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Summer is finally here, and the tomatoes and peppers are in their element. Mulching the garden now will help keep moisture in, moderate temperatures and shade out some weeds.
"The most basic division among mulches is that some are inorganic and some are organic," says Ward Upham, horticulturist with K-State Research & Extension. Any organic mulch is better for plants, soil and air-conditioning costs, he says.
Here's a look at some of the choices Upham gives in both categories.
Inorganic mulches
Among the materials: black plastic sheeting, fiber mats, gravel, pea gravel, pebbles, river rock, lava rock, and chipped or shredded rubber tires.
What sets the tone is how the compost blends, complements or contrasts with native rocks and soil, K-State says. The look can range from natural to exotic to near-alien.
"Because they last longer, inorganic mulches tend to cost more than the average organic product," Upham said. "But the rock-like types also trap empty spaces as they pile up in a layer — spaces that will gradually fill up with mud from below and with debris and seeds from above. At the very least, you have to put porous weed-barrier fabric under them, to keep the rocks from slowly sinking into the ground.
"If they get kicked or cat-scratched out of place, the rock types also can be a mowing problem. And, if you ever change your mind, the fabric and inorganic mulch will be hard work to remove."
If layered deeply, rocks will help control weeds, but they also can damage plant roots because they absorb and reflect heat, Upham said. They speed evaporation and can require more watering. Next to a house they can also add to cooling costs. Shiny and/or dark materials tend to be the worst, K-State says.
Upham gives a couple of warnings:
* Gravel has a high pH, which can cause chlorosis or iron deficiency in susceptible woody plants.
* Rubber mulch can contain bits of steel from radial tires and burns hotter than wood mulch. The fire is harder to put out and can cause allergic reactions. Research is being done on whether the breakdown of the rubber slowly harms plants.
Organic mulches
Because organic mulches break down, they enrich the soil and improve its structure as they decompose.
In general, the smaller and finer the pieces, the more often they have to be replenished, he said. Peat moss is so fine it makes a better soil additive than a mulch. Cottonseed hulls, crushed leaves and sawdust also can be hard to keep in place, though the leaves and sawdust can compact, too.
"You have to be sure organic mulches aren't contaminated by weed seeds, which can be the case with some straws and hays that haven't aged for several years. Composts can have that problem, too, if they aren't fully 'cooked.' "
Many people use chipped or shredded wood. Big, coarse pieces and pest-resistant woods such as cypress and cedar last the longest.
"If you use a mulch that may contain nonresistant woods, you shouldn't pile it deeply or plow it in later," Upham said. "You shouldn't even think of placing it in contact with your house."
Lawn clippings that have been dried out for several days can be used as mulch, Upham said. Just be sure you've mowed four times after using a herbicide before using the clippings. (If quinclorac, or Drive, was used on the lawn, just let the clippings go back into the lawn.) Use no more than 2 to 3 inches of clippings for mulch.
If you use grass clippings or another freebie, shredded newspaper, you can cover it with a shallow layer of better-looking mulch, Upham said.
Sheets of newspaper, laid flat on the ground, can act as a weed barrier as well.
