Proper mulching of the soils surrounding the tree is an important component of tree care. Photo: V. Cotrone, Penn State
Hopefully the right species of tree was selected to match the site and its conditions, next a high quality tree was purchased and it was planted properly (not too deep), before it got too hot this spring. If this is the case, all that is needed is a little bit of after-care.
New Tree--New Root System
Consider that when we transplant a tree, we typically leave quite a bit of the tree's root system behind in the nursery. When balled and burlapped trees are dug with a tree spade and packaged in a rootball, approximately 90% of the tree's root system is removed. With a bare root tree, it might contain more fibrous roots, but it still lost enough roots to cause major stress and mortality in the first year or two. Unlike balled and burlapped or bare root trees, container grown trees have all of their roots, but are grown in soil-less media that dries out quickly. Cutting some of the container grown tree's roots is often necessary to remove girdling roots, as well promoting new root growth that will move into surrounding soils.
So if a newly planted tree has fewer roots, what does it need in order to grow a new root system and become established in its new landscape? Years ago, many recommendations included pruning the top of the tree to compensate for root losses. Thanks to research in the past 20-30 years, it was discovered that compensatory pruning did more harm than good for the tree. Cutting off terminal buds removed a growth hormone called auxin that initiated root growth in the spring. Pruning also removed foliage that the tree needed to produce food (photosynthates) and grow a new root system.
Your New Trees Need Water!
So, what is it that newly planted trees need? Is it fertilizer? Is it a bio-stimulant or mycorrhizae inoculation? No. The new tree needs water on a regular schedule to support the leafy crown that does the work of making food. If you are planting trees and relying on Mother Nature to provide enough rainfall, you might want to re-think that because your trees might not survive very long. Let's put it this way, you spent good money (yes grant funding counts) on trees, worked hard to plant them (sweat equity in the project) and by not making the time to water them each week your trees might just become stressed, and die before they ever get a chance to provide you shade and other benefits.
Research at the Morton Arboretum in Chicago has demonstrated that the soils around the root system (e.g. rootball) dry out every 4-5 days during the summer growing season. Most current recommendations call for providing 10 gallons each week through a slow, deep soaking of the soils surrounding the root system or rootball. Even if a quarter inch rain falls, it will not soak the root system, so developing a program or schedule for watering is critical. If you choose to use a watering device, bag or "gator" that slowly percolates into the soils, remember that rainfall will not fill these devices and someone with a hose and source of water will have to fill them each and every week during the growing season.
Watering devices such as gator bags work well to provide a slow, deep watering. They must be filled weekly by hose because rainfall will not fill the bags! Photo: V. Cotrone
Watering one tree each week at your home is pretty easy, but if your municipality or community organization just planted 75 trees (or even 25), a program needs to be developed to provide them about 10 gallons of water. Some communities use 5 gallon jugs or buckets and a pickup truck to water trees, while others use a large plastic tank or water buffalo fitted with hoses and marine pumps. Some communities utilize volunteers, DPW staff, or even volunteer fire companies that assist with watering community trees. Whatever your organization develops is fine, as long as the trees receive a weekly watering and someone is making sure it happens whether it rains or not.
This 250 gallon water tank that fits in the bed of small pick-up truck, and is perfect for driving around town watering street trees. Photo: V. Cotrone
Mulching, Pruning, and Fertilizing
Another important component of young tree care is proper mulching of the soils surrounding the tree. A natural wood chip mulch will help conserve soil moisture, prevent temperature extremes, reduce competition from grass and weeds, reduce soil compaction, and add organic matter to soils over time. Make sure the mulch is not piled up on the trunk (the flare or taper at the base of tree should be visible) and no deeper than 3-4 inches. It is better to spread the mulch out under the tree's canopy or to the dripline (tips of the branches) than to pile it up thick against the trunk, which creates an environment for opportunistic root rots and diseases to infect the tree. Reapply a fresh, thin layer of mulch every 3 years, not every year.
Over-mulching can cause root rots and other health problems for trees. Photo: V. Cotrone
So when should we consider pruning or fertilizing our newly planted trees? It is best to give the tree a year or two to become established (meaning grow new roots into the surrounding soils) before we fertilize or prune it (because they stimulate new leaf growth). Pruning dead or broken branches, making proper cuts back to branch collars is fine and will not harm the tree, but remember we don't want to diminish the young trees ability to produce food needed to grow a new root system. Once the tree is established, it will be important to begin training pruning to develop good form, structure and strength in the tree.
I believe it was the famous Philadelphian that coined the axiom that "an ounce of prevention is worth a pound of cure", originally discussing home fire prevention, but it certainly applies to developing an after-care program or watering schedule for your newly planted trees, instead of spending more money and time replacing dead trees that you thought would be fine on their own.