Spring cabbage, kale and purple sprouting broccoli planted out now spend the next few months as the easiest meal in the garden. Late broods of cabbage white butterflies are still laying, and once other food thins out, pigeons will strip a bed of seedlings in a morning. A hooped cover of fine insect mesh stops both without touching the plants, and it goes on in under an hour.

Net Autumn Brassicas Against Cabbage White Caterpillars and Pigeons

What you need

5 flexible garden hoops or canes bent to an arch, spaced about 90cm apart
1 roll fine insect mesh, around 1.35mm enough to cover the bed with a 60cm overlap at each end
10 ground pegs or bricks or timber battens along the edges instead
5 hoop-end caps old bottle tops work, to blunt exposed wire or cane tips

Step by step

Check the brassicas closely, top and underside of every leaf, and rub off any cabbage white eggs or caterpillars already there — the mesh will trap whatever is underneath when it goes on.
10 min
Cut the mesh to the length of the bed plus an extra 60cm at each end and 40cm at each side, so there's enough to peg down well clear of the plants.
10 min
Push the hoops into the soil at even intervals along the bed, bracing each one low and bringing it to the same height so the mesh won't rest on the leaves.
10 min
Drape the mesh over the hoops and pin or weigh down every edge — pegs in soil, bricks on a hard path — leaving no gap at ground level for a butterfly to walk through or a pigeon to push under.
10 min
Cap every exposed hoop or cane end with a bottle top or proper cap before you leave the bed.
5 min

Afterwards

Lift one edge weekly to check for anything trapped inside before the mesh went on, hoe out weeds that come up in the sheltered, moist air underneath, and re-peg any edge the wind has worked loose. Fold and store the mesh dry over summer so it doesn't rot or attract mice.

Questions

What mesh size do I actually need?

Around 1.35mm mesh keeps out cabbage root fly as well as the butterflies. Wider 5–7mm mesh only stops butterflies and pigeons, which is fine if root fly hasn't been a problem on that bed before.

Can the mesh stay on all winter?

Yes, for hardy brassicas like kale and purple sprouting broccoli — it gives a little frost protection too. Just check it isn't holding heavy snow that could collapse the hoops.

I already have bird netting up — do I need this as well?

If the gaps are wider than about 5mm, cabbage white butterflies will still get through to lay eggs, so it's worth swapping to fine insect mesh rather than doubling up.

Will covering the bed stop pollinators reaching anything?

No — brassicas grown for their leaves this season don't need pollinating, so a fully sealed cover isn't a concern here.