Winter Mulch for Perennials: When to Put It Down and How Much

Put winter mulch on perennials after the ground freezes, not before. Iowa State University Extension recommends about 4 inches of mulch over the crowns, and 6 to 8 inches of straw, pine needles or chopped corn stalks for tender perennials. Mulching too early can delay dormancy.

Free calculator: enter your bed size and a 4 in depth in our free mulch calculator to get bags and cubic yards, with bag and bulk prices side by side. No sign-up.

When to put winter mulch down

Wait for frozen ground. Iowa State says to mulch after the ground freezes, typically by late November in much of Iowa. Colder or warmer areas shift that date.

Cut back after a hard freeze. Perennials can be cut back once a hard freeze has killed the foliage. You don't have to clear the whole garden after the first frost.

Why it matters. Freeze and thaw cycles can push crowns and roots out of the soil, called frost heaving. Iowa State notes that leaving plant debris in place over winter can help shallow-rooted perennials that may heave.

How much winter mulch you need

Counts are 2 cu ft bags, rounded up.

4 in deep, most perennials — 50 sq ft: 16.7 cu ft, 9 bags; 100 sq ft: 33.3 cu ft, 17 bags (1.23 cu yd); 200 sq ft: 66.7 cu ft, 34 bags (2.47 cu yd)

6 in deep, tender perennials — 100 sq ft: 50 cu ft, 25 bags (1.85 cu yd)

8 in deep, tender perennials — 100 sq ft: 66.7 cu ft, 34 bags (2.47 cu yd)

Other bed sizes and bag sizes: use the free mulch calculator. Shredded leaves cost nothing: see how to turn fall leaves into free mulch.

Take it off in spring

Pull the extra mulch back in early spring, as soon as the top layer of soil thaws. That is usually around mid-March in most of Iowa (Iowa State); adjust for your area. Vegetable beds need winter cover too: see how to get raised beds ready for winter.

Tools for winter mulching (#ad)

WORX WG430 Leaf Mulcher — a stand-alone shredder that the maker says handles up to 53 gallons of leaves a minute at an 11:1 ratio. It empties into a bag you attach underneath (bag not included). See it on Amazon

Gorilla Carts 4 Cu Ft Dump Cart — the maker rates it for 600 lb, with a quick-release dump bed and 10-inch pneumatic tires. One 4 cu ft load covers 12 sq ft at 4 in deep, so a 100 sq ft bed takes about 9 loads. See it on Amazon

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Winter mulch FAQ

When should I put winter mulch on perennials? After the ground freezes, typically by late November in much of Iowa, per Iowa State University Extension. Mulching too early can delay dormancy.

How thick should winter mulch be? About 4 inches over the crowns, and 6 to 8 inches for tender perennials (Iowa State).

What makes good winter mulch? Iowa State lists straw, pine needles and chopped corn stalks for tender perennials. NC State Extension lists straw (not hay), pine needles or chopped leaves for raised beds.

How many bags of mulch for 100 sq ft at 4 inches? 33.3 cu ft: 17 bags of 2 cu ft, or 1.23 cubic yards.

When do I take winter mulch off? In early spring, as soon as the top layer of soil thaws.

Sources: Iowa State University Extension and Outreach, How should I prepare my perennial beds for winter?; NC State Extension, Winterizing Your Raised Garden Beds.