This month’s Tree Tip was researched and written by Emil Peter, Director of Plant Health Care Services, ISA Certified Arborist #SO-6363A, and Forester for Woodland Tree Service. He may be contacted directly via email with any questions concerning this article or any other tree related issues.
Mulching and composting are two of the most beneficial and cost effective things a homeowner can do for the health of any tree. Mulches are materials placed on the soil surface to improve soil structure, oxygen levels, temperature, and moisture availability. Properly applied, mulch can give landscapes a handsome, well-groomed appearance in addition to slowly fertilizing and improving the soil structure around your tree.
In order to be as effective as possible, mulch must be applied properly. If the mulch and compost layers are too deep, or if the wrong material is used, it will cause harm to trees and other landscape plants. The combined compost and mulch should be about 2 inches deep and made of an organic material such as wood chippings or pine straw or even just leaves and sticks from the yard. You will want a material that will break down over time and return it’s nutrients to the soil around your tree.
As for how large an area around the tree to mulch, I recommend mulching as much of the root zone as possible. This will do a couple of things:
- Historically, trees grew in the forest and forests have what is referred to as a litter layer. This litter layer is little more than a continuous compost pile. The leaves and sticks and dead trees and other materials shed by the trees every year slowly break down around these trees and keep the nutrient cycle going.
Over time, we humans decided we liked having the benefits trees and the forest provided close to our homes and buildings. So we planted trees in our yards and parking lots. That’s all well and good, but we surrounded those trees with grass or asphalt. We rake up their leaves and sticks and acorns and flowers and everything they shed to form that litter layer in the forest; essentially we remove their compost pile and the nutrients that break down in that system are pulled from the soils of our lawns. This depletes the overall nutrient availability in the soils of urban areas and also destroys the soil structure making it more difficult for roots of any species to set in and find good pathways for growth. Placing mulch in the root zone is a start to replace this litter layer, but allows us to control the amount and still keep our lawns looking nice.
What to Look Out
for This Month:
- Southern red mite
- Crape myrtle aphid
- Asian ambrosia beetle
- Spruce spider mite
- Orange-striped oakworm
- Speaking of lawns, mulching and composting a larger area, say, everything under the canopy of the tree inside the drip line, keeps you from having the never ending fight with grass not growing around your tree and then having bald spots in your grass and fighting to keep grass growing there. Here is just a small philosophy about the eternal struggle of Grass v. Tree: Trees are bigger. Bigger things are generally better competitors. Trees will out-compete grass every time for the three things they both need: 1. Light, 2. Water, & 3. Nutrients. Why fight that fight? Give the trees their space and give the grass its.
- In addition to not having to over-seed and re-sod every year or so, since the grass is away from the trunks of the trees, there is no need to beat the tree up with the string trimmer. This type of damage is commonly referred to as “Weed Whacker Blight” and can kill trees, especially when they are young. Why take that risk of killing your tree just as it is getting started? Keep grass away from the tree and you keep string trimmers away, too.
Questions on How to Mulch? Here is How:
- Pick an appropriate time to mulch. Mulch annually in spring before soil moisture decreases and temperatures increase or in late summer/early fall. Mulch Prior to, during and after construction or infrastructure changes affecting tree roots and tree health. Mulch after tree injury. Or mulch because you feel like it.
- Find and a good quality mulching material. Organic materials are preferable to inorganic materials but when organic mulching materials decompose, they must be replenished. I recommend these mulches: Wood chips, pine needles, tree bark, leaf mold or compost.
- Always use this mulching method: Apply mulch in a circle covering the entire root system of a tree. Most of the fine, absorbing roots of a tree extend well beyond the tree canopy, or drip line. The general recommended mulching depth is 2-4 inches. Keep mulch off from from the base of the tree trunk to help reduce the chances of root rot fungus growth.
- Make sure you are not doing this: Mulching with a deep layer of material (over six inches of material). Mulching with piles high against the trunks of young trees. This can lead to insect and disease problems.
- Think about how mulching benefits the tree by:
- Conserving moisture
- Improving soil structure
- Reducing soil compaction
- Increasing soil aeration
- Increasing the available nutrients
- Suppressing grasses and weeds
- Making the arborscape attractive
- It helps prevent damage from mowers and weed whackers
Still have some questions? Here are a few Do's and Don’ts:
1. Don't fall into the trap of the dreaded "mulch volcano," especially with young trees.
You've probably seen mulch volcanoes on people's lawns. Folks build circular raised beds around their trees, then fill the raised beds with wood-chip mulch. The mulch gets steeper and steeper the closer it gets to the tree, which shoots out of the hole at the end like a lava eruption! In a typical mulch volcano, the mulch may be 2" high at the perimeter and 6" high up close to the trunk.
There are several problems with mulch volcanoes:
- Water runs off the sides of the mulch volcano and away from a young tree's base (which is where all its roots are, for now), thus depriving it of water.
- 6" of mulch is too deep. Much water that would otherwise reach the tree's roots gets trapped in the mulch.
- Excessive tree mulching invites rodent pests and diseases.
- Excessive tree mulching can even suffocate roots.
2. Don't mound up dirt or mulch around the trunks of trees.
Piling up mulch against tree trunks can cause harm to your trees: it invites diseases and rodent pests. If you are mulching around a tree, start tapering the height of the mulch down when you get to within about 1' of the trunk, leaving the base of the tree free of mulch. It would even be better to have to weed this 1' than to risk damage to your tree, wouldn't it?
1. Do apply about two inches of mulch around trees, especially young trees.
Mulching trees keeps down weeds, thus eliminating competition for water. In addition, much water that otherwise would be evaporated by the sun can soak down through a 2" layer of mulch to the soil around tree roots. Mulching trees also helps keep their roots cooler in hot weather.
2. Do use shredded leaves when possible in mulching trees, especially young trees.
There is absolutely nothing wrong with using wood-chip mulches. However, a shredded-leaf mulch has some advantages. First of all, it is free. When you rake up your leaves, put them through a leaf shredder or leaf vacuum if you already own one; otherwise, shred the leaves by running the lawn mower over them. Secondly, leaves break down faster than wood chips, thereby releasing nutrients faster. Young trees, especially, will appreciate those nutrients. If you do not have one of these options or would rather have us take care of raking up your leaves and shredding them for compost, we would be happy to do that.
Our arborists want to keep your trees healthy for years of your enjoyment. If you have any questions or need any assistance with your trees, pests, or just questions, contact the experts at Woodland Tree Service. Email us or call (901) 309-6779.