Soil - planting trees | Orange County Master Gardener Volunteers

2–3 minute read

The current recommendation is to not amend soil with organic matter when planting trees. The roots must ultimately grow in native soil and amending the planting hole can retard this process. Because of this, the most important part of planting a tree is choosing a tree that is adapted to your site and soil conditions.

Potted

potted

B & B

b&b Bachman’s Landscaping

Soil prep

Loosen the soil by digging or tilling an area 3–5 times the diameter but slightly shallower than the root ball height — 4″ shallower for potted trees, 8″ shallower for balled-and-burlapped (B&B) trees. This compensates for any subsequent settling. To avoid water penetration problems due to the texture interface between the root ball and the native soil, the root ball must be visible at the surface, not covered with any backfill soil.

Root ball prep

If potted, gently press on the container to remove the tree or use a sharp knife to cut away the pot.

Recent research from the University of Minnesota suggests that no technique to stimulate root growth outside of the original root ball is effective in good soil — the number and size of roots emanating from the root ball is roughly the same if the root ball is planted without modification, teased so that roots face outward, sliced on the sides and bottom, or box-cut (cut with a pruning saw into the shape of a box). These results may differ when trees are planted in clay, which was not tested.

Box-cutting destroys more of the root system and retarded growth for a few years, but was the most effective method for preventing circling roots. The preliminary recommendation is to cut girdling and circling roots thicker than a pencil, and either do nothing or box-cut the root ball. The most important step, again, is to expose the root flare. This prevents any circling roots from eventually strangling the trunk.

box cut WA CES Harvesting an experiment

If B&B, once the tree is placed and straight, cut ropes from around the trunk and from the top of the basket. Remove the top of th wire basket if it will be exposed above ground. Remove burlap from the top of the ball so that none will show above the native soil level. Otherwise, the burlap will form a wick that draws water out of the soil and away from the tree roots.

Planting

Place the plant, confirming that the root ball is at the correct height and the plant is straight.
Backfill with native soil, tamping gently with your hand or watering to settle the fill periodically.
Create a shallow berm around the amended soil so that applied water will be retained in the prepared soil. This berm can be removed once the plant is established.
Mulch the ball and surrounding soil, leaving a few inches bare around the tree trunk to discourage voles and to prevent bark rot. A 3–4″ layer of mulch benefits the soil in many ways:
- Keeps the soil surface from eroding
- Prevents disease organisms from splashing onto leaves & flowers
- Keeps roots cool
- Conserves soil moisture
- Keeps the soil surface from crusting & preventing water penetration
- Reduces weed germination
- Supplies organic material & nutrients as it decays
- Provides an attractive finish

top ↑