Resources: “Mulching Wood Ornamentals with Organic Materials,” Oregon State University Extension Service (EC 1629-E)

“Winter Care of Perennials,” OSU Extension Deschutes County, garden publications

Fall mulching can be the last garden chore you want to tackle. It might be rainy or windy or cold or snowy. With any luck it could be a warm balmy fall day. Whatever the weather, it is a chore that should be completed especially if you have new plantings of trees and shrubs.

Tree and shrub planting in the fall is a successful practice as long as the plantings are done with enough time to allow roots to adjust to the new environment. Equally important to the survival of a newly planted tree or shrub is the addition of mulches. Care should be taken to leave a few inches of soil unmulched around the base of the planting. Mulch piled around trees or shrubs increases the risk of fungal or bacterial diseases due to moisture being held near the bark. Trunk damage can also occur from voles and other pests munching.

The terms mulch and compost are not interchangeable. Compost, simply put, is nature’s own method of building soil fertility. Compost is usually turned into the soil, where Mother Nature takes over and decomposes the material, adding fertility and texture to the soil.

Mulch is a layer of material placed on top of the soil surface to conserve moisture, hold down weeds, offer winter protection and ultimately improve soil structure as it decomposes

Mulching protects plants during winter by reducing the dangers of freezing and heaving. The roots of unmulched plant material can be damaged by the heaving of soil brought on by a sudden warm spell followed by the return of normal cold temperatures. Depending on our winter that can be a critical issue contributing to plant loss.

There are various products available to protect woody ornamentals, each with different characteristics.

Mention mulch and most people associate the word with bark or bark dust. The most common bark products are Douglas fir and hemlock. The cost of hemlock is generally higher than Douglas fir. These are bagged products or sold in bulk. Several grades are usually available — including fine, medium, nuggets and rocks. The nugget and rock sizes are more expensive. However, they last longer and do not compact as much as the finer grades. Bark products tend to last longer and do a better job of controlling weeds.

Wood chips are made from the heartwood of a tree as opposed to the bark. They may be manufactured from Douglas fir, western red cedar, or hardwoods. Wood chips are a light color but turn gray with age.

Arborist mulch consists of the chipped branches and tree trunks resulting from a pruning or tree removal. The mulch is not graded, so it typically can contain small branches. The mulch is available at a low cost or sometimes free. Several years ago, our neighborhood was hard hit with fallen branches and trees, the results of a windstorm. I am still working out of the pile I negotiated for. Keep your eyes open for an arborist working in your neighborhood, providing you have space to have it dumped. Because of the lack of particle uniformity, it doesn’t have the aesthetic appeal of bark mulch or wood chips.

Fall mulches are applied after the ground has cooled. Adding too early will trap existing warmth and maintain active plant growth as opposed to going into a dormant cycle. Mulch is applied to a depth of three inches.

According to an OSU Extension Service fact sheet titled “Winter Care of Perennials,” many perennials do better without winter mulch as they are intolerant of being too wet. The list names over 40 perennials that should not be mulched. A second list of tender perennials names those that prefer extra mulch throughout the winter.

Composted grass clippings and leaves that have been shredded are more suited for perennials as winter protection. An easy way to shred the leaves is to rake into an area and run the lawnmower through the pile.

The bottom line is that developing a mulching program for summer as well as winter will reap the benefits in improved soil performance and healthier, stronger plant growth. In the end, it is worth the last back ache of the season.

— Reporter: