Why celeriac belongs next to your fall brassicas – and tomatoes don't
July is when broccoli, savoy and friends move into the bed – right as the cabbage white butterfly hits peak season. One old bed partner helps; two popular myths don't.
If you want to harvest your own brassicas this fall and winter, now’s the time to plant: mid-July is a classic window for young broccoli, savoy and kale plants. But right now the second generation of cabbage white butterflies is on the wing, scouting for places to lay their eggs. One time-tested bed neighbour makes life harder for them – while two popular garden myths don’t deliver.
July: planting time for fall brassicas, flight time for the whites
Broccoli, savoy cabbage and kale go into the bed as young plants now, using late summer to build strong heads and leaves. At the same time, the cabbage white is at peak season: second-generation butterflies prefer to lay their yellowish eggs on the undersides of brassica leaves. Once the caterpillars hatch, they can strip whole leaves down to the ribs within days. If you’re planting now, plan the protection right away – ideally when choosing the spot.
Celeriac and brassicas: a proven pairing
Celeriac has been sitting in many beds since May – and right next to it is the best spot for your young brassicas. Classic companion-planting wisdom has relied on this duo for generations: the strong scent of celeriac masks the cabbage smell, making it harder for the whites to locate their host plants. In turn, brassicas are considered a good partner for celeriac. Both are heavy feeders with similar water and nutrient needs – so water and mulch generously and they won’t get in each other’s way.
In practice: plant brassicas about 50 centimetres apart and run the celeriac row right alongside. Alternating cabbage–celeriac–cabbage within the row works well too.
Myth 1: tomatoes drive away the cabbage white
This tip keeps making the rounds: plant tomatoes next to your brassicas and their strongly scented foliage will keep the butterflies away. Don’t count on it – and for bed planning, the combination is actually counterproductive. Broccoli, cauliflower, white and red cabbage, savoy and Brussels sprouts are all considered poor neighbours for tomatoes in companion planting: two heavy feeders competing for water and nutrients, with tall tomato plants shading the young brassicas on top. Any possible scent effect doesn’t make up for these drawbacks.
Myth 2: onions go with everything
Onions have a reputation as the universal bodyguard – and next to carrots they do earn it against the carrot fly. Next to brassicas, though, they don’t belong: in companion planting, onions are listed as unfavourable neighbours for practically all heading cabbages, and for white cabbage that even extends to garlic. Better partners for the brassica bed are bush beans, which still have a last sowing window open in mild regions, plus dill and – sown from August onward – spinach. One detail for meticulous planners: lettuce counts as a good cabbage neighbour but doesn’t like celeriac nearby – so in this duo bed, leave it out.
What reliably protects: the netting
As helpful as the celeriac’s scent screen is, it’s no guarantee. The most reliable protection against cabbage whites is fine-mesh insect netting laid over the row right after planting and weighted down well at the edges. Still check the undersides of the leaves regularly: the yellowish egg clusters are easy to wipe off, and any hatched caterpillars can be picked off by hand. Companion planting plus netting is the most relaxed package for a clean fall harvest.
The bed planner shows you the duo at a glance
You don’t have to memorise whether your planned spot works: in Rootivo’s bed editor, tapping a plant instantly shows green companion lines to good neighbours like celeriac – and red ones if a tomato ends up too close after all.
Im Lexikon: Knollensellerie