Tenacious Weeds in Garden - Knowledgebase Question

San Diego, CA
Avatar for wjeaston
Question by wjeaston
January 17, 1998
I have some kind of grass growing in my vegetable garden I can't get rid of. It grows like wild fire when it gets water. I have tried black landscaping fabric--it grows under and through it. I tried mulching almost a foot thick with straw, it still comes up. I've tried using weed killers on it, it dies but them comes back up when I start watering again--even months later. This is a raised bed garden and the people before us apparently got the soil from a river bed. We have added lots to it and it's great soil but I can't grow anything there for long because the grass takes over. It seems to regenerate from a tuber-like (but hard like a nut shell) thing that the roots come out of when watering is resumed. We have tried to remove these tubers when digging up the garden but there are thousands of them. This last year we didn't even have a garden because controling this grass makes it too labor intensive. We are considering throwing away all the old soil and building a new raised bed with brand new soil but this can get spendy since the old one is 24'x 48'. We will do this if we have to but wanted to consult the experts for any other ideas.

Answer from NGA
January 17, 1998
It sounds like quite a problem. You might contact your local Cooperative Extension office (ph# 619-694-2845) to see if they can help you identify the culprit, and see if perhaps they have some speciall tricks to combat it.

Here are a few thoughts: One trick I use is to lay down a thick layer of newspapers (or corrugated cardboard) first, then top with mulch. And I mean thick--not just a few sheets but a layer 1/2-1 inch thick.

Another option might be soil solarization. This will put the bed out of commission for one summer, may not solve the problem if indeed the plant has tenacious rhizomes, and will kill lots of good soil organisms, but you might give it a try. To solarize soil, first turn the soil over with a garden fork or spade, thensmooth the surface. Water the site until it is soggy. The next day, cover the area with clear plastic--3- to 6-mil is best--and bury the edges so it won't blow away. Seal it well so no fresh air can get under the plastic--you want it to get good and hot. You'll be effectively cooking--steaming!--the weeds. Then simply leave the area covered through the hottest part of the summer--at least July and August. (Soil solarization works best in warm climates.)

Finally, you might try one of the new organic pre-emergent herbicides. WeedzSTOP is a corn gluten-based herbicide that inhibits seed germination of tough weeds. Note that you would not be able to plant seeds in areas treated with this herbicide, but it won't affect transplants or bulbs. (WeedzSTOP is available from Gardener's Supply, ph# 800-863-1700, web site: www.gardeners.com)

Maybe a combination of these tactics will work for you. I hope so!

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