9 Ways to Avoid the Worst Mulch Mistakes in Your Garden

I was a new gardener planting my first vegetable patch years ago when a friend gave me hay from his farm to use as mulch. Planting in mulch can really benefit your plants by keeping their roots cooler in hot spells, helping control weeds, and holding moisture in the soil. So I gladly accepted the hay and spread it around my peppers, cucumbers, and tomatoes, then sat back to watch things grow. Things grew all right: plenty of weeds! If only I’d known that I should have composted the hay first to kill the weed seeds in it or chosen a different mulching material, such as shredded leaves. Here’s how you can avoid common mulching mistakes in your garden.

1. Don’t Use Mulch Mixed with Soil

Greg Baka, a long-time gardener and the owner of Easy Digging tools, notes that it’s OK to mix compost into your topsoil to improve it, but let bark mulch lie on the surface of your soil. “Mulch mixed with soil causes difficulties in digging and weeding,” Baka explains. Plus, it can alter nutrient availability and soil structure. Jeff Gibson, landscape business manager for Ball Horticultural Company, adds that you should never use woody mulch as a soil amendment in containers or the ground because “in the process of decaying, it binds up the available nitrogen that could be going to the plants you want to grow.”

Among your veggies, woody mulches like bark chips are not the best choice. “For a vegetable garden, cheap compost does a much better job of mulching than expensive decorative woody mulch. And it feeds the soil,” says Baka. A layer of woody mulch also makes it harder to quickly hoe weeds from between your rows, Baka adds, noting that you must remove it first, weed it, and then put the mulch back.

3. Avoid Fresh Mulches

This was my novice mistake. Mulch materials such as shredded brush, manure, or hay from “pastures, hayfields, or street and highway right-of-ways may contain weed seeds,” Baka says, as well as herbicide residues that can kill your plants. “Let fresh mulch sit a few months to leach out any residue and let weed seeds sprout and die,” he advises. Composting it before use is even better.

4. Watch out for Creeping Plants

Plants that spread by creeping stems, particularly turf grasses such as Bermuda grass, are sometimes so vigorous that they’ll grow right under mulch. Don’t spread mulch on or near these plants if you can avoid it. Instead, Baka recommends keeping them in check with edging that runs above and below the ground, or you can dig a small trench along a bed so you can see runners trying to invade and remove them before they get into the mulch.

5. Get Rid of Weeds Before Mulching

While a good layer of mulch can smother small, young weeds, don’t expect it to magically eliminate well-established weeds. It’s better to remove any big weeds and patches of weeds before mulching over them, or they’ll pop right through. Or, as noted in the previous tip, some may keep on spreading under your mulch.

6. Don’t Use Too Much Mulch

Plant roots need oxygen and water to survive, and a very deep layer of mulch can limit the supply of both. Plus, fungi can become a problem when your mulch layer is too thick, points out Sam Schmitz, grounds supervisor and horticulturist for The Gardens at Ball. “Fungal mats can develop and actually repel the water you are trying to conserve by applying mulch to begin with. One inch of mulch is plenty and more economical.”

7. Prevent Mulch from Touching Your House

When damp mulch touches your siding, it creates a path for termites and other pests to use to get to your home. Baka says it’s OK to use mulch against a concrete wall but keep it at least 6 inches away from wood or wooden structures.

8. Don’t Make Mulch Volcanoes Around Trees

While mulching around trees is a good idea, mounding it up against the trunk is not. That’s because it can keep the tree’s root collar too damp and cause it to rot, warns Gibson from Ball, plus it can encourage insects to bore into the trunk and weaken it. Instead, like keeping mulch from touching your house, leave a little space between your mulch and a tree’s trunk. And don’t pile mulch right up against other plants like shrubs and perennials,either, says Baka. Aim for at least a few inches of space between their stems and any mulch.

9. Avoid Using Dyed Mulch

If you use bagged mulch, Gibson says, “Read the label, as some mulches contain natural dyes, but others may be sprayed-on colorants full of toxins bad for pets and kids. They can leach into the soil and destroy beneficial microbes.” He recommends using composted leaf mulch instead, which looks more natural and improves the soil. “Leaf litter provides overwintering habitat for butterflies and other beneficial insects, too. It’s a natural, renewable resource people bag up and throw out, and then use wood mulch to cover those same beds! Be more Zen in the garden; leave it be. Nature knows what it’s doing.”