How to Mulch Landscape Beds: Depth, Materials, Edging and Bags

Multiply bed area in square feet by depth in inches and divide by 324 to get cubic yards. A 200 square foot bed at 3 inches needs about 1.85 cubic yards, or 25 bags of 2 cubic feet. Buy 5 to 10 percent extra for uneven beds and settling. For circles, area is 3.1416 times the radius squared, so a tree ring with a 3 foot radius is about 28 square feet.

Bags make sense for small jobs, touch-ups and yards with no place for a delivery pile: they are clean to haul, easy to count, store well and let you buy exactly what you need. Bulk mulch is usually cheaper per cubic yard once a job reaches a few yards, especially with local delivery, and it is the only practical way to cover large beds. Compare the delivered price per cubic yard against 13.5 bags of 2 cubic feet at your store's price.

• Bulk tips: have it dumped on a tarp on the driveway or lawn close to the beds, spread it within a few days, and ask the supplier what the material is made of. Quality and color vary by supplier.
• Weight: dry shredded wood mulch is commonly 400 to 800 pounds per cubic yard, and wet mulch weighs much more, which matters for cart capacity and your back.
• Bag tips: check that bags are not heavy and soggy or smelling sour, which can mean anaerobic material that can harm plants; air it out before spreading if so.

Mulch prevents new weeds from sprouting by blocking light, but it does not kill established weeds, which grow right through. Before spreading:

• Pull or dig existing weeds with roots, especially perennials like bindweed and quackgrass. Spot treating weeds is covered in the weed killer safety guide; follow the label exactly and never spray near desirable plants on a windy day.
• Rake out excess old mulch if total depth would exceed about 3 inches, or fluff matted old mulch so water can penetrate.
• Cut or refresh the edge (next section) so mulch stays out of the lawn.
• Water the soil if it is dry, because mulch holds existing moisture in and a dry bed under fresh mulch can stay dry.
• Skip landscape fabric under organic mulch in planting beds. Extension services commonly note that as organic mulch breaks down on top of fabric, weeds root into it, and fabric blocks organic matter from reaching the soil. Woven fabric like the DeWitt Pro-5 Weed Barrier Fabric (6 x 250 ft.) is better suited under stone and gravel paths. A layer of plain cardboard or newspaper under organic mulch is a common alternative that smothers weeds and breaks down.

A clean edge keeps mulch in the bed and grass out of it. Choose one method:

• Spade-cut edge: cut a V-shaped trench a few inches deep along the bed line, with the vertical side against the lawn, and throw the soil into the bed. A sharp spade like the Radius Garden Pro-Lite Carbon Steel Spade does it by hand; it needs recutting once or twice a season.
• Power edger: a battery edger such as the EGO Power+ ME0820 8 in. Edger with Multi-Head Power Head (tool only) or corded WORX WG896 12 Amp 7.5 in. Corded Electric Edger and Trencher recuts long edges in minutes. See the best lawn edgers.
• No-dig plastic edging: the EasyFlex Heavy Duty No-Dig Edging Kit (100 ft.) forms curves and tree rings with anchoring spikes and no trenching, for a budget physical barrier.
• Steel edging: hammer-in COR-TEN steel like the Edge Right Hammer-In COR-TEN Steel Edging (5 x 48 in.) reaches 6 inches deep, holds crisp lines and weathers to a rust patina that resists string trimmer hits.

Physical edging and trenched edges compare in the best landscape edging.

Trees and shrubs: pull mulch back 3 to 6 inches from trunks and stems, and spread it 2 to 3 inches deep in a wide, flat ring, ideally out toward the drip line. Mulch piled against a trunk, often called a mulch volcano, holds moisture against the bark, which invites rot, disease, insects and rodents that chew bark, and can encourage roots to grow up into the mulch and circle the trunk. University extension arborists consistently warn against it.

Houses: keep mulch and soil well below wood siding and trim. Model residential building codes treat about 6 inches of clearance between the ground and untreated wood siding as the benchmark, and brick homes need weep holes left uncovered. Organic mulch against the foundation holds moisture where termites and carpenter ants find it, so many pest guides suggest a narrow mulch-free or stone strip right at the wall. In wildfire-prone areas, Firewise USA guidance is to keep the first 5 feet around the house free of combustible mulch.

Also keep mulch off the crowns of perennials and away from air conditioner condensers, dryer vents and utility boxes.

Mulch is bulky and heavy when wet, and the fork and cart matter more than muscle. Trips per cubic yard assume the container is filled level; lighten loads of wet mulch to stay within the cart's weight rating.

A multi-tine fork, not a shovel, is the right loading tool for loose mulch: the Truper TruTough 10-Tine Ensilage Fork has the tine spacing used for mulch, compost and bedding, and it slides into a pile far easier than a flat blade. Spread and level with a steel bow rake such as the Bully Tools 16 in. Bow Rake, flipping it tines-up to smooth the surface. For bagged mulch, lay bags out across the bed before opening them to spread evenly, slit them lengthwise and pull the bag out from under the pile.

Wear gloves, since bark and hardwood carry splinters, and a dust mask when spreading dry, dusty material. Lift bags with your legs and use the cart to carry them rather than walking them across the yard.

Mid to late spring, once the soil has warmed and after spring weeding, is the most common time, because mulch applied to cold, wet soil keeps it cold and slows early growth. A late summer or fall application helps insulate roots of new plantings through winter, and in cold climates a winter mulch goes on after the ground begins to freeze. Mulch new plantings right after planting in any season. Avoid spreading pre-emergent or fresh mulch right before heavy rain on slopes, when it can wash away.