When examining your garden beds and borders, you might notice some areas with bare soil. This signals the need for mulch, which serves as a protective layer on the soil. Mulch retains moisture, suppresses weed growth, and regulates soil temperature around plants. However, incorrect use can cause more harm than benefit.

The Right Kind of Mulch

Mulch options range from gravel, plastic sheeting, and shredded tires to organic materials such as compost, pine needles, shredded bark, hay, straw, and wood chips. Each has a different impact on plants.

Gravel and stones can reduce weeds and retain some moisture, but they affect plants differently than organic mulch. Stones absorb heat, which might scorch plants and roots. Additionally, removing gravel later can be challenging. In fire-prone areas, gravel is recommended since organic mulches are flammable.

Avoid using shredded tires. Crumb rubber carries volatile organic compounds and heavy metals like lead. Even if removed, chemical residues can linger indefinitely unless you replace soil layers.

The benefits of plastic sheeting are overshadowed by disposal issues. It eventually breaks into microplastics, contaminating soil and water. Natural materials like shredded bark, wood chips, straw, and pine needles are preferable as they enrich the soil upon decomposition.

Choosing the Best Natural Mulch

Arborist wood chips, derived from tree pruning, are highly recommended. They decompose into rich humus on the soil surface, nourishing plants. As most of the chips come from the inner wood, they retain and release moisture more effectively.

Shredded bark mulch is another option. While it performs similar functions to wood chips, it is less effective at moisture retention. It is also lightweight, making it prone to displacement by rain or leaf blowers.

Avoid dyed mulches due to potential toxicity. Even if high-quality, the wood used might come from questionable sources, such as construction debris. Dyed mulches are particularly unsafe for food crops.

Mulching Tips

For best results, mulch around plants with a 3- to 4-inch layer. Keep it a few inches away from trunks and stems to promote airflow. Direct contact traps moisture and encourages rot.

Avoid piling mulch against tree trunks, a practice called “volcano mulching,” as it suffocates trees, leading to decay and eventual death. Correct mulching exposes the trunk’s base flare for visibility.

Apply mulch after the risk of frost has subsided but before weeds appear. Early application can trap cool temperatures, delaying plant growth. Late application can lead to soil erosion, increased weed growth, and moisture loss. Moreover, mulch can enhance the garden’s aesthetic appeal.

Jessica Damiano writes regular gardening columns for The Associated Press. She publishes the award-winning Weekly Dirt Newsletter.

For additional gardening tips, visit AP Gardening.