What is mulch? Choosing the right cover for your garden beds

Mulch is the layer of material spread over the soil in a garden bed or planting area. Bark and wood chips are familiar examples, but compost, leaves and decorative rock can serve as mulch, too. The right choice depends on what is growing there, how the space is used and the look you want.

For Southwest Washington homeowners, mulch can help protect bare soil through rainy weather and reduce moisture loss during summer. It can also make weeding easier. The important part is choosing the material and depth for the bed, rather than simply covering every open spot with the same product.

Bark and wood chips: practical choices for planted beds

Bark and wood mulch give shrub beds a finished appearance while covering exposed soil. They gradually break down, so you will eventually need to refresh them. Keep these materials on the surface rather than mixing fresh bark or chips into the planting soil, where decomposition can temporarily tie up nitrogen that plants need.

Dark hemlock has a finer texture and a subdued color that lets plants stand out. Shovel & Thumb’s product is screened hemlock bark. It is a useful option when you want a fairly even-looking finish around shrubs and garden beds.

Nugget bark has more visible, chunky pieces. Larger bark pieces generally break down more slowly and resist packing better than fine bark, making them worth considering when longevity matters more than a fine-textured appearance.

Cedar chips offer a coarser wood-chip texture. Compare a sample with bark before choosing; particle size and appearance make a noticeable difference once a whole bed is covered. Choose them for the landscape job they need to do, rather than relying on mulch as a pest-control treatment.

Rock mulch: long-lasting, with different trade-offs

Decorative stone, including river rock, can provide a durable surface around selected plantings. It does not decompose like bark, and it works well where the design calls for a distinct stone texture.

Stone can also make the soil hotter in summer, so consider the plants and exposure before using it across a bed. Leaves and soil still collect between the stones, and weeds can establish in that debris. Long-lasting does not mean maintenance-free.

Where wildfire exposure is a concern, noncombustible material near structures deserves special consideration. A stone-covered area can serve a different purpose from the organic mulch used farther out in planted beds.

Compost, topsoil and mulch are not interchangeable

Compost is decomposed organic material. It can improve soil when used as an amendment, and it can also be spread on the surface as mulch. Its finer texture makes it useful in some flower and vegetable beds, although it is not as dependable a weed-suppressing cover as coarse woody mulch.

Topsoil supplies soil volume for the appropriate planting or grading job. It is not a substitute for a weed-suppressing mulch layer. Likewise, a planting-soil blend and a surface mulch are doing different jobs. If you are building a new bed, work out what the plants will grow in before choosing what will cover the surface.

Apply enough, but do not bury the plants

Start by removing weeds and checking how much old mulch remains. For established tree and shrub beds, Oregon State University recommends about 3 inches of bark, or 3 to 4 inches of coarser wood chips. Fine bark needs particular care: keep it to roughly 2 to 3 inches rather than piling it thickly.

Those depths describe the total layer, including mulch already there. Pull it away from trunks and plant bases, and keep perennial crowns uncovered. If the bed stays wet, use less and address the drainage problem instead of adding a heavy blanket. Check beneath the mulch after watering to make sure moisture is reaching the soil.

Measure before ordering

For a rectangular bed, multiply its length by its width to find the square footage. Then multiply by the mulch depth in inches and divide by 324 to estimate cubic yards. A 100-square-foot bed covered 3 inches deep needs about 0.93 cubic yard.

Measure irregular beds in smaller sections and add them together. Shovel & Thumb’s bulk product pages include a yardage calculator, so you can check the quantity before choosing pickup or delivery.

Refresh the bed when it needs it

Spring is a useful time to check mulch before summer drying begins. Fall can also be a good opportunity to cover bare ground. You do not need to add a full new layer every year: check the depth, loosen any packed surface and top up only where needed.

A good mulch choice should suit the plants, the site and the amount of upkeep you want. Start with those three things, and the color and texture are much easier to choose.