Mulching timber: good or unhealthy?

Humanity depends on trees for oxygen, shade and food. They play an incredibly important role in our lives. They are often large and sturdy, which can give a sense of security, which is why they often symbolize peace and protection. It takes several years for trees to reach this robust state and they rely on us to be looked after until then. Young trees need consistent watering, pruning, and a good layer of mulch around the trees.

Mulching trees is critical to making sure a tree is happy and healthy, but there is a lot of misinformation and misunderstanding on the subject. Improper mulching, such as a mulching volcano, can be fatal to the tree due to the risk of excessive moisture on the bark of the tree trunk. But if done correctly, mulching can cause your tree to thrive and the surrounding soil to improve.

Let's take a look at the pros and cons of mulching around shrubs and trees, as well as the appropriate methods for applying mulch. There are right and wrong methods and good and bad mulching materials.

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Why should you mulch around trees?

Shallow mulch like this one can be used as long as it is not piled up around the trunk. Source: Andrew W

Mulching trees has many benefits. From preventing unwanted grasses and weeds to helping the roots get more oxygen, there are many good reasons to spread mulch around a tree.

Reducing moisture loss in the soil

The soil around a tree needs to hold moisture, especially when the tree is young. Spreading mulch around the tree is a key component in retaining moisture. The sun evaporates water as it precipitates, especially during the heat of the day. A layer of mulch prevents the sun from hitting the ground and keeps the water in place longer.

Mulch is also responsible for holding in water, which allows the soil to absorb more. When it is compacted, water can run off and not be picked up close enough to the tree. Mulch helps contain water around the tree.

Gradual improvement of the soil

Over time, the mulch layer improves the quality of the soil. When you use organic mulch, it breaks down and adds nutrients that nourish the tree. Organic matter also holds nutrients that are already there, so you don't have to fertilize as often.

Mulch can prevent and reduce soil compaction around your tree. If you choose wood chips, pine needles, or any other bulky material, it will be pushed into the ground when you or animals walk over it. The soil needs to be loose so that the roots can grow more easily and take in oxygen. Mulch is a pretty effortless way to improve clay soils.

Prevention of erosion

Just as soil helps prevent soil compaction, it can also prevent soil erosion. If you've ever stumbled upon a weather-exposed tree root, thank the erosion for that. Wind, rain and settlement erode the soil and will eventually release roots. Mulch prevents this, which keeps the tree roots protected and prevents you from falling. Thank you, Mulch!

Reduces the floor temperature

Nobody likes it when the sun is shining, and neither does trees. A thick layer of mulch acts like an air conditioner and prevents the soil from getting too hot. This allows the roots to function normally and also supports root growth.

Reducing disease

Mulch encourages beneficial fungi to grow. While many novice gardeners believe that having a fungus among us is a bad thing, it is actually a sign that your soil is healthy and that the mulch is doing its job. Some mushrooms are disease suppressive and prevent pathogens, which makes your tree less likely to get sick.

It also prevents the spread of disease by acting as an obstacle course for disease-infested pests. Restricted mobility makes it difficult for pests to reach the tree.

Protection from weather

Similar to how mulch prevents erosion and hot soil, it also prevents the roots of the tree from suffering direct weather damage. A couple of inches of mulch above the root system will keep them covered so they're not exposed to sun, heat, or cold. The roots of the tree will stay safe this way.

Weed suppression

A few inches of mulch can suppress grass, weeds, and other plants that would otherwise take up nutrients that would benefit the tree. If the grass or weeds are left untouched, they can even inhibit the tree's root growth. In addition, grass and weeds in a landscape are visually unattractive, so a win-win situation for you and your tree.

Problems with mulching

Irregular mulchingIrregular mulching may not reduce weed competition, but it is a common choice for landscaping. Source: Andrew W

It is possible to use too much mulch and then you will run into problems. You will have minimal (if any) problems if used in a reasonable amount. So make sure you only use enough. We'll cover how much to use in the next section. So let's first look at the things that can go wrong.

Water damage

Mulch is used to hold back water, but sometimes it can hold back too much. Deep mulching can run the risk of not getting oxygen into the trunk or root system of your plants. Young trees need more water than mature trees, but they should never be in moist soil.

Pest damage

Too much wood shavings around the tree trunk can attract pests such as termites, bark beetles, and bores, which eat up the tree bark and cause trunk damage. Protect the health of the trunk of your tree by keeping the mulch a few inches away.

Disease damage

Fungal and bacterial diseases can thrive in humid environments. We mentioned beneficial mushrooms in mulch earlier, but bad ones can also occur. It is important that you keep moisture levels in check and provide some sort of landscape barrier around the bottom of the trunk to prevent your mulch from putting the trunk at risk.

Wrong temperature

Mulch regulates the temperature unless the layer is too deep. This can cause the soil to get too hot and damage the roots. Too much mulch can also lead to a pH imbalance that affects the health of your tree.

Travel mulch

Children, pets and nature itself can move your mulch. It can help to have landscape edges or a tree border to keep your mulch in place.

How to properly mulch trees

Volcano mulchesThe volcano mulch shown here is dangerous for the tree trunk. Source: skvidal

If you are new to tree mulching or trying to correct mistakes made for years, it can be difficult to strike the right balance between too little and too much. Let's look at how to properly apply mulch.

Types of mulch

Before laying out mulch, choose what type of mulch you want to use. We strongly recommend organic mulches filled with organic matter as they will eventually break down and increase the nutrients in your soil. Better still, they don't harm the environment like some synthetic mulches can.

Great organic mulching options include:

  • Wood chips: These are often available cheaply or even free of charge if you contact an arborist or recycling center and ask about them.
  • Straw: Straw is light and quickly decomposes, so vegetable gardeners prefer it, but it can certainly be used on trees and shrubs. You have to renew the layer frequently because of its rapid decomposition. One disadvantage is that it can contain seeds that will germinate.
  • Crushed leaves: Trees make leaves, so why not give them back to the tree? If your own trees aren't enough, your neighbors will likely appreciate your taking them away from them. Shredding is critical so you can prevent compaction.
  • Pine needles: Much like shredded leaves, these are an excellent free resource. They're slowly decomposing so you only need to update the layer once or twice. They acidify the soil, which can lead to a pH imbalance.
  • Crop residues: The husks and scraps of cocoa, cottonseed, and buckwheat are nice mulch choices, but they have problems. They are expensive and can attract pests in humid regions. Cocoa shells have a chocolaty odor, but can be toxic to pets.

You can use synthetic materials or mineral mulches around trees and shrubs if you want, but they have their drawbacks. Mineral mulches like gravel or stones help prevent compacted soil and stop weeds, but you risk breaking a window with the lawnmower.

Synthetic mulch like black plastic, rubber, or geotextiles will stop weeds and water evaporation, but it can also lead to water retention. Some also degrade due to UV rays or contain pollutants that damage the soil. They don't give anything back to the soil when they are mined.

Layer thickness

At the very least, you should have at least a 2-inch layer of mulch. Try not to exceed 6 inches deep or you may experience the problems mentioned above. A 2-inch layer doesn't sound like much, but it's enough to reap the many benefits of mulch. 4 inches is better, and 4 inches deep gives you excellent moisture retention and weed control.

Mulch should be at least 5 inches from the tree trunk and run around the trunk. We recommend spreading it out as wide as the canopy of the tree, but you can make it as wide as you'd like or a little thinner. A young tree's roots are not that widely spread, so it will likely be well covered in a circle of mulching a few feet in diameter.

Round off

Mulching is not a one-time job. You need to fill it up, especially if you are using organic mulches. Remember, you will need a 2-4 inch layer of mulch. So when you see that it's thinned out, it's time to add more to the landscape.

Every mulch has different requirements. Straw mulch needs to be replaced almost monthly, while pine needles only need to be replaced once or twice a year.

Avoid volcanic mulches

Unfortunately, many people think that a lot of mulch is good, so they create a mulching volcano around the base of the tree instead of spreading it over the root system. As we discussed, this is bad for a number of reasons. A mulch volcano builds up too much moisture and can quickly damage the tree bark because it is on the tree. Using a log protector to keep the mulch away from the bark can help.

Roots spread out from the tree trunk rather than growing straight down, so the mulch layer should reflect this to benefit all roots. A mulching volcano doesn't protect your landscape or reduce weed growth, and you're just creating a risk that you don't need.

frequently asked Questions

Q: Should I mulch around old trees?

A: Mulching old trees prevents the spread of disease and pests, reduces the spread of weeds, and reduces the need for fertilizer when you use organic mulch.

Q: Is it bad to mulch around trees?

A: When properly applied, mulch will help the tree a lot. Too much is a bad thing, however, and it can spread disease to your tree trunk.

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