Weed Free Brassica Cage Setup

For years now I’ve grown the bulk of my leafy brassicas under nets. Now I’ve made it virtually weed free as well as pest free.

The Brassica Cage

Growing leafy brassicas like cabbages, cauliflowers, calabrese etc. under netting has two benefits.

Firstly the netting keeps the pests away. The two main pests being birds and butterflies. In a bad year for butterflies it’s almost impossible to keep up with the amount of eggs being laid and caterpillars on the brassicas without resorting to chemicals. I don’t like using pesticides and particularly onto the part of the plant I’m going to eat. Netting isn’t perfect but it makes it easy to keep the crop pest free without chemicals.

Secondly the micro-climate is slightly better in the cage than out. The wind isn’t stopped but it is reduced in power. This reduces wind chill, effectively making the temperature on the plants warmer. It also prevents wind-rock. This most effects Brussels sprouts but also any of the larger leafy plants. The wind rocks the plants and this damages the roots preventing the plant from absorbing sufficient nutrients to fuel growth.

Cage Construction

The easy way for me was to buy a cheap polytunnel off Ebay. I could have built something with a wooden frame but there was little difference in cost. And that was before the recent price hikes in wood and building materials.

The galvanised metal frame was easy and quick to erect for two people. It’s durable although I don’t expect it to last as long as my proper polytunnel frame. The scaffold / windbreak netting was also bought off Ebay and attached to the frame with cable ties.

The supplied polytunnel skin could have gone over the frame but I don’t believe it could stand up to the high winds we get here. The netting allows much of the wind to pass through where a polytunnel skin doesn’t. The full wind force acting on the polytunnel skin would probably buckle the frame and destroy it.

Incidentally, my First Tunnels Polytunnel has a much sturdier frame and stands up to everything nature throws at it here.

Brassica cage, roughly weeded

Weed Control

Inside the brassica cage the weeds were growing well, so a quick hoeing and rough raking out got it as the photo shows. If I was planting into that normally, I’d want to do a better cleaning job.

Next we laid out non-woven weed matting. I’d bought a piece the correct width and twice the length needed on Ebay. Cutting it in half using a gas powered hot knife so the edges didn’t fray only took a couple of minutes.

Planting Holes

I’ve a range of different brassicas going into the tunnel and they have different spacings. For example:

  • Minicole Cabbage 12” (30cm)
  • Hispi Cabbage 15” (40cm)
  • Calabrese 18” (45cm)
  • Sprouts 30” (75cm)

The matting will last for years and the mix of plantings will change so what to space the holes at? I decided to go at 18” spacings. Some things will have more room than needed and by leaving gaps others a bit more or less. I can also plant cabbages that don’t need much space next to brassicas that need more. It’s not perfect but should be good enough.

I could have made holes at closer spacings but that would weaken the matting, reducing its life. It would also mean lots of vacant holes growing weeds.

Hole Cutting in Weed Matting

I made a simple template from a piece of scrap plywood by cutting holes at the correct spacing with a hole saw. Bending down to move the template lots of times is not the best thing for my back so I fixed an upright handle to the template.

Me and my no-bend hole template

Using the weed burner to cut the holes didn’t take long – this video is me burning holes for some squash last year. My son-in-law made this video clip of the process on his phone.

Holes Cut, Ready to Plant

It looks rather good with the matting well anchored using staples and all the holes made.

Weed membrane laid, holes burned and ready to plant.

Planting Up

I like to bring my brassicas on in pots prior to planting out. To minimise root disturbance – which doesn’t really matter too much with brassicas – I use a bulb planter to make a hole and then pop the plant in.

Brassica Cage Planted Up (More to plant soon!)

A Pest Problem

Perhaps a mole under the membrane

I’ve defeated the weeds, kept the birds and butterflies at bay but nature had another trick. A mole under the matting!

I think it’s a mole as a couple of plants were pushed out with a pile of soil. Not a massive problem but an irritant all the same.

Basically I shouldn’t need to spend hardly any time on cultivation until harvest time.

Posted in Allotment Garden Diary
18 comments on “Weed Free Brassica Cage Setup
  1. Chris Durrant says:

    Hi John, that is one very good idea! I have a load of this matting left over from a previous job & wondering when I’ll get to use it. I especially like the idea of the hole template & weed burner, but I’m curious – the construction netting doesn’t seem to have any eyelets in the usual run of black joining seams, like I have always bought. These eyelets are a pain, as although birds & butterflies won’t get through them, aphids like blackfly, whitefly etc. can, albeit in reduced numbers. Is it that you have aligned the eyelets along the hoops or have you found construction netting without those seams with eyelets in? If so, I’d be interested to know where you got it from. Regards,

    PS. That capillary matting automated irrigation system I mentioned to you a couple of years ago worked a treat. What a time saver.

    • John Harrison says:

      Hi Chris
      I just used cheap windbreak (scaffold) netting bought off Ebay. The cable ties are pushed through the netting weave and around the frame. There are no eyelets on this netting used.

  2. Theresa Jessey says:

    Hi John, I was very interested in your project as I do a similar thing for my brassicas. However, like Chris, I get aphids on my plants. I have used a netting that aphids can enter through but found the scaffold netting didn’t do much better!

    I will certainly show your article to my son and see if we can’t copy it as you can at least stand up in your tunnel – we have to undo the sides of ours to weed etc. I don’t like using the weed suppressant because it is difficult to feed the plants through the planting holes (we tried it on our strawberry bed). I also wonder if you will move the tunnel around your plot each year and how difficult this will be?

  3. Jeremy Quinlan says:

    That sounds wonderful but what about crop rotation? Surely it is bad practice to plant essentially the same crop in the same spot year after year. Or do you plan to move the brassica cage every year?

    • John Harrison says:

      I’m topping up the soil with a large amount of manure so in effect, part rotating. I figure I can move the tunnel every 3 years (takes 4 people to avoid bending the frame)

  4. david arthur lamb says:

    hi i have done it with growing onions, holes 6inch apart, i cut them with a small gas blow torch, warmed a small tin, (mushy pea can is ideal just hold it with mole grips and it burns through, with no frays,) it works well the only weeding you have to do is around the onion bulb

  5. Jim Ferns says:

    Hi John,
    I use the black membrane to grow squash, sweet corn and French or climbing beans. I also use it to grow brassicas. All are transplanted and then covered with a 2 litre plastic bottle with the top and bottom removed forming a cylinder around the plant making it easy to water an individual plant. Any slugs/snails have to climb up and down the bottle giving time to spot them.
    I have used fish boxes to act as mini cold frames and found that the slugs/snails cannot travel across the polystyrene. The liquid they use to slide along is absorbed by the polystyrene.
    Jim Ferns

  6. Frank Croall says:

    Hi John,
    Have you had any issues with the scaffold debris netting becoming brittle?
    I have used this on a smaller cage made in the spring(32mm blue water pipe covered with net and attaching with tie wraps) however the netting at the tie wraps is now ripping
    Any tips to prevent this?

  7. Rob Thomas says:

    Hi, thanks for the useful article, would it be possible to provide a link(s) to the poly tunnel and netting that you used. there are literally hundreds on the ebay site, so unsure which to choose. Does the poly tunnel come in different sizes, the biggest length I can accommodate is approx 3m. Thanks.

    • John Harrison says:

      The suppliers change frequently – probably to avoid guarantee problems! Look for a galvanised steel frame. Yes they come in different sizes. Pretty much of a muchness with green scaffold netting.

  8. Alan Dolman says:

    Using a weed free brassica cage do you move the cage each year or add new soil

    • John Harrison says:

      It is moveable but I’m fortunate to have massive amounts of manure so I can refresh the soil with that. I think it would be best to move it after some years – maybe 3 or as long as 5.

  9. Ruffy Ruffles says:

    An interesting observation for this season’s early brassicas…
    A mixture of cabbage both pointed and round, calabrese and cauliflower planted in the netted cage on 30/03/23.
    A similar mixture planted outside under fleece on 12/04/23 have not only caught up but have passed the caged plants and are further ahead, nearly ready to harvest.
    Not the first year this has happened and I suspect the green cage netting is absorbing some sunlight thus reducing the rate of photosynthesis amongst the caged plants.

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