Have you experienced one or more of these garden scenarios?
- It’s early April and chickweed, henbit and other winter annual weeds are growing so thickly in a vegetable or flower bed that the soil can’t be seen.
- The winter rye cover crop you mowed last week is growing back.
- You tilled and raked a bed that you couldn’t plant right away and now weeds are coming up everywhere.
- The rainy summer weather is favoring weeds over crops so that the weeds are taking over walkways and dominating beds that you want to plant with fall crops.
- Neighboring plots in your community garden have been abandoned and weeds are growing wild and reproducing!
Un-controlled weeds compete with garden plants for water and nutrients, are hosts for insect pests and diseases, and can demoralize the toughest gardeners. Tilling, pulling, chopping, and hoeing are all fine weed control techniques under the right conditions, but they also disturb soil allowing even more weed seeds to germinate and flourish.
There’s another way: occultation. The common dictionary definition is “an event that occurs when one object is hidden by another object that passes between it and the observer.” For gardeners and farmers, it’s covering the soil to create a dark, warm, moist environment. In 2-4 weeks, this no-till technique can:
- smother and kill young weeds
- smother larger weeds and grasses
- accelerate the decomposition of mowed cover crops and weeds
- promote the germination of weed seeds and then smother the seedlings
When the cover is removed you are left with a mat of decaying organic mulch. New weeds will be fewer because the soil was not disturbed. Spread a 1-inch layer of compost and you’re ready to plant seeds or transplants. Of course, you could plant transplants through holes cut into the weed barrier.
Gardeners can use black tarps or weed barrier fabric. Some farmers use black silage covers (new or used). Weed barriers allow water and air to penetrate while tarps and silage covers are water-resistant. I’m not aware of research that has compared the types of covers used in occultation. I’ve had good luck with heavy-duty woven polypropylene weed barrier fabrics (they last for many years). Four-foot widths work well for most gardens and strips of the fabric can be overlapped for wide beds. It’s important to completely cover the target area and pin down the edges of the cover with landscape staples, bricks, or soil. If possible, weed-whack or mow the weeds first. DO NOT cover the fabric with any organic material. Weed seeds will germinate on top and grow roots down through the weed barrier.
By Jon Traunfeld, Director, Home and Garden Information Center
Additional information: this technique was explored in a research project by Jerry Brust, Ph.D., IPM Vegetable Specialist.