Got Mulch? The Complete Guide to Choosing & Applying Garden Mulch

No matter where you live, your garden benefits year-round from properly applied mulch: a layer of organic or inorganic material spread evenly on the soil surface. Today's gardeners have many mulch choices, but deciding which to use takes research.

(Editor's Note: Originally published April 7, 2008. Comments welcome, but authors may not promptly respond.)

More Than Just Pretty

A carefully designed landscape instantly becomes a pièce de résistance with decorative mulch. Varying shades and textures artistically contrast garden shapes and colors—imagination is the only limit. But mulch has greater benefits, two critically important:

• Conservation of soil moisture
• Stabilization of soil temperature

1969 Weyerhauser research proved 2" bark mulch:

• Reduced summer moisture evaporation by 21%
• Reduced summer soil temperature (upper 4 inches) by 10°F
• Delayed soil freezing by two days (vs. unmulched)

Additional Benefits

• Prevents weed growth
• Reduces heaving in small plants (roots forced up by freeze-thaw cycles)
• Organic mulch adds organic matter via decomposition
• Reduces soil erosion
• Prevents disease by keeping leaves, fruits, vegetables, flowers off soil

What Kind Should You Use?

Mulch falls into two categories: organic (plant/animal materials that break down) and inorganic (natural/artificial materials that don't decompose or decompose slowly).

Organic Mulch Advantages

• Increases soil aeration (especially clay)
• Increases water retention in sandy loam
• Improves/stabilizes soil structure against rain impact, compaction
• Increases cultivation ease
• Releases major/minor mineral elements (not a fertilizer substitute)
• Can change soil pH

Cost, longevity, appearance drive choices. Small gardens: cost less critical. Large areas: prioritize criteria. Slow-decomposing mulches improve soil slowly but need less replacement. Poor soil: choose shorter-lived mulch for faster improvement. Large areas needing coverage for water retention/weed control: use less expensive general mulch vs. decorative (pine nuggets, dyed mulches).

Mulch Types & Features (from Ohio State University Extension)

Organic: Traditional Bark Mulch

• Pine bark & nuggets: Long-lasting, slow decomposition, excellent weed control
• Cypress: Medium-long lasting, excellent weed control; may cause nitrogen deficiency
• Shredded hardwood: Medium-long lasting, excellent weed control; may cause slight nitrogen deficiency

Organic: Recycled Products

• Composted yard wastes: Medium lasting, good soil improvement; fine grind for soil prep, coarse for mulching; useful on poor topsoil
• Composted leaves: Short-lasting, better as soil amendment; useful for seed/planting beds
• Ground & dyed wood pallets: Medium lasting, good for paths/picnic areas; causes nitrogen deficiency, especially annuals/perennials; dye effects questioned
• Wood chips: Medium lasting, for established plantings/trees; causes nitrogen deficiency if not composted first; "green mulch" can get hot and damage plants
• Animal manures: Short lasting; commercially packaged cow, horse, sheep, poultry, zoo waste; amending, mulching, fertilizing; weed seeds sometimes introduced
• Composted municipal sludge: Short lasting; may include garbage, paper pulp, yard waste; brands: Earthlife®, Comtil®, TechnaGro®
• Sphagnum peat moss: Long lasting; from long-fiber mosses resisting decomposition; primarily soil amendment
• Pine needles: Medium lasting; excellent for evergreens and acid-loving plants
• Straw/Hay: Short lasting; winter protection for perennials, strawberries, small plants, new turfgrass; blows away; weed seeds often introduced

Organic: Blends

• Typically finely ground compost + coarse products (bark, dyed wood mulches)

Inorganic Mulches

• Stone, gravel, lava rock, pebbles: Very long lasting; fire resistant; resist blowing/washing; use with underlying plastic/fabric for weed control; light colors radiate heat, overheat plants; debris cleanup difficult; no soil benefit; limestone raises pH detrimentally
• Ground/shredded tires: Very long lasting; ideal for playgrounds; not for home landscape
• Landscape fabric: Medium lasting (UV oxidation); excellent weed barrier; porous, allows water penetration
• Black polyethylene: Long lasting; some vegetable/vine crop use; not recommended for landscape—soil stays too wet unless well drained
• Aluminum foil: Long lasting; mostly vegetable gardens—significantly reduces insect pests/viruses

Other Mulch Materials

• Newspaper: Short lasting (one season); excellent weed barrier, retains moisture; good between vegetable rows
• Grass clippings: Short lasting; excellent short-term nutrient-rich mulch that amends soil; unpleasant odor as decomposition begins in warm weather
• Cocoa hulls: Long lasting; adds nitrogen; good weed control; high cost; absorbs heat; may develop mold
• Peanut shells: Short lasting; adds nitrogen; good water retention/weed control; low-moderate cost
• Buckwheat hulls: Long lasting; good weed control; may sprout; high cost; blows in wind

Not Foolproof

"Bargain" mulches bring grief. Weed seeds and fungi thrive in the "perfect incubator." Thistle (Cirsium spp.) and Mugwort (Artemisia princeps)—tenacious invasives with frightening adaptive powers—often lurk in bulk mulch. Once imported, you'll battle them long-term. Nuisance/detrimental molds and fungi appear in mulches with perfect temperature, pH, moisture.

• Shotgun/artillery fungus (Sphaerobolus): Tiny "cups" filled with spores (like black eggs). Shoots spores into air—they stick everywhere, staining siding, furniture, plant leaves.
• Slime molds: Slimy yellow/orange masses; produce toadstools, some toxic to humans.
• Too-deep mulch (3–6+ inches): Underlying layers undergo high-temp summer decomposition. Mulch dries below 34% moisture → dusty mass inviting fungi. Becomes moldy, hard, water runs off → drought beneath.
• Diseased-tree mulch: May harbor pathogens like Verticillium dahliae (wilts, death of shade trees/shrubs) or Rhizoctonia solani (damping-off of seedlings, stimulated by fresh mulch).

Best control: purchase composted products low in wood content (Harry A.J. Hoitink, OSU Extension).

How Much is Enough?

Recommended depth: 2–2½ inches for weed control, water retention, temperature stabilization. Large-piece mulches (giant nuggets) cover less area—better for decorative use with underlying landscape fabric.

Biggest homeowner mistake: 3–6+ inches. Heavy layer drastically reduces soil's ability to dry out → soggy, waterlogged roots. Extremely damaging to azaleas, rhododendrons, most conifers, all Taxus (yew), many perennials.

Mulch piled against stems/trunks → constantly wet bark → perfect disease conditions. Rodents nest in thick mulch, feed on softened wood in winter scarcity.

Coverage Calculations

• 2" depth: 2 cu ft covers 12 sq ft; 3 cu ft covers 18 sq ft
• Bulk: 1 cu yd covers 162 sq ft at 2"
• Small pickup: ~1.5 cu yd (243 sq ft); full-size: ≥2.5 cu yd (405 sq ft)

Timing is Everything

When soil has warmed and begun to dry, plan mulching. Don't mulch too early—material keeps soil from drying. Plants begin root growth as oxygen becomes available and soil warms in root zone. Cold regions/heavy spring rain: delay until May/June.

Long, hard winters: second application in autumn, especially on new plants with shallow roots (shrubs, evergreens, herbaceous perennials, strawberries). Water established plants thoroughly late fall, then mulch. Reduce heaving on new/small plants: mulch immediately after first ground frost.

Mulch is your best garden helper if you use the right material and follow accepted guidelines.