Watering and Mulching
Most newly planted trees need an inch of water a week during the first growing season to help their root systems develop. Consequently, when your rain gauge indicates that rainfall is insufficient you need to water. Use a slowly dripping garden hose or a soaker hose system which delivers water efficiently and gradually. Do not overwater; most trees do not like soggy soil. Continue watering regularly until mid-fall and then taper off.
The 3 or 4 inch layer of organic mulch that you spread over the root zone at planting time will gradually decompose in summer heat. Add more periodically to maintain its thickness. Do not pile it up against the tree trunk. The mulch will absorb and retain moisture, reduce run-off in heavy rains, and block evaporation of moisture from the soil.
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Do not fertilize newly planted trees during their first year in place. Most of the top growth a tree puts out in its first year is stimulated by the starches already stored in the tree. Extra fertilizing after planting only encourages leafy growth at a time when root development is more important.
Begin fertilizing in the early spring or late fall a year after the planting date. Sprinkle a balanced, all-purpose slow-acting granular fertilizer, or one formulated for acid loving trees such as hollies and camellias, on the soil or mulch over the root zone of the tree. The rain or watering will soak it in. Keep this area free of grass so that it does not use the nutrients.
Remember, as a tree becomes established and grows larger, its roots spread well beyond its dripline, so you will have to fertilize a wider area. If the package label does not indicate amounts for trees, use ½ pound of fertilizer for each ½ inch of trunk diameter measured 4 feet up from soil level. After 5 or 6 years, if the tree is regularly mulched so that decomposing organic matter keeps its soil fertile, there is no need to fertilize every year.
There is rarely any need to prune a newly planted tree unless a branch is injured or broken during the process. If any branches cross and rub one another, bruising their tender bark, remove one of them. Also remove any suckers, weak new growth sprouting from the trunk or base of the tree. Nursery-produced trees are usually appropriately pruned. The one exception is bare-root trees which may benefit from pruning away some branches to compensate for roots lost when they were prepared for shipping.
After a year or two some corrective structural pruning may be necessary. Sometimes trees develop two leaders, or main stems. With a sharp pruning saw or loppers, cut off the weaker one to encourage the development of a single strong trunk. Use hand pruners if stems or branches are no thicker than your thumb.