How Much Winter Mulch Do You Need? Depth and Bag Math
Square feet times depth in inches, divided by 12, gives cubic feet. A 4 by 8 foot bed at 4 inches needs about 10.7 cubic feet. Depths by plant from extens...
Published by ThriveThyme
mulch winter calculator
How Much Winter Mulch Do You Need
Multiply the bed's length by its width in feet to get square feet. Multiply by the depth in inches and divide by 12. That is cubic feet. Divide cubic feet by 27 for cubic yards.
A 4 by 8 foot bed at 4 inches deep is 32 square feet times 4, divided by 12, or about 10.7 cubic feet. That is 6 bags of 2 cubic feet, or 4 bags of 3 cubic feet.
The Winter Mulch Desk does this for every bed at once and fills in the depth for each plant type.
Depth by Plant
| Plant | Depth | Source |
|---|---|---|
| Perennial flowers | About 4 in over crowns. Minnesota says 5 to 6 in | Iowa State, Minnesota |
| New or borderline hardy perennials | 6 to 8 in of straw or pine needles in a cage | Iowa State |
| Strawberries | 4 to 6 in of loose straw | Minnesota, West Virginia |
| Garlic | 3 to 4 in of straw or leaves | Minnesota |
| Spring bulbs | 5 or 6 in | Minnesota |
| Carrots and parsnips left in the ground | 6 to 8 in to dig into winter, a foot or more for all winter | Illinois, New Hampshire, UC ANR |
| New trees and shrubs | 3 to 4 in of shredded wood, never over 4 in | Minnesota, Virginia |
Quick Table
Cubic feet for a 10 square foot area at each depth. Scale it up for your bed.
| Depth | Cubic feet per 10 sq ft |
|---|---|
| 2 in | 1.7 |
| 3 in | 2.5 |
| 4 in | 3.3 |
| 6 in | 5 |
| 8 in | 6.7 |
| 12 in | 10 |
Roses Are Counted Per Plant
Grafted roses get a mound of soil 10 to 12 inches high over the base (Iowa State, New Hampshire, Nebraska). Purdue says a 12 inch mound takes about 5 gallons of soil per rose. That is about 0.7 cubic feet each, so 10 roses need about 6.7 cubic feet of soil. Bring the soil in from another spot. Do not dig it from around the roses. See how to protect roses in winter.
Using Bags of Leaves
A 39 gallon lawn bag holds about 5.2 cubic feet of loose leaves. Shredded leaves pack down, so plan on more bags than the math says. Shred them first so they do not mat over crowns. See how to shred leaves for garden mulch and the Fall Leaves Desk.
Iowa State warns that whole leaves often pack down and smother tender perennials. For those plants, use loose straw or pine needles.
Buying Tips
- Bags are usually 2 or 3 cubic feet. Read the label.
- Bulk mulch is sold by the cubic yard. One cubic yard is 27 cubic feet.
- Use clean, weed free straw, not hay. Hay carries weed seed (Minnesota).
- Fluffed straw and loose leaves settle, so gather a little extra.
Next Steps
- Add your beds on the Winter Mulch Desk and download the plan as a CSV.
- Learn when to apply winter mulch so it goes on at the right time.
Sources
- Iowa State University Extension, How should I prepare my perennial beds for winter?
- Iowa State University Extension, How to Overwinter Plants
- University of Minnesota Extension, Mulch perennials and bulbs after the soil freezes
- University of Minnesota Extension, Growing strawberries in the home garden
- University of Minnesota Extension, Growing garlic in home gardens
- University of Minnesota Extension, Protecting trees and shrubs in winter
- Purdue University Consumer Horticulture, Hibernation for Roses
- University of Illinois Extension, Late Season Vegetable Storage Tips
- University of California ANR, Storing Vegetables and Fruits at Home
- Virginia Cooperative Extension SPES-661, Mulching