Mulching No-Nos Gardening by the Yard : Episode GBY-806 -- More Projects »
Mulch has a lot going for it--it helps control weeds, maintains soil moisture, stabilizes soil temperature and the organic types promote microbial activity in the soil. Plus, it generally makes the garden look better. "And let's face it," says master gardener Paul James, "mulch makes practically any garden look better." If mulch is not used properly, however, it can be catastrophic. There are two categories of mulch. Inorganic mulches include plastic, gravel and stone. Organic mulches include various chipped or shredded wood products, hay, straw, grass clippings, pine needles, shredded leaves and compost. "I'm not a huge fan of inorganic mulches, especially plastic," says James. Plastic doesn't break down in the soil, it has to be anchored with soil, stones or pins to hold it in place, and in his words, "it's downright ugly." But plastic does control weed growth and help conserve soil moisture.
Plastic also has one distinct advantage over other mulches--it helps warm the soil, which is especially handy during early spring because it enables you to get a jump start on planting (figure A). Covering the soil with black plastic can increase the soil temperature by as much as 10, 15 or even 20 degrees, allowing you to plant warm-season crops such as tomatoes up to four weeks ahead of schedule. Once it has warmed the soil sufficiently, black plastic can be covered with an organic mulch like straw, which keeps the soil from getting too warm and serves an aesthetic purpose as well (figure B). However, plastic isn't permeable, which means the soil doesn't get any oxygen, and that's not a good thing. Worse yet, to thoroughly soak the soil, you have to remove the plastic, install drip irrigation beneath it or punch holes in it, which then allows weeds to grow through it, defeating the purpose of using the plastic in the first place. "Gravel and small stones make great mulching materials," explains James, "but they can be frustrating, even when laid on landscape fabric to make a path, seating area or rock garden, because they get really messy in no time." Leaves, twigs and other garden debris settle on or in between the stones and can be hard to get rid of even with a blower, which can blow the debris and gravel elsewhere.
In his landscape, James uses organic mulches almost exclusively, but they too can present some problems. For instance, he uses straw mulch (figure C), primarily in the veggie garden. But straw often contains seeds of various weeds and prairie grasses. So when you buy hay or straw, James suggests you do one of three things before you actually use it in the garden. Leave it out for a year so that heat and cold have a chance to destroy most weed seeds. Open the bale and let birds gobble up the seeds. Or, put the straw on a compost pile, but make sure the pile heats up to at least 160 degrees, a temperature that destroys nearly all weed seeds. Grass clippings as mulch are fine, but take care not to apply them more than one inch thick. Grass clippings have a tendency to form a dense mat that water and air can't penetrate, which is bad for both soil and plants. "And whatever you do, don't use grass clippings from a lawn that has been treated with herbicides," James warns, "or your plants may well be goners."
By far the most common types of mulches are those made from wood (figure D), but they too can be misused. If piled on top of emerging perennials in early spring, mulch can cause the plants to rot. When placed too close to woody plants, it provides a safe haven for mice and voles to feed on the bark and roots. When piled high around the base of trees, it creates conditions that could lead to rot even in mature trees (figure E). And simply applying too much mulch-- more than two to three inches--can prevent water from penetrating through the mulch, which is why James recommends periodically fluffing the mulch with a metal rake so that it doesn't form a dense mat. Also, too much mulch can prevent the soil from warming up properly in early spring, which can affect plant growth. That's why it's best to wait to apply fresh mulch until late in the spring and then again in the winter to serve as an excellent insulator. Other tips from James: If using freshly chipped mulch, from a city operation for instance, realize that as it decomposes, it zaps nutrients from the soil, mainly nitrogen. Either compost the chips for several months first or apply a high nitrogen fertilizer such as blood meal over the mulch. Also make sure you know the source of the chips because some may actually come from diseased trees or worse yet, from walnut trees that contain a substance called juglone that's toxic to a number of other plants. Pine straw and oak leaves make great mulches, but they acidify the soil over time, so use them only in and around plants that require acidic soil, such as azaleas or blueberries. Consider where you live when deciding which mulch to use in your garden. After all, shredded wood products might look completely out of place in a desert landscape, as would gravel used to mulch an evergreen bed in the Pacific Northwest. "I still think the biggest mistake you can make when it comes to mulch," concludes James, "is not to mulch."
| |
![PHOTO](javascript:popup("http://img.hgtv.com/HGTV/2003/08/08/gby806_1a_e.jpg",350,450))
![PHOTO](javascript:popup("http://img.hgtv.com/HGTV/2003/08/08/gby806_1b_e.jpg",350,450))
![PHOTO](javascript:popup("http://img.hgtv.com/HGTV/2003/08/08/gby806_1c_e.jpg",350,450))
![PHOTO](javascript:popup("http://img.hgtv.com/HGTV/2003/08/08/gby806_1d_e.jpg",350,450))
![PHOTO](javascript:popup("http://img.hgtv.com/HGTV/2003/08/08/gby806_1e_e.jpg",350,450))
