1. Dig a hole
Make sure the hole is twice as wide as and slightly shallower than the root ball. This puts the aerated backfill soil where the new roots will grow and leaves a base of naturally firm soil for the root ball to rest on, which won’t settle when watered. Some cities may require that you use a root barrier to prevent roots from pushing up the sidewalk or a cage to keep gophers out. If this is the case, the size and shape of the device will determine the dimensions of the hole.
2. Avoid the clay-pot syndrome
Roughen the sides and bottom of your planting hole with a pick or shovel so that root tips can penetrate the native soil. Smooth walls are like cement to root tips. *Important: If you are using potted trees, be gentle but firm when removing the container. Making sure to protect the foliage, lay the tree on its side with the container end near the planting hole. Hit the bottom and sides of the container until the root ball is loosened. If the container is metal, use cutters to snip it from top to bottom.
3. Check the root ball for circling roots
If left in place, these roots will continue to enlarge in that pattern after the tree has been planted. Gently separate them, shorten exceptionally long roots, and guide them downward or outward. If roots are severely circled or kinked near the trunk, ask for your money back and get another specimen. Remember that the tiny root tips that absorb water and minerals for the tree die off quickly when exposed to light and air, so don’t waste time.
4. Don’t cover the root crown with soil
The crown is the place where the roots end and the trunk begins. Soil here will lead to rot at the base of the trunk. Aim to have the top of the root ball be about 1/2 to 1 inch above the surrounding soil. Check the height of the root crown by laying a straight piece of wood across the top of the hole. Adjust the height if necessary by lifting the tree by the root ball out of the hole and adjusting the soil level in the planting hole.
5. Orient the tree while you have the chance
If the tree has a preferred side, turn it toward a prominent viewpoint, such as your kitchen window. If it’s lopsided, turn the side with more foliage toward the prevailing wind. This will encourage the other side to catch up. In sunny, arid climates, orient the tree so that the best-shaded side of the trunk faces southwest. Sunburn can kill the cambium, weakening the tree and disfiguring the trunk and bark. When turning the tree, lift it from the base of the root ball, not from the base of the trunk.
6. Sight it upright!
Once the tree is in the hole, stand back and make sure it’s standing upright. Tilt the root ball until the tree is straight, then backfill firmly under and around it.
7. Give your soil a boost
Though the latest trend in tree planting is not to add amendment to the backfill soil, there are instances when it can be useful. If your native soil is hard to work with (heavy clay) or retains little moisture (very sandy), you can treat it to some organic amendment. The amendment won’t be a permanent solution to soil deficiencies, but it will help retain water and air in the soil around the root ball for the first few vital years. If adding soil amendment, always mix it with soil from the planting site; about one part amendment to three parts native soil is a good proportion for backfill soil.
8. Tap the soil as you backfill
Using the heel of your foot, press down firmly to collapse any large air pockets in the soil. This will help stabilize the tree in the hole. Don’t wait until the planting is finished; press down every few shovels of soil. Yes, you can tamp too much; excessive pressure (especially in clay soils) will reduce the soil porosity, which is essential for healthy root growth. As usual with trees (and most living things), practice moderation.
9. Get it wet!
Build a temporary watering basin around the root ball to encourage water penetration. A tree that has a dry root ball can stand in a moist backfill without absorbing water! Fill several times to water deeply. Widen basin to include whole planting area after a month.
10. Stake well!
Remove the square wooden nursery stake after planting. Stake the tree loosely for protection or support if needed. Provide two stakes per tree. If the stem can’t stand up on its own, stake it so that it stands upright. Use non-abrasive ties in figure-eight pattern. Plan to remove stakes as soon as the tree can support itself, in six to twelve months.
11. Mulch ’til you drop!
Cover the entire planting area, except a small circle at the base of the trunk, to a depth of 2 to 4 inches with bark, wood chips, old sawdust, pine needles, leaves, or, if you have none of the above, gravel. Mulch keeps the topsoil temperate for root growth, reduces surface evaporation of water, provides nutrients to feed the tree, and slows weed and grass growth around the tree’s base. It also prevents a hard crust, which slows water penetration, from forming on top of the soil. For plantings along a street or sidewalk, concrete or decomposed granite will act as mulch, but you must allow an open area for air and water exchange.