For as long as trees have grown in forests, leaves and needles have fallen to the ground, matted together, and formed a natural protective layer over the soil. This protective layer is beneficial for trees. You can do something similar for your landscape trees by mulching around them.
Mulching can help trees by:
- providing a root environment that is cooler and contains more moisture than the surrounding soil.
- reducing competition from surrounding weeds and turf.
- providing some food for the tree as it decomposes into the soil
- preventing mechanical damage by keeping machines such as lawnmowers away from the tree’s base
- reducing soil erosion around the tree and contributing to healthier soil structure.
When and How to Mulch
To get the best results from your mulch, layer it two to four inches and cover the entire root system, which may be two or three times the diameter of the branch spread of the tree. If you cannot mulch the entire area, try to mulch as much of the area under the drip line of the tree as possible. Do not cover the actual trunk of the tree with mulch. Leave a one or two inch space to avoid overly moist bark conditions that cause trunk decay. More than five inches of mulch can cause a problem for your tree, as it could inhibit gas exchange.
Before covering an area with mulch, bring the site to its desired grade. Mulches applied for winter protection should be laid down in late fall, once the soil has cooled but before it has frozen. Summer mulches are normally applied in mid-spring, once the soil has warmed enough for active root growth.
Mulches that are left around trees and shrubs year-round should be pulled away from the trunks in the fall to allow proper hardening of the bark.
Thoroughly cover an area to a uniform depth to be most effective. Low or bare spots are prone to weed problems. Uneven mulch does not properly insulate the soil.
Although there is no super-mulch, knowledge of the characteristics and uses of different mulches allows a gardener or landscaper to use mulches to benefit the entire landscape.
Characteristics of a Good Mulch
There are many different natural and synthetic mulches available. Mulches can be made or purchased.
The ideal mulch is:
- Economical.
- Readily available
- Easy to apply and remove
- Stays in place
- Supplies organic matter to the soil
- Free of noxious weeds, insects, and diseases.
It also suppresses weeds, conserves soil and water, and moderates soil temperatures. Does such a super-mulch exist? Not really.
Consider:
- Black plastic, which warms the soil in spring, also heats the soil in summer, possibly to levels that are lethal to plants.
- Straw, shredded leaves, pine needles, and wood chips are effective insulating blankets in winter, but they slow soil warming if left on in the spring.
- Although black plastic effectively prevents the evaporation of water from the soil, it also blocks the entrance of water into the soil.
- Mineral or synthetic mulches do not contribute beneficial organic matter to the soil, but some organic mulches may contribute weed seeds and diseases to a site.
Another consideration is choosing the right mulch for the location:
- Straw is commonly used in vegetable gardens or small fruit plantings.
- Wood chips, bark chunks, and pine needles are appropriate mulches for shrub beds or around trees.
- Fine mulches, such as bark granules, wood shavings, cocoa shells, and buckwheat hulls, are attractive when used in annual or perennial beds.
- Fine gravel or crushed stone mulches look most natural when used in rock gardens.
Other considerations in selecting mulch are cost and availability. Although cocoa hulls and buckwheat hulls make very attractive mulches, they may only be sold in regions where these commodities are processed. Even when available, these mulches are normally more expensive than wood chips or bark products. On the other hand, some municipalities stockpile wood chips from tree-trimming work and offer the chips free to anyone willing to haul them away.
Types of Mulch
Bark mulches
Commercial bark mulches are generally the by-products of milled fir, Douglas fir, pine, redwood, and spruce logs. Three grade standards have been adopted for landscape use based on particle size:
- Bark Chunks(decorative bark)
- Bark granules(soil conditioner)
- Shredded bark
Some bark mulches may be toxic to young plants, particularly if the bark is fresh or if it has been improperly stockpiled. Toxins can be leached from bark by heavy waterings or can be evaporated by thorough aeration. Bark mulches are most likely to cause damage to plants if the mulch particles are small, if the mulch is too deep, or if high proportions of plant roots are in the surface layer of the soil. |
If you are concerned about the toxicity of fresh chips, spread them thinly under young plants. Bagged bark mulch products have usually been allowed to weather for long periods of time to remove any toxins and are least likely to harm plants. |
Among the most desirable characteristics of bark mulches are their excellent resistance to compaction and blowing in the wind, their attractiveness, and their availability |
Wood chips Wood chips are derived from many different hardwood ![]() |
Sawdust ![]() |
Hulls of cocoa, buckwheat, cottonseed ![]() |
Straw Straw from wheat, timothy, oats, rye, or barley is widely available and comparatively inexpensive. It is used as a winter mulch around tree or shrub roots and as a summer mulch in vegetable gardens and strawberry plantings.Straw has some potential problems that you should be aware of before using it.
Straw:
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On the other hand, it is cheap and effectively suppresses weeds and reduces soil water losses. As a winter mulch, it protects tender roots from cold temperature injury. |
Pine Needles ![]() |
Shredded leaves ![]() |
Crushed stone, gravel, volcanic rock ![]() |
A couple words of caution: mineral mulch particles can work free of beds and be thrown by rotary lawn mowers, potentially causing injury. Unless underlaid with a synthetic fabric or plastic mulch, they migrate down in soils over time. Limestone chips raise the pH of the soil and thus should not be used around acid-loving plants. |
Black plastic ![]() |
Geotextiles (or Landscape Fabrics) ![]() |
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Some factors to consider are:
- Ease of applying the material to the landscape.
- Ease with which water penetrates.
- Effectiveness of the material in suppressing weed growth.
- Relative cost.
- Before a geotextile is applied, the area to be mulched should be cleared of all weeds. Most manufacturers direct the applicator to lay down the fabric and cut slits where plants are to be installed.
Landscapers who have worked with geotextiles, however, have found that application is easiest when shrubs are planted in weed-free soil first. Then the fabric is laid on top and slits are cut that just allow the fabric to be worked around the base of each plant. The final step is to apply a 1- to 3-inch layer of mulch on top of the geotextile to improve appearance, reduce wear, and decrease deterioration by the sun’s rays. Although geotextiles are a great advance in mulching technology, they don’t prevent all weed growth. Weeds that germinate and grow in a bark or wood chip top mulch can grow right through the fabric. Especially troublesome weeds are grass or grass-like species such as nutsedge and bermuda grass. To maintain a bed mulched with a geotextile effectively, remove weeds when you see them. |