So, Paekakariki growers, I come to you for ideas... what are your theories on black plastic and kikuyu grass? I've made a couple of raised beds about a foot above the ground with bricks, and had filled one with a mix of compost and topsoil before a neighbour dropped by and offered me some black plastic to line the other two beds - he said it was the only way to go, otherwise that kikuyu grass would take over before my eyes.
But lo! Things aren't really growing in those lined beds, while the unlined raised bed is doing all sorts of wonderful with carrots, Brussels sprouts, silverbeet and broccoli all going great guns. The carrots are a case in point actually - I planted four rows in each bed and the lined bed ones have done nothing since they germinated.
Things just look a lot happier on the unlined side of the path. Do you think it is to do with worms? Drainage? (I did put an awful lot of holes in the bottom with the rake). Yesterday I took a lot of the sad looking plants out of that bed and put them in with some happy plants, but as there is a cauli doing well I lost some of my enthusiasm for pulling everything out and removing the lining.
My gut feeling is to remove the plastic, but as I had never met kikuyu before this year I thought I'd ask some local locals...
I have a lot of experience with that beastly grass... trust me, I've broken several garden implements battling the stuff. The only solution as far as I can see is some serious digging... and more digging. My technique is to first kill off as much as poss by laying old carpet over the kikuyu patch that I want to get rid of. I'd guess that black plastic would have the same effect -though the weight of carpet stops it blowing away in the first breeze. In some serious cases I have left the carpet down for several months first. This serves to weaken and kill off quite a lot of it. The other benefit of this is that the ground will become nice and moist and easier to dig over. You then need a strong garden fork to dig out all the roots. I find you need to dig up to a foot deep to catch all of it. It pays to dig it over a second time to catch the bits you missed.
For really entrenched stuff... like an established lawn, I use a grubber to chop off the top layer (more physical than chopping firewood!)
In the end I think it's really worth the effort up front. I've successfully managed to make a lot of my garden kikuyu free now. The idea being that if you're not going to really get rid of it properly, you may as well not bother because it grows back so quickly you'll eventually be defeated.
Some people even go to the extent of digging in a plastic barrier down to about a foot around their garden beds to stop those roots getting through. I know someone who has covered the pathways between his raised beds with carpet and then put a covering of bark chips over the carpet (shells would have been nice too).
I hope some of that helps...
Do pop by to chew the fat on your favorite worst weeds whenever you like!