Types of Mulch | How to properly mulch your plants | What not to do when mulching your plants

Proper mulching is very beneficial to your plants. It retains moisture, which is very beneficial during warm weather and times of drought, and keeps soil temperature more consistent and insulates the soil to help protect roots against extreme summer and winter temperatures. As it decomposes, certain types of mulch improves the soil by adding nutrients back to the soil and helps keep improved soil from washing away. It also reduces the likelihood of any damage from weed and lawn mowers.

Types of Mulch

Mulches are available in many forms. The two major types of mulch are inorganic and organic.

Inorganic mulches include various types of stone, lava rock, pulverized rubber, geotextile fabrics, and other materials. These mulches do not decompose and do not need to be replenished often. On the other hand, they do not improve soil structure, add organic materials, or provide nutrients. For these reasons, most horticulturists and arborists prefer organic mulches.

Organic mulches include wood chips, pine needles, hardwood and softwood bark, cocoa hulls, leaves, compost mixes, and a variety of other products usually derived from plants. These mulches decompose at different rates depending on the material, climate, and soil microorganisms present. The faster the mulch decomposes, the more often it will need to be replenished. Since the decomposition process improves soil quality and fertility of the soil, many arborists and other landscape professionals consider that characteristic a positive one, despite the added maintenance.

How to properly mulch your plants

The choice of mulch and the method of application can be important to the health of landscape plants. The following are some guidelines to use when applying mulch:

Determine whether soil drainage is adequate and if there are plants that may be affected by the choice of mulch. Most commonly available mulches work well in most landscapes. Some plants may benefit from the use of slightly acidifying mulch, such as pine bark. 

Spread mulch 2-4 inch deep to well-drained areas or less if poorly drained, never directly against the base of the plant. Coarse mulches can be applied slightly deeper without harm.

For trees, spread mulch 2-4 inches deep to the drip line of the tree if possible; do not let the mulch touch the trunk. The mulch should form a flat donut with the trunk in the center. Another guide is the “3x3x3 rule” or 3 inches of mulch, 3 inches from the trunk, in a circle 3 feet wide. Organic mulches (bark mulch, wood chips, leaves, etc) are preferred over stones or other inorganic products.

If mulch is already present, check the depth. If sufficient mulch is present, break up any matted layers and refresh the appearance with a rake. 

If mulch is piled against the stems or tree trunks, pull it
back several inches so that the base of the trunk is exposed. Composted wood chips can make good mulch, especially when they include some bark and leaves. Fresh wood chips also may be used around established trees and shrubs. Avoid using fine, non-composted wood chips, as soil nitrogen may be taken up by the roots as the wood chips decompose.

What not to do when mulching your plants

As beneficial as mulch is, too much can be harmful. The generally recommended mulching depth is 2-4 inches. Unfortunately, many landscapes are falling victim to overmulching or volcano mulching, especially around trees.

Volcano Mulching is an improper mulching technique where mulch is piled high around the base of a tree and sits against the trunk. Yes it may look nice, but it will slowly kill your tree. Mulch should not touch the trunk of the tree. The trunk was simply not meant to be covered and doing so invites disease and decay due to moisture retention on the trunk and pests, such as bugs and rodents, that can cause damage to the tree.

While organic mulches must be replenished over time, buildup can occur if reapplication outpaces decomposition or if new material is added simply to refresh color. Deep mulch can be effective in suppressing weeds and reducing maintenance, but it often causes additional problems, such as root rot. On wet soils, deep mulch can lead to excess moisture in the root zone, which can stress the plant and cause the roots to rot. Failure to develop a normal root flare which stabilizes the tree is another problem caused by too much mulch and may cause the tree to fall during a storm.

Piling mulch against the trunk or stems of plants can stress stem tissues and may lead to the development of stem girdling roots. This is harmful to the tree because these girdling roots will circle around the tree and eventually choke off the tree’s main roots. It also leaves these roots exposed and unprotected when the mulch decomposes.

These problems are not limited to just trees, it can affect shrubs and other perennial plants as well. You should never put mulch directly against the base of any plant to help prevent these problems and to keep them as healthy as possible.

Another tips to remember is, when mulching around any type of tuberous plant, such as iris tuberosa or begonia tuberosa, never put mulch over top of tubers. This will cause harm to the plants and can cause the plant to die.