The University of Arizona Cooperative Extension has released a new planting standard bulletin, AZ1022, dated 5/98. Studies have shown that tree and shrub roots lie within the top two to three feet of soil and extend one and a half to four times the width of the crown. Steps taken during planting to encourage the growth of these roots can reduce establishment time and help improve its long-term survival and stability. The complete bulletin can be found on the web at http://ag.arizona.edu/pubs/

Here are some notable changes. New Standard: Mark a circular area three to five times the diameter of the root ball. Till or loosen this area to a depth no deeper than the root ball. Walls of the undisturbed soil should be rough and sloping. Dig the hole in the center of the tilled area slightly wider and no deeper than the root ball. A one gallon container will need an area tilled to the width of 2.5 feet, a five gallon container tilled width area will be 4.5 feet and a fifteen gallon will be 7.5 feet.

Old Method: Planting holes were dug out deeper than the root ball. Often the loosened soil at the bottom of the hole packed down after planting, the tree sank down thus promoting crown rot.

New Standard: Refill the planting hole with the soil removed from the hole. Do not use or add organic amendments such as manure, compost, or wood chips. These amendments do not improve, and may even worsen, the growth of the plant. Do not pack the soil. Water the plant in. This will remove any air holes without compacting the soil. More soil may need to be added after the first irrigation.

Old Method: Organic material was added to the backfill. Research now shows that the plant often will not grow beyond the amended soil area but instead will wrap its roots around and around itself. This creates an unstable tree that may require unnecessary staking and is prone to blow over in bad weather.

New Standard: Recent research shows that trees that can sway in the wind form stronger trunks. Stake trees only if they cannot stand without support or threatened by wind, frost heaving, or similar problems. Remove stakes as soon as possible, generally within a year. The bulletin gives excellent guidelines on how to properly stake a tree.

Old Method: Trees were always staked so they could not move and left staked for many years. Often the tree was girdled by the ties that secured the plant when it was young.

Poor drainage can cause problems because roots can drown if they stay too wet for too long. Test drain age by digging a hole about a foot deep and filling it complete y with water twice during the day. Drainage is considered poor if water is still standing 24 hours after the second filling. If the results point to poor drainage, chimney holes may help or consider another area that passes the drainage test.

Now that you've saved money by not using amendments to the back fill, use it to buy mulch. Mulch is often overlooked in the planting process. Mulches are laid on top of the soil surrounding the plant to the depth of three to four inches (do not place against the trunk as this could promote rot) out to the drip line, the area where the rainwater drops off the leaves to the ground. Suitable mulches include ground bark, weed chips, compost, sand, and gravel rocks.