Weed control these last months – couch grass

The last of the three Big Weeds I’ve been working with this year is couch grass. Couch is a funny one, because I wouldn’t actually mind having some patches of lawn here and there. It’s just so invasive that I really do need to remove it from almost everywhere – its ability to spread over distance is massive. I’ve spent a lot of time over the couple of years I’ve been here studying it, where it likes to grow, how it grows, and trying different methods to knock it back or out. And I’ve learnt a lot.

For instance, you *can* dig it out of an area completely. You need to be thorough, because couch has lots of little joints each of which develop soil-gripping roots, so it’s easy to leave bits behind. And any bit you leave behind will just keep shooting new growth, and shooting new growth, and so on. Couch is like this hive mind of a plant, it acts like a single entity but it’s really made of hundreds of individuals. You gotta get them all. But, if you do, it’s pretty much gone from the area. Just weeding by hand doesn’t usually get it all, but digging and soil sifting does. Any areas I’ve dug it out from I’ve pretty much managed to clear. The exceptions are spots where it’s gone low – more than 30 cm deep, and couch is known for sending its stolons and runners down to 60 cm depth in very sandy soils like mine. It’s a lot of digging. I lost one of my infrastructure trees in zone 1 this year because it couldn’t handle the repeated root disturbance from my trying to get one lot of couch out from under it about six times.

“Windowing” – laying a glass window over the top and letting the sun’s heat burn/cook the soil – gets a lot of the couch, but not all. It can only really heat the top ten to fifteen cm of soil. So it will take out annual weeds and tussock grasses, but runner grasses like couch have the ability to escape  the heat. After all, that’s part of the reason couch lives through our summers anyway. You know those brown, brown summer lawns that then suddenly revive when it rains? That’s couch. However, I’ve used windowing successfully to cut down the amount of couch in an area, which reduces the amount of work, materials and time I have to spend on any other method.

Mulch-and-cover is a method good for removing many plants in bulk, and it’s been the most effective method on the oxalis. Put some cardboard down, cover it thickly with mulch, that lot of soil gets no light and substantially reduced water plus has a barrier to growth that prevents flowering and seedset should a weed germinate anyway. However, it’s exactly the wrong way to deal with couch. Couch *thrives* on this kind of environment. They don’t need flowering or seedset. And, those stolons are surprisingly strong. They will pierce and grow directly through wood chips, old wood, any organic matter in the soil. In fact, they love doing so so much that you can use the presence of old mulch layers to predict where couch will spread. In Zone 1 there’s a section that was obviously mulched when this house was last sold some six or seven years ago now. The mulch is long broken down, but it left a layer of soil above the sand that was much more woody and with very little sand content. The couch that invaded from next door filled that area completely and thickly within four years, but put out only the odd surface streamer into the sandy area right next to it. I was able to keep it contained to that space quite easily until I got around to removing it all a couple of years later. There’s another spot in zone 4 that was a constant source of couch, and when I finally got to digging through it this year I found old rounds of timber just under the soil surface – a long forgotten natural-material paved area. We did try mulch-and-cover in a couple of spots in my first year, but the couch grew back the next season thicker than ever.

I ended up giving in on my principle of “no poisons”. I could remove most of the couch from everywhere by other methods, but I couldn’t get it all, and you need to. I did look briefly at alternative sprays to commercial weedkillers, however the commercial options were mostly aimed at broadleaf weeds and maybe some grasses but not couch. Couch is widely acknowledged as tough to kill. The most likely possibility was a urine wash – keep urine in a bucket for three days until the nitrogen has transformed into the most plant-killing form possible, then put that on the leaves. It kills plants, but also becomes fertiliser in the soil. However, I decided to not try and apply that across the entire areas of couch I needed to remove. I wanted something reasonably reliable in one hit. So, that left glyphosate. Which I was sure would be systemic enough to get down a couch runner to knock out the buried stolons – most of the alternative sprays couldn’t do that, they really only killed whatever part of the plant they touched.

I did a test batch on a section of Zone 1 in December, shortly before we were due to go on holiday for three weeks. It didn’t seem like anything happened, but when we returned from holiday it had clearly been effective. So then I experimented with other preparation strengths and timing across the summer and autumn.

What I learnt:

  • Mix your own. The pre-mixes aren’t strong enough to reliably take out couch. I see no point in repeatedly using weak poisons to no effect when a higher strength does its work and has done with it.
  • Secondsummer – mid-January through February to about mid-March – isn’t a good time for spraying. The couch is in drought/heat mode. Any bits of it above the surface have the stomata shut down and the leaves in narrow-folded-light-protection mode so it can’t absorb enough of the spray. Much of it is dormant below the surface and you aren’t getting the spray to that lot at all.
  • Firstsummer – late November, December and early January – is a great time for spraying couch. All my wanted annuals have died back with the onset of warmth. The couch however *loves* the warmth and the soil structure’s still full of moisture so it’s doing some of its best growing for the year. It’s at it’s most susceptible, and many of my other plants are least-susceptible if not completely absent so I don’t have to worry about killing other species accidentally.
  • Early autumn – from mid March through to about the end of April – is also an OK time to get the couch. Results are slow, because the couch’s growth is slower with the increasingly short days and cooling temperatures, but it *is* growing after that first rain that marks the start of autumn in the six-season calendar, and any buried bits are starting to resurface.
  • Makuru or winter is not a terribly good time as there’s heavy dew most days if not actual rain, which washes the glyphosate off before it can have enough effect. I will try one spot during winter though – under the grapevine. It grew too thickly in summer to be safe to spray next to. So I’m waiting for it to lose its leaves so as to avoid it catching the spray too. We usually have at least one rainless week during winter and I’ll try then and see how I go.
  • No matter what strength I spray with or when, I don’t see if it’s working for two weeks, and it takes three to be sure it’s actually had an effect. Patience, Grasshopper.

In Zone 4 I still used every other method I had to knock out couch first, so as to reduce the amount of poison needed and manage the overall risk to the systems I’ve been setting up. A combination of digging/weeding followed by mulch-and-cover has been good, because it does get most of it but then you do clearly see where any bits you’ve missed are coming back up. It made it very easy to wander around with a tiny spray bottle and just get this bit here, that bit there. Zone 1 I sprayed without other techniques, because there were existing plants I couldn’t disturb but with great areas of nothing but couch between – far too much to dig knowing how long the sections I *had* dug had taken me for how little result. I decided there I also wanted the dead couch to remain in place to protect the upper soil layers until the Zone 1 system spread itself into those spots, so spraying without digging made more sense. Where it does regrow again, I don’t mind a little dig/weeding to pull out a runner or two, it’s easily containable once there’s only a little of it. And (with permission) I also sprayed the section of my neighbour’s rock-rubble verge that had been invaded by her couch grass in the first place, so now there’s a wide barrier between my zones and reinfestation.

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