All About Mulch | Aspen Arboriculture
Home Ideas Magazine - September 2017
MULCH: IS IT GOOD OR BAD FOR YOUR TREES?
I always recommend that a tree be mulched for improved long-term health and reduced stress. However, how the mulch is applied and what types of “mulch” you use can have drastic, even harmful effects on tree and plant health. This article focuses on proper mulching techniques and tree health, but the principles will actually apply to just about all landscape plants.
When it comes to your tree’s root system, in the context of optimum health, competition
from turf grasses is the biggest challenge. Having an open area that extends to the drip-line (the area from the edge of the canopy in to the trunk) that is free of turf and has a two to four-inch layer of decomposable wood mulch, has been shown to increase size of a trees root system by 400%. So if you want your trees to be as healthy as possible, mulching is a no brainer.
HOW TO MULCH CORRECTLY
For optimum tree health, there is no "carefree" mulching solution. You will need to maintain the mulch and do a bit of weed pulling/spraying. But if done correctly, you can manage any yard with a few hours, twice a year.
Mulch is best applied directly on top of the soil or turf with no weed barrier fabrics or plastic. Just keep in mind that the highest concentration of fibrous roots are nearest the trunk and within the drip-line. The area of mulch should be flat and even. There should be a small gap
between the mulch and the trunk with the mulch rising rapidly up to the two to four-inch level, then flat out to the desired distance, dropping off rapidly to the soil. You may use edging if it suits you, or you can spray the grass on the outer edge with glyphosate (roundup) to keep the grass out of the mulch.
I have found that a shredded hardwood mulch works the best in our region. It will not blow away if put down thick enough and watered. You can use other mulches, but make sure it will actually decompose. Avoid rubber mulches or plastic rings designed to hold in the mulch, as they do nothing to help the tree. I would also avoid using grass clippings, coconut hulls, and bark chips. The grass will often get too thick of a mat and limit oxygen to the roots. This causes an anaerobic decay state, which not only makes a bad smell but will cause harm to root growth. Coconut hulls do not decompose or hold enough moisture to be of any significant benefit; and the bark chips are similar. Plus, both will blow away.
A plastic barrier will prevent moisture and, more importantly, oxygen (roots need oxygen to survive) from getting down into the soil. It can also hold excess moisture and promote bad fungi to growth, essentially sterilizing the soil. Landscaping fabric has been shown to do similar things. Even though it is designed to let water and air through, it doesn’t do the best job at it and is
almost just as much a stressor as turf or rock. Fabric creates a barrier between tree roots and beneficial fungi (Mycorryzea) within the soil. Micorrycal relationships benefit the trees by helping them absorb more nutrients and water from the soil than without. Rarely (especially in our soils) is poor plant performance due to nutrient deficiencies, it is most likely due to poor soil health.
Providing the mulched area around the trunk, without fabric, has these amazing benefits for tree health:
- Allows mycorrhizae to form
- Promotes the largest root system the tree can grow
- Retains soil moisture
- Reduces competition for water and nutrients from turf
- Regulates soil temperatures
- Naturally balances the soil pH over time
- Decompacts the soil allowing for larger and deeper root systems
- Prevents mechanical damage to the tree trunk from lawn mowers and string trimmers
A mulch volcano is where the mulch is applied in a big pile up next to the trunk, tapering off out away from the trunk. Mulch should never be up next to the trunk because it causes the roots to circle around the trunk and eventually girdle (choke) the trunk, killing the tree. This practice should be avoided at all costs, it causes more harm than no mulch at all.
Healthy and well-maintained trees increase property value, are less disease and pest prone, and will last many generations. Mulch away!
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