Trees improve water quality by slowing and filtering rain water as well as protecting aquifers and watersheds.
The single most beneficial thing you can do for any tree is to mulch it properly.
Mulching is the application of material on the ground in an area where plants are growing. Various materials can be used according to the desired outcome.
In natural settings, trees drop their leaves right around themselves and can absorb nutrients as they decay. In this way, trees treat their waste as food-recycling the nutrients that they lose in their leaves each year to help grow new leaves in the future.
In the city, we plant trees in what are frequently compacted, unnatural soils surrounded with concrete, gravel and are often subject to littering and animal waste. Mulch improves the tree’s living conditions in the city; it breaks down to provide nutrients for the tree, while also yielding a host of other benefits.
“How much should I mulch?”
The more area you mulch, the more your trees will benefit. Landscape standards generally call for mulching to the ‘drip line’ of the tree, or to the edge of the tree’s leaf canopy. This may be impractical if you have a large tree in your yard whose canopy spans the entire lawn, so a smaller circle may be more appropriate. The more area that you mulch the greater long-term improvement in tree health and growth you will see.
Street trees that are planted in 3X10 tree pits receive the most benefit from mulching the entire 30sqft area.
“How thick of a mulch layer should I apply?”
Mulch wide, not deep, and do not allow mulch to touch the trunk of the tree.
It is extremely important NOT to volcano mulch! Mulch a wide ring in the shape of a donut, and do not pile the mulch up against the trunk of the tree. Most mulch is comprised of decomposing wood chips. The organisms breaking down those chips don’t know the difference between the mulch and the tree, so theycan lead to decay in the tree itself if the mulch is in contact with the trunk/root flare.
Also, applying an excessively thick layer of mulch can limit oxygen in the soil and suffocate the tree!
“What kind of material should I use?”
Tree Pittsburgh uses strictly hardwood mulch. This is a local product made up of old trees, wood pallets, saw mill waste and other ‘recycled’ wood that has been chipped up into small pieces. This material breaks down at a good pace and stays put when applied in tree pits. Pine bark mulch is great, but tends to wash out of tree pits too easily.
We do not recommend cypress or rubber mulch!
Cypress mulch is not a sustainable product and should be avoided. Cypress trees are removed from around the Gulf of Mexico, and hurricane prone areas suffer greater damage in storms as each one is removed.
Rubber mulch does not provide many of the benefits mentioned above. It will not decompose and will remain mixed with the soil for many, many years. There is speculation that rubber mulch may absorb heat and cause damage to the tree.
Thanks to Tirzah Griffin for the mulch and tree planting photography!