When to Harvest Kohlrabi Before It Turns Woody

Tennis ball size, and not much bigger

The whole of kohlrabi harvesting comes down to one number: about two and a half to three inches (6 to 8 cm) across. That is a tennis ball. At that size the flesh is crisp, sweet and cuts like an apple. It is the size at which the crop is worth growing.

Past about four inches (10 cm) the core starts to lignify. Fibers run through it, the texture goes from crisp to stringy, and the skin thickens into something you have to peel deeply rather than pare. The flavor goes hot and coarse at the same time. This happens over a fortnight, not overnight, but it is one way traffic.

Autumn crops grown into cool weather hold their quality longer than spring crops, because everything is slower. A spring crop in warm weather can go from perfect to woody in ten days, so check it every few days once it is past two inches (5 cm).

Days from sowing are a rough guide only. A cold fortnight can push everything back by two weeks, so always confirm by looking at and feeling the bulb.

How to tell a good one from a woody one

You can judge kohlrabi standing over it, without cutting anything, if you know what to look at. All three signs point the same way, and when two of them agree you can trust the answer.

1. Press the shoulder with a thumbnail A ready bulb gives slightly and the nail marks the skin easily. A bulb that resists a thumbnail has a thickened skin, and thickened skin means the core has started to go fibrous.
2. Look for cracks radiating from the leaf scars Fine cracks around where the leaf stalks join mean the bulb has grown faster than its skin, usually after rain following a dry spell. Cracked bulbs will not store, so use them first.
3. Cut one across the middle Cut a test bulb in half. Uniform pale flesh with no visible fiber running through it is right. Visible strings, a slightly translucent core, or a woody ring under the skin means the rest of the bed needs picking now.
4. Check the leaves When the lower leaves start yellowing off and the newest leaves at the center are much smaller than the rest, the plant has finished swelling. Nothing is gained by leaving it.

If the test bulb is already woody, harvest the whole bed the same week and use the biggest ones cooked. There is no stage after this where they improve.

Cutting and trimming

Do not pull kohlrabi. The roots come up with a mass of soil and the flesh gets bruised where you grip it. Cut it, and cut it in the right place.

1. Cut the stem below the bulb Slide a sharp knife under the bulb and cut through the stem about half an inch (1 cm) below it, leaving the roots in the ground. Lift the roots separately afterwards with a fork.
2. Take the leaves off straight away Cut the leaf stalks about an inch (2.5 cm) from the bulb. Leaves left on pull moisture out of the bulb and it goes soft and rubbery within two days.
3. Keep the young leaves The inner leaves are worth cooking. Separate them from the coarse outer ones in the garden and take them in the same day.
4. Do not wash it Brush the soil off dry. A washed bulb goes moldy at the cut surfaces far faster, so wash only what you are about to eat.

Harvest in the morning while the plant is full of water. A bulb cut in the afternoon heat is already slightly limp before it reaches the kitchen.

What you lose by leaving it too long

There is no reward for growing a large kohlrabi. Unlike a swede or a cabbage, the extra size is all fiber. A six inch (15 cm) bulb is not four times the food of a three inch (8 cm) one, it is a woody object with a shell of usable flesh around the outside.

Leaving them also blocks the ground for the next crop and, on a spring sowing, gives the plants time to bolt as the weather warms. A bolted plant sends up a flower stalk from the center of the bulb and the flesh around it goes stringy within days.

If a batch has run away from you, grate the usable outer flesh rather than trying to dice it. Grating cuts across the fibers and salvages bulbs that are otherwise unpleasant.

Storing what you cannot eat now

Kohlrabi keeps far better than most people expect, provided the leaves come off and it stays cool and slightly humid. Trimmed and bagged it holds in a fridge for weeks, which makes it a genuinely useful crop to harvest all at once when a bed is ready together.

What it will not tolerate is being left in the ground in warm weather as a store. Unlike a winter root crop, the ground is not a good store for kohlrabi once the bulb is mature, because it keeps growing and going woody.

Store the leaves separately and use them within two or three days. They wilt long before the bulb does, and left in the same bag they push moisture into it.