Weed suppression

Asked April 19, 2020, 6:43 PM EDT

Hi. I planted New Zealand Clover last October over a wide area, which I had cleared of weeds and grass. I followed instructions for planting. I also planted the clover in my raised beds. The clover started to grow in October, then disappeared as the weather got wetter and colder. Come March/April and all I have is a thick carpet of hairy bittercress--EVERYWHERE! I've never had this happen before and I don't know what happened to the clover. Any ideas, suggestions? Thank you.

Multnomah County Oregon

1 Response

Cover Crops can be very beneficial in your garden. By growing and covering the garden soil they block light from winter germinating weeds so the weeds never get started. Even the ones that do get started are smaller and easier to pull. They also protect the soil from hammering rain, and add organic matter when incorporated into the soil.

To get a good cover crop the plants need to be well established before the weather turns cold. Seeds need to be sown in late summer or early fall, while the soil is warm enough for good germination. Then, at least 4 weeks of good growth before cold weather restricts that growth is needed. Sow your clover seeds in late August or early September and you'll have good results.

Bittercress and other mustard weed seeds can remain viable for decades in the soil. If given a chance they will germinate over winter - and you'll see the results, especially in bare soil, the next spring. Your plan to use cover crops is great. You just need to get the plants going earlier and you'll see good results.

This article has additional information on cover crops, Cover Crops for Home Gardens https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/fs304.pdf. By the way you can also achieve good results with a mulch applied in the fall. Shed leaves make great mulch