Newly-planted trees need active and frequent care during the entire establishment period. In USDA hardiness zones 4 and 5, the establishment period lasts about 12 months per inch of trunk diameter. For a two-inch caliper tree, this translates into a 24-month establishment period. Good cultural practices during this period help reduce transplant stress and create a favorable environment for tree growth.
Consistent and proper care during the establishment period is the single most important thing you can do to have success with your new tree.
The key to watering newly planted trees is to check the moisture status of the plant's root ball. The roots of newly planted trees are initially confined to the plant's rootball. Newly planted trees should be watered when the rootball (not the surrounding soil) begins to dry out. Frequently check the moisture status of the rootball as it can dry out quickly.
To water newly-planted trees, slowly apply water to the base of the tree using a hose with a water breaker, soaker hose, or spot sprinkler. A hose turned on to a trickle can be used to reduce water run-off but it's important that the entire root mass is wetted so the trickling hose needs to be moved around to ensure the entire rootball is wet. Tree watering bags or leaky buckets can also be used to reduce run-off while deeply and thoroughly wetting the rootball. Most empty in 2 to 9 hours. Watering bags do not replace the need to regularly check soil moisture nor do they reduce the frequency of watering. They are a convenient way to water the root zone, especially the original root ball. However, as roots grow into the surrounding soil, additional watering techniques will need to be used to wet the entire root zone.
The frequency of watering can be reduced and the watering area enlarged as the tree's root system begins to grow into the surrounding soil. Small trees usually require watering for 1 or 2 growing seasons. It may be necessary to periodically water large trees for 3 or 4 years.
To help conserve moisture, place 2 to 4 inches of mulch, such as wood chips or shredded bark, around trees. Mulches also help control weeds, moderate soil temperatures, and reduce the risk of mechanical damage to tree trunks from errant lawnmowers and string-trimmers.
When mulching trees, do not place mulch against the tree's trunk. Feather mulch up to but not covering the root flare. Ideally, the mulch is only shallowly covering the soil at least 6 inches away from the trunk of the tree. Mulch piled against the tree trunk may create favorable conditions for fungal cankers, root rots, insects, and rodents.
It is generally not necessary to fertilize newly planted trees. Most Iowa soils can supply sufficient amounts of nutrients during establishment. If the trees are growing poorly 2 to 3 years after planting, fertilization may be beneficial. Poorly growing trees often exhibit sparse foliage, yellow-green leaves, or short annual twig growth. in these situations, apply the first application of fertilizer at the beginning of the second growing season.
Trees utilize sugars and other carbohydrates manufactured by the foliage for plant growth. Therefore, avoid the temptation to severely prune newly planted trees. Severe pruning reduces the tree's ability to manufacture food and actually slows plant growth. Newly planted trees require only corrective pruning. Remove structural defects, such as double leaders and dead, broken, or crossing branches.
Retain most of the lower branches to help stabilize the tree. Research shows that these lower branches help improve trunk size and strength. Gradually remove the lower limbs as the tree grows during the first 5 to 10 years until the canopy is at the desired height. Remove lower branches when they are 1 to 2 inches in diameter or less. If lower branches on young trees are in the way of mowing, then remove the grass and mulch the area to keep the mower further away from the tree.
Staking is not required for many newly planted trees. However, bare-root trees, top-heavy trees, and those planted in windy, exposed sites may require staking. If staking is necessary, allow the trunk to move or sway for proper trunk and root development. Drive one or two sturdy metal or wooden stakes with one stake upwind from the prevailing winds in the areas. Position the stake outside of the planting hole in undisturbed soil. To prevent damage to the trunk, use strong, wide strips of canvas, rubber, strips of cotton t-shirts, or other wide flexible materials to support the tree. Do not use rope, twine, or wire (including wire run through a section of old garden hose to act as a "cushion") to support the tree. These materials easily cause abrasion to the stem and can potentially girdle the trunk when left on too long. Remove the stakes as soon as possible. In most cases, stakes can be safely removed after one growing season.
Wrapping protective materials around the trunks of newly planted trees is usually not necessary during the growing season. There is little or no benefit to tree wraps during this time. However, tree wraps are beneficial during the winter months on young trees to prevent rodent damage or sunscald injury. If you do decide to use a tree wrap, place it around the tree in fall (November) and promptly remove it the following spring (April).