Mulching
Why it’s important for trees and how to do it
Mulching the area beneath your trees is a simple way to improve the health of your trees for a lot of reasons. It can help roots absorb more water and nutrients, improve soil, and protect trees from damage. There are different types of mulches you can use, and a correct way to apply it to avoid common problems. Always use organic mulch for your trees, rather than rocks, plastics, and other types of inorganic materials.
Benefits of Organic Mulching
Water and Nutrients
Using mulch to replace grass or other plants around the base of the tree reduces competition for water and nutrients, and can even make it difficult for weeds to grow [1]. It also acts as insulation preventing water from evaporating out of the soil [1]. Additionally, mulch can help prevent erosion and runoff, allowing the soil to absorb and retain water, making more water available to the tree.
Soil Improvement
Mulch breaks down over time which adds nutrients and amends the soil with organic matter [2]. Replenishing the soil with micronutrients reduces or eliminates the need for additional fertilizers. Amending the soil can reduce surface compaction and crusting, which is a leading cause of tree decline in urban areas [1].
Physical Barrier
Mulch also works as a barrier zone protecting trees from soil compaction, and damage to the trunk and branches by lawnmowers and foot traffic.
Where to get it
Best Option:
Coarse wood-chip mulch that is fresh or partially composted is the preferred type of mulch [3]. The easiest and cheapest way to get it is by having a tree service deliver it. Check out the Chip Drop app. This is usually good quality mulch, but you may get much more than you need if you’re not careful! If you have a way of picking it up yourself, wood-chip mulch is available for free at Idlewild Park.
With coarse wood-chip mulch, there may be a lot of twigs, leaf litter, and pieces of wood that don’t get chipped as finely, which can make your landscape look a little rustic. Use caution as some wood-chip mulch may contain plant diseases and allelopathic chemicals that may harm other plants [3]. There's also a chance that larger chunks (4" or more) of mulch can harbor insect larvae that may be harmful to your trees [4]. Always ask about the quality of your mulch!
Second Best Option:
An alternative to wood-chip mulch is bark mulch. It will break down faster and it needs to be replaced more often, but it's readily available at the Moana Rock Superstore located at 11301 S Virginia St, Reno, NV 89511 for $69/cubic yard. They don't use any dyes so the color is a natural brown that is a little darker than wood-chip mulch. Their local delivery fees range from $70-150. Click here to go to the page on their website.
Not Recommmended:
If you'd like another color mulch such as red, black, or another shade of brown, you can also get dyed mulch at Lowe's or Home Depot. Store-bought bags of mulch are more expensive and are often variable in quality. They can be any combination of wood, bark, construction debris, shipping pallets, and other junk, including chemically-treated wood. Definitely read the reviews and do a little research on different brands. Dyes used in dyed mulches are considered to be non-toxic and harmless to people, pets, and the environment [5]. Exact colors are not always consistent from one bag to another, so expect fading and blotchiness unless you mix it well yourself.
How to do it
Mulch should cover as much of the root zone as your landscape allows [3]. The root zone is the area under the tree, which extends at least as far as the spread, or width, of the tree, and often farther.
Mulch should be spread fairly thin and evenly, about 2-4” deep [3], and NEVER come in contact with the bark, or root flare at the base of the tree [3]. This can lead to infection, rot, and pest problems [1].
It's a good idea to add mulch at the time of planting, but you can always add mulch at any time.
For new plantings, you can add mulch on top of the dirt. For established trees, you want to avoid damaging the fine, absorbing roots of the tree by not removing the sod. It's better to cut the grass short and/or rake as much off as possible and add the mulch on top of the grass. Avoid plastic sheet mulching as it reduces the amount of water and oxygen in soil, leading to root rot [2]. If you must, cardboard may be better than plastic sheeting, because it breaks down faster.
Again, mulch should NEVER come in contact with the bark of a tree so do not shape it like a mound, which we refer to as a “mulch volcano”. This can restrict oxygen and water availability to the roots, leading to girdling and rot [1]. Instead, apply it thin and evenly across the ground. You can also shape it like a donut or a funnel for new plantings, to help retain moisture.
References
1. International Society of Arboriculture (ISA) Arborists’ Certification Study Guide, 2010
2. Mulching is Important for Tree Health. Michael Kuhns. https://forestry.usu.edu/trees-cities-towns/tree-care/mulching-tree-health
3. Tree Care Industry Association (TCIA) ANSI A300 (Part 2)- 2018 Soil Management (Fertilization)
4. Survival of Emerald Ash Borer in Wood Chips. https://www.nrs.fs.usda.gov/pubs/jrnl/2003/nc_2003_mccullough_002.pdf
5. Are Mulch Colorants Safe? https://www.mulchandsoilcouncil.org/information/mulch.php