crop you are growing

There are two sensible slots for kohlrabi and they behave differently enough that you should decide which one you are in before you sow. A spring crop goes in as the soil warms and is harvested before real heat arrives. An autumn crop is sown in late summer heat and matures as the weather cools.

The autumn crop is easier and gives better texture, because cool weather slows the swelling and the flesh stays fine grained. The spring crop is faster but carries both risks: a cold spell can make it bolt, and a hot spell can make it woody. Most gardeners who struggle with kohlrabi are trying to grow it in spring and sowing too early.

Kohlrabi tolerates light frost once the bulb has formed and its flavor improves after one, so an autumn crop can be left a little longer than you would expect.

The autumn crop, stage by stage

Count back ten to twelve weeks from your first expected frost to fix the sowing date, then work forward. The one thing that goes wrong with autumn kohlrabi is sowing too late: the plants run out of warm weather before the bulb sizes up and sit there small all winter.

The spring crop, stage by stage

The spring crop is the same sequence compressed, with two extra jobs at the start: raising plants under cover so they are not sitting outside during the cold, and hardening them off before they go out. Everything after planting runs faster because the days are lengthening and warming.

Do not plant out a spring crop that has a stem thicker than a pencil. That is the plant that reads a cold week as a winter and bolts instead of swelling.

What to look at, stage by stage

The calendar tells you roughly when. What actually decides your crop is a short check every few days, and at each stage there is one thing worth looking at more than the others.

1. At emergence, look at the seed leaves Pinprick holes mean flea beetle and you have a few days to react. This is the only check in the whole season where a delay of a week can cost you the entire sowing.
2. At the second thinning, look at the stem thickness A short thick stem below the leaves is a plant that will make a bulb. A long thin neck means it was crowded, and no amount of space now will fix it.
3. During leaf growth, count the leaves Six to eight healthy leaves is what a full sized bulb needs. If pests have taken you below that, deal with them before worrying about anything else.
4. As the bulb swells, feel the shoulder From an inch (2.5 cm) across, check with a thumbnail every three days. The window between right and woody is about two weeks in cool weather and ten days in warm.
5. Before harvest, cut one open One test bulb tells you whether the rest of the bed has a week left or needs cutting now. It is the only reliable way to see fiber before you have picked everything.

Succession and what to grow it with

Because it only occupies ground for two to three months and stays small, kohlrabi is one of the easiest crops to slot into gaps. It fits before a late planted summer crop, or after early potatoes or broad beans have come out.

Sow a short row every two to three weeks rather than one large block. A whole bed maturing together mostly goes woody, because the good window is only a fortnight wide. Three staggered sowings of eight plants each feed a household far better than one sowing of twenty four.

1. Keep it out of ground that grew brassicas Cabbage, kale, swede, turnip, radish and mustard are all the same family. Leave three years between them on the same ground to keep club root out.
2. Follow a legume where you can Ground that has just grown peas or beans has the nitrogen kohlrabi wants for its leaf growth, and it usually comes free at the right time of year.
3. Use it as a catch crop between slower plants It matures before a late brassica or a squash has spread, so a row between them is harvested and gone before it competes for light.
4. Stagger the sowings, not the spacing Resist sowing everything at once and thinning over a long period. Sowing on three dates gives you three harvest windows and much less waste.

Write down each sowing date and the date you cut the first bulb from it. After one season you will know exactly how many days your garden takes, which is the number that makes succession sowing work.

Decisions that pay off next year

Kohlrabi is a crop where a few noted dates remove most of the guesswork the second time round. It is fast enough that the same conditions repeat closely from year to year, so last season's record is a good predictor.

The single most useful figure is the gap between sowing and first harvest in your own garden. Packet figures are averages, and yours will often differ by two weeks in either direction.