How Much Mulch a Bed Needs
Mulch is bought by volume, so the calculation is area multiplied by depth.
Cubic feet = Area (sq ft) × Depth (inches) ÷ 12
Cubic yards = Cubic feet ÷ 27
Bagged mulch is normally sold in 2 cubic foot bags, so one cubic yard is 13.5 bags. Bulk mulch is sold by the cubic yard and delivered loose, which becomes considerably cheaper above about two yards — roughly 27 bags.
How Deep to Spread It
| Depth | Use |
|---|---|
| 1 inch | Refreshing an existing layer, or around delicate seedlings |
| 2 inches | Established beds with a healthy existing layer |
| 3 inches | The standard for new beds — suppresses weeds and holds moisture |
| 4 inches | Heavy weed pressure, or coarse chunky mulch |
| 6+ inches | Pathways only — too deep around plants |
Deeper is not better. More than about 4 inches can starve roots of oxygen, shed water rather than absorb it, and harbour rodents. Fine-textured mulch compacts more than coarse bark, so use the shallower end of the range for it.
Coverage per Cubic Yard
| Depth | Area covered by 1 cubic yard | Bags (2 cu ft) per 100 sq ft |
|---|---|---|
| 1 inch | 324 sq ft | 4.2 |
| 2 inches | 162 sq ft | 8.3 |
| 3 inches | 108 sq ft | 12.5 |
| 4 inches | 81 sq ft | 16.7 |
| 6 inches | 54 sq ft | 25.0 |
Types of Mulch
| Type | Lasts | Notes |
|---|---|---|
| Shredded hardwood bark | 1–2 years | Knits together well, stays put on slopes |
| Pine bark nuggets | 2–3 years | Slow to break down; floats in heavy rain |
| Pine straw | 1 year | Light, acidifying, good for azaleas and blueberries |
| Wood chips | 2–3 years | Often free from tree services; best on paths |
| Compost | Under 1 year | Feeds the soil but suppresses weeds poorly |
| Rubber mulch | 10+ years | Does not decompose, adds nothing to the soil |
| Gravel or stone | Indefinite | Permanent; raises soil temperature |
What Mulch Actually Does
- Suppresses weeds by blocking the light seeds need to germinate. Three inches removes most annual weed pressure.
- Holds moisture by cutting evaporation from the soil surface, often reducing watering by a third.
- Moderates soil temperature, keeping roots cooler in summer and reducing frost heave in winter.
- Improves soil as organic mulches decompose, adding structure and feeding soil life.
- Prevents erosion and stops rain splashing soil-borne disease onto foliage.
Common Mistakes
- Mulch volcanoes. Piling mulch against a tree trunk traps moisture against the bark, invites rot and encourages roots to circle. Keep mulch 3–6 inches clear of trunks and stems.
- Going too deep. Over 4 inches suffocates roots and sheds water.
- Mulching over weeds. Established perennial weeds will push through. Clear them first.
- Plastic sheeting underneath. It blocks air and water exchange. Landscape fabric is better but still degrades soil health over time; a thick mulch layer alone usually works better.
- Fresh wood chips dug into soil. Decomposing wood ties up nitrogen. On the surface this is not a problem; mixed into the soil it is.
When to Mulch
Mid to late spring, once the soil has warmed — mulching too early keeps the ground cold and slows growth. A second light application in autumn protects roots over winter. Refresh annually as organic mulch decomposes; you will usually be topping up by an inch rather than replacing the whole layer.
Frequently Asked Questions
How many bags in a cubic yard?
13.5 bags of 2 cubic feet each. Some brands sell 1.5 or 3 cubic foot bags, so check the label before dividing.
How much does a cubic yard of mulch weigh?
Roughly 400–800 lb dry, depending on type, and considerably more when wet. Most pickup trucks handle one to two yards safely; check your payload rating.
Is bulk cheaper than bagged?
Usually, above about two cubic yards. Below that, delivery charges wipe out the saving.
Do I need to remove the old mulch first?
Not normally. Rake it to break up any crust and top up to the target depth. Remove it only if it has matted into a water-repellent layer or shows signs of disease.