When you put away a gallon of paint or the leftovers from dinner, you always cover the container. By sealing the paint can or plastic storage container, you lock in moisture. It keeps your paint from drying out. Same goes for your spaghetti with pesto (not to mention sealing in the “aroma”…).
Your plant roots can benefit from their own covers, and that’s where mulch enters the picture. Much like the top layer of paint in a can, air dries out the soil at ground level. Add wind and heat, and water can evaporate quickly from desert gardens in particular. Mulch helps insulate the soil to keep it cool and minimize evaporation. The layer of mulch also protects the area around the plant’s roots from the forces of nature. In other words, when the rain comes, it won’t pound the ground, eroding dirt away. Instead, it hits the layer of mulch, then trickles down to the ground. Use an organic mulch and each time it rains or you irrigate, the water carries some nutrients for the roots to take into the plant as well. Need more reasons? Mulching cuts down on weeds, and weeds compete with your plants for water. Plus, they are such a pain.
To truly insulate and cool plants takes about three to four inches of mulch material. It depends on the type of material you want to use. If the mulch is fine, such as bark cut to smaller than an inch in size, go only about an inch or two deep. The same goes for grass clippings. Your roots also need some air to thrive! So be sure to avoid use of landscape plastic under your mulch in any areas where you will plant. The plastic is great in walkways, but not in your beds or under trees.
When piling mulch around plant or tree roots, cover the entire area to which the roots extend. For trees, you need to go out about as far as the tree’s canopy. And don’t place the mulch all the way up against the trunk of the tree or stem of the plant. Leave a small opening close to the plant.
Mulches also can look attractive and add to landscape design. Be careful about mulches you choose and social media posts with ideas for repurposing materials as mulches. Some are harmful if applied directly to vegetables and other plants or introduce weeds to your garden. And if your helpful neighbor offers fresh chicken or horse manure, remember that you shouldn’t apply it hot. Add it to your compost, and eventually to the vegetable garden.
We’ll break down some types of mulch in a future post, but if in doubt, check with your local extension office or master gardeners.