7 mulching mistakes to avoid
Mulch is one of the cheapest ways to improve a garden — and one of the easiest to get wrong. These are the mistakes extension horticulturists see most often.
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1. Piling mulch against the trunk
"Volcano mulching" — mounding mulch up the trunk of a tree — is one of the most common causes of tree decline. Mulch against the bark keeps it wet, which invites rot, insects and disease, and can encourage roots to circle the trunk. University of Illinois Extension recommends keeping mulch at least 4 inches away from the trunk. Think of a donut, not a volcano.
2. Going too deep
The recommended depth is 2 to 4 inches: 2 to 3 inches for fine or composted mulch and 3 to 4 inches for coarse wood chips and bark. Thicker layers can mat down, keep water and oxygen from reaching roots and keep the soil too wet. Adding a fresh 3 inches every spring on top of last year's mulch is how beds end up 8 inches deep.
3. Buying without measuring the existing layer
Before you order, push a finger or trowel into the bed. If there's still 2 inches of mulch, you only need a top-up of an inch or two — or just a rake to fluff up and refresh the color. Enter only the depth you're adding in the mulch calculator; it often halves the order.
4. Putting landscape fabric under wood mulch
Fabric under organic mulch looks tidy at first, but as the mulch breaks down it forms a layer of compost on top of the fabric, and weeds root straight into it. The fabric also keeps that organic matter from improving the soil. Fabric works better under gravel and stone than under wood mulch.
5. Mulching over weeds and dry soil
Mulch suppresses new weed seeds; it doesn't reliably smother established perennial weeds. Pull or dig them first. Water dry beds before mulching, too — a thick layer over dry soil can shed light rain for a while.
6. Worrying too much about nitrogen
A common belief is that wood chip mulch "steals" nitrogen from plants. Soil microbes do use nitrogen as they break wood down, but with mulch left on the surface this happens mainly in the thin layer where mulch meets soil, and it has little effect on established plants. The problem is real when fresh wood chips are mixed into the soil, so don't dig them in when planting.
7. Using the wrong amount for the shape
Curved beds are hard to estimate by eye, and it's easy to over- or under-order by a third. Measure them properly — see how to measure an irregular area — and remember that bulk mulch is sold by the cubic yard, bags usually by 2 or 3 cubic feet.
How much mulch to buy
| Bed area | At 2 in | At 3 in |
|---|---|---|
| 50 sq ft | 0.31 yd³ · 5 bags (2 cu ft) | 0.46 yd³ · 7 bags |
| 100 sq ft | 0.62 yd³ · 9 bags | 0.93 yd³ · 13 bags |
| 200 sq ft | 1.23 yd³ · 17 bags | 1.85 yd³ · 25 bags |
| 500 sq ft | 3.09 yd³ · 42 bags | 4.63 yd³ · 63 bags |
Before any extra allowance. Past a couple of cubic yards, bulk delivery is usually cheaper than bags.
Sources
- University of Illinois Extension, Proper mulching techniques — recommended depths and distance from trunks.