Monday, December 28th, 2015
When you, as a homeowner, have just planted a new tree on your property, one of the best things you can do for that tree is to place a nice layer of mulch under the tree’s dripline. To mulch means to place some type of material on the ground around the tree or other plant. Mulch can be either organic, which is preferable, or inorganic. Organic mulch materials will decompose over time and become part of the soil.
Organic Mulch Materials
Some common mulch materials are nut shells, pine needles, partially composted bark branches, leaves, and wood chips, or compost. We usually prefer hardwood mulch. A bark or wood chip mulch makes a good environment for soil microorganisms and earthworms. These mulches will decompose at different rates depending on the material, so they must be replenished periodically. You should not use grass clippings, sawdust, or straw as mulch around your tree.
Inorganic Mulch Materials
Some inorganic mulches are pulverized tires, ground fabric, lava rock, and decorative stone. They are good for xeriscaping and for protecting soil in high traffic spots, but aren’t so good for mulching around trees. The heat they reflect may kill some thin-barked trees. Never use black plastic or peat moss around a tree.
What Mulch Does
There are many great benefits to using a mulch around your tree, especially a newly-planted tree. Mulching will provide your tree with a more stable environment for the root system so it gets a good start.
A good organic mulch, such as shredded bark or partially composted wood chips, branches or leaves, will help the soil around the tree to retain moisture. This will cut down on evaporation and reduce the tree’s need for water. The mulch will also insulate the soil and protect it from fluctuating heat and cold temperatures. It helps to keep weeds and grass out, which would compete with the tree for the soil’s nutrients. Mulch keeps the soil underneath from hardening, eroding, or cracking. Roots will grow more quickly in soft soil than they will in hard soil.
Because an organic mulch decomposes slowly over time, it works to improve the soil fertility, aeration, and drainage, and will limit salt build-up. It protects the trunk of the tree from lawnmowers, weed-eaters, and any other lawn maintenance tools used. It will reduce tree diseases by protecting the part of the roots that are above the ground. Last but not least, it creates the appearance of a well-groomed yard.
Different Mulches for Different Trees
Some find it beneficial to use a mulch that is similar to the type of tree being mulched. In other words, if your tree is an evergreen or conifer, use wood or bark chips from a conifer. Likewise, if your tree is a hardwood, use hardwood mulch chips. A conifer has a different soil pH need than does a hardwood. Therefore, using hardwood mulch chips around a conifer could raise the pH levels to a harmful level for the tree. And the converse is true: conifer mulch chips may reduce the pH in the soil to an unhealthy level for the hardwood.
How to Mulch
If you have just planted a new tree, remove the grass around it to a three to ten foot radius depending on the tree’s size. You want the mulching area to match the tree’s dripline. If it is a new you tree you may have to increase the size of the mulching area as the tree grows.
Place the mulch a good four inches back from around the tree trunk. You don’t want the mulch touching the trunk because it will tend to increase insect and disease problems, rather than decreasing them. The mulch should be two to four inches deep, but no more. If it’s too deep, it will inhibit the exchange of gases between the air and the soil. If your soil is poorly drained, you may need to put down a thinner layer of mulch. When you are finished, the mulch should resemble a doughnut with the tree in the middle of the doughnut hole.
With all the benefits of mulching just listed, can there be any undesirable effects? Certainly! Just like with many things in life, there is a right way and a wrong way to mulch. And right and wrong mulching materials to use. Here are a few.
Over-mulching—putting down too thick a layer and/or allowing it to rest on the trunk—can kill rather than nurture a tree. Too much mulch can steal the water the roots need, block oxygen reception, kill the bark, allow root diseases, keep the trunk from hardening for winter weather, allow rodent damage, and encourage the formation of stem-girdling roots.
Over-mulching can also hold in too much moisture, causing root rot and other issues. It can kill the inner bark tissue, and lead to insect infestation. Too much mulch can provide a home for small rodents that will girdle the stem and chew the bark. It can also lead to a condition that will produce organic acids and alcohols that are toxic to a young tree.
Don’t use fresh organic mulches—those that haven’t been composted or leached. They can deplete the nitrogen in the soil, especially if the chips are small and put down too thick. Or they may be toxic, especially mulch made from cedar sawdust and bark.
On the other side of the coin, don’t use a mulch that smells sour. Organic materials should be well composted and aerated.
Stir up the mulch around your tree now and then to keep it from becoming matted and clumpy, keeping out the water and air that the root system needs. The mulch will look nicer, too, if you keep it turned and spread around evenly.
How you place the mulch will depend entirely on where it is placed, whether it is placed in a flat area, such as in the middle of your lawn. If your tree, and subsequent mulch area is close to a sloped spot, you will pay attention to the placement of the mulch. Even if it’s just a short slope down to a sidewalk or driveway, you don’t want the wood chips or other mulching material to fall out of its designated area. The use of decorative bricks or stones will make an attractive barrier that will keep the mulch in its proper place.