The advantages of using organic mulch to blanket soil around trees, shrubs and perennial plants are many: Mulch moderate soil temperature and makes a more favorable environment for roots. It reduces evaporation of moisture, helping to conserve water.
Mulch also reduces splashing from rain or irrigation water, reduces the spread of disease and blocks the germination of many weed seeds. Beyond all that, mulch dresses up your garden, giving it a more finished look.
This article explores the kinds of hardwood mulches you can buy and their various advantages and disadvantages. Several hardwood and bark mulches are available; bark nuggets, mini-nuggets, hardwood mulch and shredded mulch.
Some come in bags, some in bulk. A chief advantage of these mulches compared with other organic mulches is that they remain attractive and functional for a couple of years. That’s why gardeners mulching around trees, shrubs and other long-lived plants are wise to choose long-lasting hardwood mulch.
Nitrogen Deficiency
Decomposing wood requires nitrogen. If you add a quantity of, say, fresh sawdust to your garden soil, your plants will probably suffer from a lack of nitrogen. In this case, the soil isn’t necessarily deficient, but the breakdown of the sawdust "induces" nitrogen deficiency in your plants.
Bark and hardwood mulches can also induce nitrogen deficiency, but it isn’t likely because they decompose at such a slow rate. It’s also unlikely because they are on top of the soil, not incorporated at root depth. But if this concerns you, or if your plants show the signs of nitrogen deficiency, add a 2-1-1 ratio fertilizer, such as 20-10-10, before mulching (2 to 5 pounds per 500 square feet).
Agricultural Byproducts
Exotic mulches are usually agricultural byproducts often (or only) available in bulk. One big advantage is their very low cost. Most are available only seasonally and in certain areas of the country. Some examples of these include cottonseed, buckwheat, corncobs, grape pomace, pine straw, pecan, walnut and rice hulls.
Although many exotic mulch are attractive and less expensive to use, they can be hard to find and may attract insects, such as ants. Plus, they tend to break down quickly. Ask your local Extension agent or garden center about the availability of this kind of mulch in your area.
Cost of Hardwood and Bark Mulch
Of course prices vary across the country, depending largely upon your distance from the source, the specific type of mulch, and local promotions. In general, expect to pay anywhere from $1 to $3 per 2-cubic-foot bag, or $3 to $6 per 3-cubic-foot bag. Buying in bulk saves money, but you’ll need to have your own truck. One pickup-truck load (about 1-cubic-yard) costs $14 to $25.
How to Mulch
Two good rules of thumb are to mulch with 3 to 4 inches of hardwood mulch each season and to avoid mulch layer buildup (and potential nutrient deficiency problems) by removing old layers of non-decomposed mulch before adding new layers. Coarse-textured mulches, such as shredded hardwood, can be applied thicker than fine-textured mulches, such as cocoa hulls. However, there are variations and exceptions related to the type of plants you’re mulching and your landscape situation.
Not Too Thick: Applying mulch around the base of your trees or shrubs is a good way to suppress weeds and will help retain soil moisture. But if the mulch is applied too thickly, the mulch itself will absorb rainwater and overhead irrigation, preventing that very water from reaching the tree’s roots. An overly thick layer of mulch can be an inviting environment for insects and even small rodents that can nibble on the tree’s bark.
Measuring from the soil surface, your mulch should be no more than 3-5 inches thick. Before applying a fresh layer in the spring, remove some or all of the mulch from the previous year and add it to your compost pile.
Not Too Coarse: Coarsely textured mulch (with individual pieces that are 1 inch or more in diameter) will not pack as tightly as finely textured mulch. Because wind-blown seeds—and light—can get between the larger pieces, coarsely textured mulch tends to be less effective at suppressing weeds. Small plants can also look dwarfed when they’re surrounded by big chunks of bark or 2-inch pieces of stone.
Mulching materials vary by region (bark chips and shredded bark mulch in the Northeast, pine needle and stone mulch in the South, compost and straw in the West). Use whatever mulch is most available in your area, but also consider matching the texture of the mulch to the size and type of plants you are mulching around.
Mulching Your Plants
Whatever the type of plant, it’s rarely advised to mulch more deeply than 6 inches. Hardwood mulch layers thicker than that might reduce air circulation in the soil, which will retard plant growth. Also, don’t pile mulch around the main stem of a plant where it enters the soil. The added moisture and insect haven that results could damage the plant you’re trying to help. Spread the mulch so that it covers the "dripline" of your plant.
Landscape Situation
Which mulch you choose depends on the site:
Areas Prone to Flooding: Nuggets last many years without breaking down, but they’re not useful in wet areas or on steep slopes because they float and wash away easily. Similarly, don’t use the fine particle mulch, such as cocoa hulls, in windy or seasonally flooded areas since they can blow or float away easily.
Slopes: On steep slopes, shredded mulch is best, and hardwood holds better than softwood. However, hardwood mulch tends to break down faster than softwood and may need to be reapplied sooner.
Pathways: For easiest walking, use shredded hardwood or pathway hardwood mulch. The irregularity of shredded hardwood and the small particle size of pathway hardwood are better for walking compared with mulches with larger particle sizes.