Gardening Guru: It’s Time for a New Layer of Mulch

Did the long Labor Day weekend give you a chance to catch up on gardening chores? Or do you plan to get fall cleanup done this coming weekend? Whenever you do your fall cleanup, make sure the last thing you do is add some mulch to your garden.

Probably the most important reason to add mulch to your garden in the San Joaquin Valley and the foothills is to keep the hot sun from hitting the soil directly and drying it out. While it serves to insulate the soil from the sun, it also reduces the soil temperature fluctuations, keeping roots cooler in the summer and warmer in the winter. This reduces plant stress and improves the plant’s appearance. Mulching prevents crusted topsoil from forming that may cause water to run off into curbs, gutters or sidewalks. And perhaps the best reason to cover soil with at least a two-inch layer of mulch is to suppress weeds, by blocking light needed for germination from reaching the seeds.

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Mulch is anything that you use to cover the surface of the ground. Mulch is often confused with compost. While compost may be used as mulch, its primary use is as a soil amendment. Compost is worked into the soil when creating a new flowerbed, planting seeds or transplanting a new plant.

Mulch minimizes the evaporation of water from the soil surface and reduces the need for irrigation by as much as 50%. Over time, it will decompose and improve the structure of the soil. When used regularly, organic mulch will decompose and release its nutrients into the soil, reducing the need to fertilize. It also helps to support earthworms and soil microorganisms that add to good soil tilth. An additional benefit of mulch is that it can increase the soil’s ability to retain water.

Karrie Reid, a UC environmental horticulture advisor in San Joaquin County, talks about mulch in her article titled “Mulch” in the Retail Nursery and Garden Center IPM News. Reid recommends adding mulch to large landscape pots and planters. Large pots for small trees, shrubs, topiary, or seasonal color benefit greatly from the addition of a one- to two-inch layer of organic mulch. Water use is significantly reduced by covering the pot soil.

Reid cautions not to use mulch right next to the street curb. In heavy rains, the mulch could float away, clogging storm drains. This creates an excess of solid material that is carried into the storm water system.

How much mulch do you need to apply? Reid recommends that organic mulches, such as weathered sawdust, straw, lawn clippings, or other such materials, be applied two to four inches deep on the soil. Shredded “gorilla hair” type products entwine and hold together best on slopes. Use smaller nuggets or chipped wood, ¼” fine with smaller plants like annuals or perennials. Larger chunks are best used in windy areas because they will stay put and are a good choice for landscapes and under trees.

So, how much mulch do you need to buy to cover your bed with a two- to four-inch layer? First, measure the area you want to mulch in order to calculate the square footage. Multiply the width of the bed by the length of the bed to determine the square footage of your area. Then, check the coverage specified on the bag of mulch you plan to use.

Most retail nurseries and garden centers sell a variety of mulch products in bagged quantities. Additionally, mulch is often available for purchase by the tractor scoop or truckload.

The cooler fall weather is a great time of year for the heavy work applying mulch can sometimes be, and your garden will thank you for your efforts with healthier soils and plants.

Due to the shelter-at-home guidelines, the Master Gardeners have canceled all public events for the time being, but their phone lines are still open: 559-684-3325, Tuesdays and Thursdays between 9:30 and 11:30 a.m.

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