Brassicas are one of the most versatile vegetable families in the organic garden — different varieties can be grown in succession throughout the whole season. 🥦
Main varieties and seasons
| Plant | Transplant | Harvest |
|---|---|---|
| Early cabbage | March–April | June–July |
| Autumn/winter cabbage | May–June | September–November |
| Broccoli | March–April | June–September |
| Kohlrabi | March–August | 50-70 days |
Care
- Start seedlings 4-6 weeks before transplanting
- Spacing: cabbage 50-60 cm, broccoli 40-50 cm, kohlrabi 20-25 cm
- Water evenly — heavy watering after drought splits the head
Organic pest control
Cabbage white butterfly (Pieris brassicae)
- Remove yellow egg clusters from the underside of leaves by hand
- Green caterpillars → Bacillus thuringiensis var. kurstaki (Btk)
- 0.8 mm insect netting (prevention)
Cabbage root fly (Delia radicum)
- Insect netting protects seedlings at planting
- A paper collar around the stem prevents egg-laying
Harvest and storage
- Broccoli: harvest while the flower buds are tight and green
- Cabbage: store at 0-2°C, humid air — keeps for months
🔗 Related articles
Summary
Brassicas: insect netting against the butterfly, Btk against caterpillars, 4-year crop rotation. Storage varieties give fresh vegetables even in winter! 🥦
- Why does it take insect netting as fine as 0.8 mm to stop cabbage white butterfly and cabbage root fly — wouldn’t a wider mesh work?
The female cabbage root fly lays rice-grain-sized eggs, only 1-2 mm across, right on the soil surface at the base of the stem, so the mesh needs to be fine enough that the adult fly can’t get through at all to reach the plant. A 0.8 mm weave still lets in enough light and air for photosynthesis, but physically blocks both the butterfly and the fly from accessing the plant right through to harvest.
- Why does Bacillus thuringiensis var. kurstaki (Btk) work specifically against cabbage white caterpillars, and why is it safe for other insects?
Btk is a soil bacterium that produces specific crystal proteins which activate and paralyse the digestive system only in caterpillars (Lepidoptera larvae) — in the digestive systems of other insect groups, such as bees or ground beetles, this protein simply has no effect. Because the active substance only works after ingestion, in the caterpillar’s gut, spraying needs to be timed to the young larval stage, when they’re actively feeding on the leaf.
- Why does a paper collar around the stem help against cabbage root fly if the fly approaches by flying?
The female cabbage root fly specifically seeks out the damp, shaded spot right where the soil meets the stem to lay her eggs, since the hatching larvae need to be able to burrow straight into the root. The paper collar physically blocks this critical laying site, so even though the fly can move freely above the plant, it can’t place its eggs where the larvae could reach the root.
- Why does heavy watering after drought split the head, and why isn’t overwatering itself the real cause?
During drought, the outer leaves of the head keep growing slowly and toughen up, while the growth of the inner leaves slows down — when abundant water then reaches the roots, the inner leaves suddenly swell, but the now-stiffer outer leaf layer can’t keep up with this sudden increase in volume and splits. Even, regular watering prevents precisely this sudden mismatch between inner and outer growth, rather than the total amount of water being the issue.