Winter Mulch - DIG IT! Magazine

If you haven’t done so yet, now is the time to mulch your garden.

We know that mulch helps prevent soil compaction, protect against soil erosion, keep weeds at bay, reduce water loss, maintain even soil temperatures and improve the landscape’s look. When we use mulch in our gardens we usually spread it over the soil at the beginning of the growing season and reapply it around new plantings, but what about the winter months? If you cherish your bulbs and plants you should also apply mulch during the winter.

Non-organic mulches usually last longer and they have their place. If you are working on a new bed and want to kill grass, place black polyethylene film over the area. It will kill the grass by excluding light.

Organic mulches will decompose and have to be replaced; however, in the process they improve your soil’s fertility and organic content and may alter the pH of your soil. When pine needles and oak leaves decompose they lower the pH of the soil, making it more acidic which is beneficial to ericaceous plants such as azaleas and rhododendron. On the contrary maple leaves, especially Norway maple, and elm leaves may leave you with a soil more suited for a variety of alkaline plants such as pinks and bellflower.

Leaves are nature’s omni-present mulch and should be used wherever possible. In the forest leaves protect roots and add nutrients to the soil as they decay. By using leaf mulch you imitate Mother Nature’s natural process. Shredded and partially decomposed leaves are best. Non-shredded leaves lie flat, packed down and seal the surface, not allowing air and water in. Shredded leaves decompose faster and are less likely to be blown around by wind. All deciduous leaves may be used, though some, such as hornbeam, beech, and oak, break down quicker than others. Use a shredder or run the leaves over with a lawn mower several times.

Tree bark has value as mulch, but should be shredded or broken up into chips before use. Generally the drier and woodier the mulch, the slower it will decompose. Wood chips usually last at least 2 years. During the decaying process microbes tie up soil nitrogen so it is advisable to add a generous application of nitrogen-carrying fertilizers just prior to spreading wood chips.

Untreated grass clippings can be used as mulch but if applied too thick can heat up and become a dense mat, not allowing air and water to pass through. Let grass clippings dry before putting them around your garden and then apply loosely.

Straw is good winter mulch because it is loose material, allowing air filtration. Hay is bulky to put down, doesn’t look attractive, harbors mice and brings weed seeds into the garden. Since these materials can contain viable weed seeds, know the origin of your mulch.

Don’t apply mulch too early. Perennials should be dormant when you begin mulching them. Wait for the first hard or killing frost (below 25 degrees) before applying 2 to 4 inches of mulch, when perennials are shocked into dormancy. Mulching around them helps keep the ground frozen while shielding them from the sun’s warmth.

Remove the winter mulch in spring when all danger of a hard frost have past. Waiting longer produces leggy growth that will appear pale due to lack of chlorophyll from sufficient sunlight. There is also risk of suffocating the plant.