Lay mulch in layers 2 to 4 inches deep, spreading it evenly across the soil around plants and trees, keeping it a few inches away from tree trunks and plant stems to prevent rot

Mulch works best when it sits at the right depth and stays in the right places. Too shallow and it won't suppress weeds or retain moisture; too deep and it can trap water against plant stems and cause them to rot. The standard depth is 2 to 4 inches, measured from the soil surface. You spread it across the entire bed, but always leave a 3- to 6-inch gap around the base of trees and the crown of shrubs and perennials—the point where the stem meets the soil.

The actual work is straightforward: clear the bed, measure your material, and spread it evenly. Most people finish a typical garden bed in an hour or two. The hardest part is usually getting the mulch to the site and calculating how much you need.

Key Takeaways

  • Mulch should be 2 to 4 inches deep across the entire bed, but kept 3 to 6 inches away from tree trunks and plant stems.
  • Remove weeds, dead leaves, and debris from the bed before you spread mulch, so you are not burying problems.
  • Calculate the volume you need by multiplying the bed's length by width by depth (in feet), then divide by 27 to get cubic yards.
  • Spread mulch by hand or with a shovel, working from the edges inward, and rake it level so water can soak in evenly.
  • Refresh mulch every year or two as it breaks down, but do not add new layers on top of old ones without removing some first.

Prepare the bed before spreading mulch

Start by clearing the bed of weeds, fallen leaves, dead plant material, and any debris. Mulch will not kill existing weeds—it will bury them and make them harder to pull later. If you have a serious weed problem, pull or dig out the worst offenders first. For small weeds, you can pull them as you go, but the cleaner the bed, the better the mulch will work.

Check the soil level and grade. If the bed has low spots where water pools, fill them in or rake the soil level. Mulch will settle over time, so a slight slope away from trees and structures helps water drain. You do not need to add anything to the soil itself—mulch sits on top and works its way down naturally as it breaks down.

Calculate how much mulch you need

Measure the length and width of your bed in feet. Multiply those two numbers together to get the square footage. Then multiply by the depth you want in inches—let's say 3 inches as a middle ground. Divide that result by 324 (a constant that converts cubic inches to cubic yards). The answer is how many cubic yards of mulch to order.

Example: a bed that is 10 feet long, 4 feet wide, and you want 3 inches deep. (10 × 4 × 3) ÷ 324 = 0.37 cubic yards. You would order 1 cubic yard to have a little extra. If your bed is irregular, break it into rectangles, calculate each one, and add them together. Most mulch suppliers sell by the cubic yard, and a cubic yard covers roughly 100 square feet at 3 inches deep.

Spread mulch evenly across the bed

Dump the mulch in piles around the bed—not all in one spot, or you will spend hours moving it. Start at one edge and work toward the center, using a shovel or your hands to spread it. Aim for an even depth across the whole bed. A garden rake helps you level it and break up any clumps. The goal is a uniform layer that looks neat and lets water soak in evenly.

As you spread, keep the mulch a few inches away from tree trunks and the stems of shrubs and perennials. Mulch piled against wood or soft plant tissue traps moisture and can cause rot, pest damage, and disease. If you have a tree with roots that flare out at the base, keep mulch away from the entire flared section. A 3- to 6-inch gap is standard; err on the side of more space rather than less.

Water the bed after mulching

Once the mulch is in place, water the bed thoroughly. This settles the mulch, helps it make contact with the soil, and ensures moisture reaches the plants underneath. If the mulch floats or shifts, rake it level again and water once more. The mulch will compress slightly over the first few weeks as it settles and begins to break down.

After that, water as you normally would. Mulch slows evaporation, so you may need to water less often than before, but the soil underneath still needs to stay moist for your plants. Check the soil under the mulch by pulling it back slightly—if the soil is dry an inch or two down, water.

Refresh mulch as it breaks down

Mulch breaks down over time as microorganisms decompose it and weather breaks it apart. After a year or two, you will notice it looks thinner, darker, and more like soil than wood chips or bark. At that point, it is time to refresh it. Do not straightforward add a new 3-inch layer on top of the old one—that can build up to 6 or 8 inches, which is too deep and can smother plants.

Instead, rake back the old mulch, remove about half of it (or all of it if it has mostly turned to soil), and spread fresh mulch to bring the depth back to 2 to 4 inches. This keeps the layer at the right depth and lets you see what is happening at the base of your plants. If you see rot, pest damage, or disease, you can address it before it spreads.

Mulch around trees and shrubs

Trees and shrubs need the same mulch depth as garden beds—2 to 4 inches—but the spacing rule is even more important. Create a mulch ring around the tree or shrub, keeping the mulch at least 3 to 6 inches away from the trunk or main stems. The ring should extend out to the drip line (the outer edge of the canopy) if possible, or at least 2 to 3 feet from the trunk for young trees.

For trees with exposed root flares—where the roots spread out at the base—keep mulch away from the entire flared area. Mulch against the flare can cause the bark to rot and create entry points for pests and disease. If you have an older tree with mulch piled against the trunk, pull it back now. You may see some damage, but removing the mulch will stop further harm.

Frequently Asked Questions

Can I lay mulch directly on top of old mulch?

Not as a regular practice. If the old mulch is still recognizable as wood chips or bark and sits at a reasonable depth, you can add 1 to 2 inches of fresh mulch on top. But if the old layer has mostly broken down into soil-like material or is already 4 inches deep, remove some of it first. Layers thicker than 4 inches can trap moisture and harm plants.

What is the best time of year to lay mulch?

Spring and fall are ideal because the soil is moist and plants are actively growing. You can mulch in summer, but water the bed well first and watch it closely during hot spells—mulch can dry out quickly if the soil underneath is already dry. Avoid mulching in late fall if you live where rodents nest in mulch; wait until spring instead.

Should I use landscape fabric under the mulch?

Landscape fabric can slow weed growth, but it also slows water and air penetration into the soil. If you use it, choose a permeable type and overlap the seams by 6 inches. Many gardeners skip it and straightforward pull weeds as they appear—it is faster than dealing with fabric that tears and shifts. Cardboard under mulch works better than plastic fabric because it breaks down over time.

How do I keep mulch from washing away on a slope?

On a slope, use a slightly deeper layer—3 to 4 inches instead of 2 to 3—and consider using larger wood chips or bark nuggets, which are heavier than fine mulch. You can also install a shallow border or edging at the downhill side of the bed to hold mulch in place. Water gently rather than with a strong spray, which can wash mulch downhill.

Can I use fresh wood chips from a tree service?

Yes, but let them sit for a few weeks first. Fresh chips heat up as they decompose and can kill plants if spread while hot. Pile them in a corner, let them cool, and use them once they smell earthy rather than hot or sour. Fresh chips also break down faster than aged mulch, so you may need to refresh them sooner.