Mulch offers plants’ roots much needed shade

6/19/2013

When it seems so hot that you could probably fry an egg on the sidewalk, you can almost believe that you could fry another one on exposed garden soil, too. At any rate, that soil can get hot. And then we ask young, tender plants to grow in such soil — material that heats up under the super-dry surface. These conditions are brutal and can be traced to many vegetable-garden failures.

Shade always helps, of course. But your plants need full sun to grow, so you can’t put up an umbrella to cool off the ground. Truth be told, only the roots need shade. The traditional solution is to spread straw over the ground as a mulch around each plant to create an insulating layer that protects the soil from direct solar exposure.

The word “mulch” describes a specific type of material that is nonspecific in its origins but functions much like goose down in a winter coat. Down retains its loft to create a thick zone of dead air for maximum insulation. In the garden, folks have long used mulch around their vegetables to create a similar insulation layer between the sun and soil to keep conditions underground cooler.

Mulch does other things provided it’s 2 inches deep, and preferably more. First, mulch prevents surface crusting of the soil so water introduced goes straight in. Second, it shades the soil so roots will find a sizable zone of cool rich soil. Third, mulch laid thick enough cuts off light to the soil surface, denying weeds incentive to grow. You can also use mulch in pathways through the veggie garden to keep your feet clean while watering or picking.

Mulch is not a soil amendment because the best materials resist decomposition. If they are tilled in, you risk nutritional problems in the soil because the lignin in these cell walls is hard for microbes to break down. They may even rob the soil of its nitrogen to help in the decomposition process.

You can reuse mulch season after season. In late fall, rake mulch off your garden and into a pile for reuse. It’s great for freeze/thaw mulching after the first frost, or just stockpile for the following year’s food garden.

Straw is the most common mulching material because it’s widely available at feed stores, and it’s cheap. A single bale can cover even a good-sized garden with plenty of insulation for plants and pathways. Even if there’s a lot of rain and mud, the straw holds its loft because it doesn’t get soft.

Look for mulches you can obtain for little or no money, such as wood chips from green waste programs. Every corner of America will have its own mulch sources. In the South, pine-needle straw is used on ornamental and food gardens because it’s so plentiful there. The Northwest is full of lumber mills making sawdust easy to get, but you’ll find it in every cabinet maker’s shop, too. Nut hulls, rice hulls and ground corncobs are agricultural byproducts that are plentiful in regions where these crops are grown. You can even save autumn leaves for next year’s summer garden mulch.

Mulches aren’t laid out until the soil becomes warm enough and plants are under way. Put it on while it’s cool and the soil won’t heat up enough properly to germinate your seeds or stimulate seedling growth. Keep your mulch layer at least 1 inch or more away from the base of the plant to avoid stem problems.

Mulches aren’t always the best-looking part of the food garden, but they are among the most essential to enhancing plant health. Nothing works better for water conservation. Too, they help eliminate weeds.

The best news? A well-mulched garden means you’ll have more time to go to the beach or a baseball game -- rather than staying home to weed.