August 2, 2021

Mulch can provide a variety of important benefits for your ornamental trees and shrubs. The basic principles for using it correctly are fairly straightforward, but many people are not familiar with them. As a result, some people deploy mulch in ways that can cause damage, while others avoid it altogether. Here are a few tips to help you use mulch to enhance the health and appearance of your landscape.

The Best Mulch for Ornamental Trees and Shrubs

To choose a mulching material, first consider its intended use. Wood chips, for example, are among the best choices for ornamental trees and shrubs. They help to regularize soil temperatures, insulating against both extreme heat and cold. They’re an attractive addition to a landscape, providing variation in texture and color. They’re long-lasting and provide an excellent balance of nutrients as they break down. However, one of the helpful functions of mulch is helping to maintain moisture in soil, and wood chips absorb more water than other mulches. In addition, fresh wood chips (as opposed to aged ones) leach a lot of nitrogen from soil, reducing the amount available for plant nutrition. Thus, wood chips are not a good choice for annuals or vegetables.

More Mulch Benefits

Pine needles also offer a tradeoff. They’re very cheap, especially if there’s a pine tree nearby. Be aware, though, that while pine needles break down very slowly, they will need to be replenished more frequently than wood chips would. On the up side, they don’t absorb nutrients or water from soil; on the other hand, they’re not heavy enough to slow normal evaporation.

In past decades, peat moss was used as a mulch, but this practice has declined. This is partly because it has already decomposed quite a bit by the time it arrives in our garden stores and has very few nutrients left to release. In addition, it’s not renewable, unlike other mulch options. Today it is more commonly put to work as a soil amendment.  Although it offers little nutrition itself, it does help soil retain water and the minerals that the water has absorbed.

Other options favored by professionals include pieces of bark, cocoa hulls, leaves, compost, and pieces of bark.  Hardwood bark or chips are appropriate for any type of ornamental tree or shrub, while their softwood equivalents should be reserved for larger varieties in both categories. Pine is the most common softwood, and its relatively high level of acidity reduces its already slow rate of decomposition. Hay should be avoided, as it often contains invasive seeds.

How Much Mulch?

It’s not clear why, but the temptation to apply too much mulch is extraordinarily strong and common. Multiple layers of wood will help the soil retain the moisture it already has but inhibit rain from reaching ground level. Large piles of mulch can also reduce the flow of oxygen to roots and encourage the growth of harmful funguses and pests. In almost all cases, two to three inches of mulch will produce the best results.