Tree Planting and Care 101: Soil Management

A tree is impacted just as much by what is below ground as it is by what is above ground.  Trees need water, nutrients, oxygen, and space.  Soil provides the structural foundation of the tree—it keeps the roots rooted and it holds water and nutrients the tree needs to survive. Keeping healthy soil keeps your tree healthy.


Tools
  • Hand cultivator or trowel
  • Shredded bark mulch or wood chips
  • Flowers or bulbs

Guidelines
  • At least once a year, using a hand cultivator, carefully loosen the top 2-3 inches of soil to alleviate compaction and allow water and air to reach the roots. 
  • Make a ring of mulch around the tree, 3-inches deep and as wide as the tree’s canopy. Mulch keeps the water from evaporating quickly, reduces soil compaction, and improves the soil as  the mulch breaks down. It also keeps the soil cooler in summer and warmer in winter. Do not pile the mulch against the trunk of the tree; water will accumulate and rot the trunk. Replenish the mulch at least twice a year, in the spring and fall. 
  • The soil level around a tree should not be changed from the soil level at which it was planted. Adding soil (even a few inches) can smother roots and rot a tree’s trunk. Digging soil out can damage shallow roots. 
  • Keep dogs and dog waste (both liquid and solid) away from the tree. The waste will overwhelm a tree, burning its trunk and throwing soil nutrients out of balance. 
  • Keep garbage and de-icing salt out of the tree pit. Try alternatives to rock salt (sodium chloride) such as calcium chloride, granular urea, sand, or sawdust. In the spring, flush the tree pit with water to dilute winter salt buildup. 
  • For a street tree, consider installing tree pit guards. Strong metal or wooden guards around the edge of the pit protect the soil by discouraging pedestrians and dogs from walking through the pit. Do not place tree guards close to the tree. Do not build solid walls; these encourage people to add soil to the tree pit (see above guideline). We do not recommend tree grates (metal grating that sits flush with the sidewalk) since trash accumulates beneath the grates and trees that outgrow a grate can be fatally girdled or strangled. Get more information on tree pit guards. 
  • As the tree grows, if it’s not in a pit, consider widening the mulch ring to keep it in line with the canopy of the tree. In addition to its many other benefits, mulch protects the tree’s roots from competition with grass, and protects the trunk from lawnmower damage. 
  • A wider mulch ring will also help if it is hard to get grass to grow under the tree. And it may help if grass is growing and the tree isn’t doing well. The grass may be winning over the tree’s roots for moisture and nutrients.