What Is The 3-3-3 Rule For Perfectly Smooth And Level Mulch Around Trees?

Not only does a fresh circle of mulch improve the appearance of a tree, but the size and depth of the mulch circle can even have an effect on the health of the plant. The key to a healthy, smooth, and level tree lies in adhering to the 3-3-3 rule, where the mulch is placed three inches deep, three feet away from the trunk in all directions, and with three inches without mulch around the trunk. Since three feet is the radius of the circle, the diameter will then be just over six feet. When viewed from above it will take the form of a six foot diameter donut, not a volcano or a mound.

A mulch circle does more than just make the tree look smooth and level. It retains moisture in the surrounding soil. It also helps control weeds, regulates the temperature of the soil, and protects the tree's trunk from lawnmower or trimmer damage. But be careful. Mulch pressed too closely against the trunk of the tree causes problems such as rotting the bark or pest infestation. 

The 3-3-3 rule does not mean you should apply three additional inches of mulch every year. If there is already mulch applied, measure the overall thickness of the mulch layer and do not use too much mulch — add just enough to replenish it. The International Society of Arboriculture states that three feet is the minimum requirement around any tree but encourages mulching all the way to the drip line of the tree if possible. The drip line of a tree is an imaginary circle on the ground made by the outer edges of the tree's branches and leaves.

To smooth and level the mulch, begin with finding the flare, which is where the trunk starts widening out as it reaches the ground. This part should still be visible. Clear any weeds, grass, or other things within the ring area, and take measurements three feet away from the trunk in multiple locations to create an even circle. A circle of three feet in radius and three inches in depth needs about seven cubic feet of mulch. This is equal to about four two-cubic-foot-bags. Any existing mulch will lower this amount, so it's good to calculate how much mulch you really need to purchase. Create small piles of mulch rather than creating one big pile. Distribute these piles using a rake, moving from outside inwards while leaving the three-inch bare area around the bark. Measure the thickness of the layer with a ruler and move the mulch from the thick spots to the thin spots. 

Keeping the mulch "level" means having the same depth, rather than a perfectly horizontal platform. The mulch should be placed on the yard's existing grade, instead of building up one side or burying the root collar. Rake the area but make sure you do not compact the mulch. To create a more pronounced border, clean the outside edge using a landscape edger without cutting the exposed roots. Monitor the circle of mulch around the tree during wet weather or any activity in your garden and move excess mulch back into the circle, but do not add new layers, unless the old mulch has already decomposed.