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Winter Mulch


If you havenít 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 landscapeís 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 soilís 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 natureís 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 Natureís 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, doesnít 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.

Why mulch in winter?
The answer: for all the same reasons you mulch in the growing season and more. While you are thumbing through gardening catalogues waiting for spring, it is encouraging to look at a neat and well kept garden. From a psychological standpoint it helps get us through the long, dreary, gray days of winter.

The primary reason for winter mulching is to protect our plants, especially new plantings, from the harsh conditions of winter freezes, thaws and winds. The fluctuating temperatures plants encounter during the winter can injure or kill them. When the ground repeatedly freezes and thaws, it expands and contracts loosening plant roots. Roots are what anchor the plant under ground. When they become loose the plant will eventually heave through the surface exposing its crown and roots to the frigid temperatures and drying winds. Plants become stressed and vulnerable to disease later on.

A layer of mulch will minimize soil temperature variations, thereby reducing heaving. The even temperatures will also reduce early growth from being injured or killed by late freezes. Mulching for winter also means less rapid weed growth in early spring.

Donít 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 sunís 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.

Organic mulch is the best material for winter. If using leaves, use only stiff leaves such as oak or beech. Soft leaves, e.g. maple, pack together making it difficult for air and water filtration.

For trees and shrubs: apply 2 to 4 inches of mulch. Keep it away from stems and crowns. Piling mulch at the base of a plant holds moisture against the plant providing ideal conditions for bacteria, rot and disease. Too much mulch also creates a home for rodents and insects who feed on bark. These unfavorable results can become a bigger problem during the cold season when critters, diseases and spores are looking to overwinter. For perennials and bulbs: use straw, shredded leaves or evergreen boughs.

The Leonard J. Buck Garden uses evergreen boughs from recycled Christmas trees as winter mulch. Boughs are easy to apply, easy to remove and they are free. Removed them at the beginning of April.

Insulating your plants from winterís icy blast will make a big difference in the garden. Winter mulch encourages healthier plants in spring and summer and provides some beauty for the winter landscape.

As we wait in anticipation of spring, the rich, warm tones of a winterís blanket will relieve the long, drab, dreary days of winter.

- Tricia Scibilia, interpretive gardener, Leonard J. Buck Garden, Somerset County Park Commission: www.somersetcountyparks.org
**Photos by Tricia Scibilia unless otherwise noted

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