Spread a 2 to 4 inch layer of some attractive organic material over the soil in a circle out as far as the drip line of the Oak’s branches. Avoid piling it up against the base of the trunk. This will keep the soil moist and control weeds. Because chopped leaves, pine needles, wood chips or similar materials mixed with peat moss decompose over the season, the mulch will also improve the texture and fertility of the soil under the tree.
Expect to renew the mulch periodically when it is less than 2 inches thick. Be sure to maintain it over the winter to buffer the soil from the effects of freezing and thawing, which disturb shallow tree roots. Maintaining a mulch under your trees will eventually reduce their need for supplemental fertilizer when they are older.
The shallow roots of young Oaks like moist soil. Water young, newly planted trees well over their first year or two while they become established. Once they are established in good soil that contains sufficient organic matter, Oaks will not need additional watering when rainfall is normal and regular. They will need supplementary water only in late fall before the ground freezes for the winter.
If the trees are growing in poor soil, or rainfall levels are low, water Oaks deeply once every 7 to 10 days in the warm season. Run a sprinkler for 20 to 30 minutes at a time or use a sOaker hose system hooked up to mechanical or computerized timer. This is the most effective way to deliver water gradually to trees and shrubs.
Feed young White Oaks once a year in the fall, starting a year after they are planted. Sprinkle an all-purpose slow-acting granular fertilizer on the soil under the tree out to 1 or 1½ feet beyond the tips of the branches (the dripline). Do not allow the fertilizer to touch the tree trunk. If there are no instructions for use on trees on the product label, use 1 cup or so of fertilizer for every inch of trunk diameter.
If trees are planted in good soil and are mulched with organic material such as chopped leaves or shredded bark year round, after the first few years annual fertilizing will not be necessary. The decomposing mulch will contribute nutrients to their soil.
Young trees may need some corrective pruning at the outset. In the late winter before leaves begin to emerge evaluate the shape of the young tree. If it appears to be developing a double main stem, or leader, prune away the weakest or least dominant one. This assures a strong trunk as the tree matures. Take this opportunity to prune branches that cross each other to eliminate abrasions on the tender bark from rubbing.
Oaks do not require routine pruning. Over the years there may be the occasional injured or broken branch. Cut it off cleanly and promptly with a sharp pruning saw, or use loppers for branches an inch or less in diameter. This will promote healing and prevent the invasion of insects or rot into tree tissues. Sometimes it is necessary to prune off lower branches of large trees to allow more light into the yard. For pruning jobs on large trees, hire a professional, certified arborist.
Pruning is only necessary if there has been some storm damage or if some branches start to grow across each other and are touching. Never prune between April and July to minimize access to the tree by Oak wilt.