I am a big advocate of mulches. If I didn’t use mulch, I could never keep up with the weeds. My fruit trees and shrubs get mulched with bark or wood chips, and I mulch the perennial beds with cocoa shells or compost. But when it comes to the vegetable garden, mulching gets a bit more complicated.
Over the years, I’ve mulched my vegetable garden with oat straw, newspaper, grass clippings, burlap coffee bags, leaves and black plastic. There was no particular method behind my madness. It was a matter of using what was available. Results were mixed. The straw looked great, but was expensive, and also contained so many seeds that I had to weed out foot-high oat plants for most of the summer. The newspaper blew around and looked terrible. The grass clippings came from a late-spring mowing and within three weeks, I had grass growing throughout my vegetable garden.
Burlap bags were effective. I put them down in the pathways over sheets of newspaper. The garden looked a bit like a rummage sale, but the bags kept the weeds down. I also tried mulching with leaves. Most of them blew away, except in the asparagus bed, where they work pretty well. Black plastic mulch has yielded some good results and a few disappointments. I’ve had some great sweet potato and melon crops. But it’s a bear to put down (and keep down) when the wind is blowing; it doesn’t let rainwater into the soil; and at the end of the season there’s a lot of plastic for the landfill.
With all this experience to draw from, I now try to match the mulch to the crop, weather conditions and soil. University field tests have shown that mulch can increase (or decrease) yields by as much as 30 percent, so it’s worth thinking through the options.
Not all vegetable plants like the same growing conditions. Heat-loving peppers, tomatoes, eggplant and melons are great candidates for black plastic mulch. Applied in early spring, the plastic will raise soil temperatures and help warm the air around the plants. But most plastic mulches are not water-permeable, which means that as the season progresses, your plants may go thirsty. Inadequate moisture can stress your plants, lead to blossom-end rot problems on tomatoes, and diminish your overall harvest.
If you expect plenty of rain or intend to use overhead irrigation, your plants’ roots may be able to get the moisture they need from the pathways. Another solution is to install a sub-surface irrigation system beneath the plastic mulch. You might also consider removing the plastic in late July and replacing it with a water-permeable mulch, such as straw, newspaper or grass clippings. This mulch will allow rainwater and overhead irrigation to get down to the root zone, and will also help retain moisture.
Cool-weather crops, such as broccoli and greens, don’t want the extra heat from a plastic mulch. They’ll be better off with straw, shredded leaves, paper mulch or newspaper. These mulches can lower soil temperatures by as much as 20 to 25 degrees, which may keep cool-weather plants producing right through the summer’s heat.
If you live in a hot climate, use plastic mulches judiciously. High soil temperatures can stress your plants and burn up organic matter. In hot climates, most crops will be happier and more productive with a soil-cooling mulch such as shredded leaves or straw. Conversely, if you live where summers are cool and wet, using a moisture-retentive, soil-cooling mulch could be disastrous. You may find your plants stunted from the cold, turning yellow from too much moisture, and being chomped by an army of slugs.
Make sure to let the soil warm up and dry out a bit before applying soil-cooling mulches. Depending on where you live, this may mean waiting until June or even early July. Consider using a plastic mulch during early spring. It will raise the soil temperature and also help dry out the soil.
Take a minute to consider your garden’s soil conditions before selecting a mulch. Most vegetable plants perform poorly in heavy, wet soil.
This type of soil will usually dry out a bit as the season progresses, so don’t cover it up with a thick, moisture-retentive mulch. Nor should a dry, sandy soil be covered with plastic mulch, because it would prevent rain and irrigation water from seeping down to the roots.