Insect Netting for Brassicas Without the Common Mistakes

Two summers ago I lost 140 feet of fall broccoli to cabbage worms in about nine days. The plants looked fine on a Monday, and by the following Wednesday half the leaves were lace. The next year I covered the same bed with insect netting the day I transplanted, and I picked every head. I did not spray once.

Insect netting is the cheapest crop protection most small farms are not using properly. It is a fine mesh laid over hoops that stops moths, flea beetles and root maggot flies from reaching the plants in the first place. Done well, it replaces most of the spraying on brassicas. Done badly, it becomes a warm tent full of pests that cannot get out.

Why Insect Netting Beats Spraying on Brassicas

Cabbage family crops attract a short list of pests that arrive by air: imported cabbage worm moths, diamondback moths, cabbage loopers, flea beetles and cabbage root fly. Every one of them has to land on the plant or the soil beside it to lay eggs. A physical barrier takes away that step completely.

Spraying, even with organic products like Bt, works after the eggs hatch. You need to catch each generation, reapply after rain and keep records. On a quarter acre of brassicas, I was spending around six hours a month on spraying and scouting. Netting takes about two hours to install per 100 feet, then a few minutes a week to check.

Choosing the Right Mesh Size

Mesh size is the decision that matters most, and the cheap netting sold at garden centers is often wrong for the job.

For most farms growing kale, cabbage, broccoli and turnips, 0.8 mm is the best all round choice. If flea beetles are not a problem on your ground, the coarser mesh keeps plants cooler in July. Expect to pay roughly 50 to 90 cents per square foot for durable netting that lasts five or more seasons. Thin row cover fabric is cheaper but tears in a season and traps more heat.

Installing Netting So Nothing Gets In

Pests do not need a big gap. A flea beetle will find a 2 inch opening at the end of a bed within a day.

1. Prepare and weed the bed before you transplant. Anything already in the soil is about to be trapped with your crop.
2. Set hoops every 4 to 5 feet, tall enough that leaves will not press against the mesh at full size. Moths lay eggs through netting that touches the leaves.
3. Transplant and cover the same day. Waiting until you see damage means eggs are already on the plants.
4. Leave at least 18 inches of extra width on each side and bury or weigh down every edge with sandbags or soil.
5. Gather the ends, twist them and stake them down like a candy wrapper.

I use sandbags along the sides rather than burying the edges. It makes weeding and harvest much faster, which means I actually open the bed when I should.

The Rotation Problem Netting Cannot Fix

This is where I push back on the advice that netting solves everything. If you put brassicas back in the same bed where brassicas grew last year, you can trap overwintering pests underneath with your new crop. Flea beetles and root fly pupae sit in the soil over winter and emerge right inside your nice sealed tunnel.

I learned this the hard way in a bed I reused for kale. The netting kept new pests out and kept the old ones in, and the damage was worse than in an uncovered bed next door. Netting only works on ground that did not host the same crop family last season. If your rotation tends to slip, read why crop rotation plans fail in the second year before you plan where the brassicas go.

Heat, Water and Weeds Under the Mesh

Netting changes the conditions under it. Most mesh raises the temperature by 2 to 4 degrees Fahrenheit and cuts wind, which brassicas usually enjoy in spring and fall but not in a heat wave.

Watering

Overhead irrigation passes through mesh fine. Drip tape under the netting is better still, because you never need to open the bed to water.

Weeding

Weeds grow faster in the sheltered space. Plan one weeding session about three weeks after transplanting, open one side, work quickly and close it the same morning.

Hot spells

If temperatures stay above 85 degrees for several days, watch for bolting in broccoli and bitter flavor in greens. Coarser mesh helps more than removing the cover, which invites moths straight back.

Checking Under the Cover Every Week

Netting is not a reason to stop looking at your crop. Once a week, walk the bed and lift the mesh at one spot. Look for holes on young leaves, green caterpillars along the midrib and wilting that might point to root maggots. The habits in reading the early signs of a pest problem apply here too, just on a smaller patch.

Check the mesh itself while you are there. Deer, dogs and wind tear holes, and a single 1 inch rip can let a moth in. I carry a small roll of repair tape in my pocket for this.

Other Crops That Benefit

Once you own the hoops and netting, use them more than once a year. Carrots under netting avoid carrot rust fly. Squash covered until flowering avoids squash vine borer and cucumber beetles, though you must uncover it once the female flowers open so pollinators can reach them. Early spinach and chard escape leaf miners. The same hoops can double as frame for a simple low tunnel when frost comes.

FAQ

When should insect netting go on brassicas?

The same day you transplant or sow. Moths and flea beetles find new plants within a day or two, and any eggs laid before the cover goes on will hatch underneath it.

Can I leave the netting on until harvest?

Yes, for brassicas you usually should. They do not need pollinators to produce heads or leaves, so the cover can stay on from planting to the last picking.

How long does insect netting last?

Good quality netting stored dry and out of the sun over winter lasts five to ten seasons. Lighter fabric covers usually last one or two before they tear.

The Practical Takeaway

Pick one brassica bed this coming season, on ground that grew something else last year, and cover it with 0.8 mm netting the day you plant. Seal every edge, check it weekly and compare it with an uncovered bed. One season of results will tell you how much spraying you can stop.