Because of the COVID-19 pandemic, I have been doing a large number of digital diangoses this summer. While I have always felt that working with physical samples is the best way to diagnose disease issues, there has been one area where having access to photos has been of great benefit: diagnosing nondisease issues causing general decline and dieback of woody ornamentals, particularly deciduous trees. Seeing so many photos has really educated me in just how many tree issues have nothing to do with diseases, but everything to do with improper plant selection and planting. This month, I would like to share some of what I have learned after seeing this plethora of photos.
Plant the right tree in the right location. Many tree problems that I have diagnosed this summer have to do with use of trees that are not well-adapted to the sites where they are planted. For trees to be successful, I can’t emphasize enough how critical it is that the site conditions (e.g., soil pH, light, temperature, moisture) match with the conditions preferred by the particular tree that is to be grown at the site. I constantly see trees such as pin oaks and red maples planted in locations where the soil pH is too high, leading to problems with chlorosis. Similarly, I see trees like pagoda dogwood (an understory tree that prefers shady, cool, moist condtions) planted in the middle of yards in full sun, with grass growing up to the trunk. The stress from excessive sun and heat, as well as water stress from competition with turf, makes pagoda dogwood prone to golden canker, which can eventually kill the tree.
Start small. People seem to want an instant “finished” landscape filled with mature, full-sized trees. While planting large trees is easy to do (or at least easy to have done professionally), keeping these trees alive after planting is another issue. I can’t tell you how many times I have chatted with folks who have planted large trees, only to have them die. They then replace these trees with other full-sized trees, only to have these replacements die as well. And on and on and on. What people don’t realize is that when a tree is dug at a nursery, a large percentage of its root system (up to 60%) is left behind. This root loss puts a tree under incredible stress. The bigger the tree is, the biggerer the stress and the lower the probability that the tree will survive transplanting. Personally, I don’t like transplanting trees much over four feet tall. I have found that smaller trees survive better. Often by starting small, you can end up with a well-established, large tree in the same time period as transplanting and replacing multiple, full-sized trees.
Prepare transplants properly. Many people end up buying balled and burlaped trees, and a big mistake they make is to not remove the burlap, underlying wire basket and wires/cords/strings on these plants. Burlap and wire baskets do not break down rapidly (as is often the claim) and can interfere with proper root growth. Burlap exposed above ground can wick water away from trees, leading to water stress. Wires, cords and strings can girdle trunks, eventually killing trees.
Plant at the correct depth. I have seen numerous photos of trees that have been planted too deeply. The trunks of these trees look like telephone poles as they enter the ground. Ideally, the root flare (i.e., the part of the trunk that widens to form the roots) should be visible just above the soil line. With many balled and burlaped trees, removing soil from the top of the root ball will be necessary to expose the root flare.
Overly deep planting increases the likelihood of girdling roots. These are roots that instead of growing outward from the trunk, grow around the trunk. If girdling roots form and are left in place, the trunk will eventually come into contact with these roots, and the roots will compress the water-conducting tissue under the trunk’s bark. This will inhibit water movement from the roots into the branches, leading to canopy thinning, branch dieback and tree decline. Stress from girdling roots can also make trees (particularly maples) more prone to frost cracks, the vertical cracks that are often found on the southeast sides of tree trunks. Frost cracks can provide entry points for wood rot fungi that do additional damage and structurally weaken trees, making them more prone to snapping off or blowing over in high winds.
Personally, I like to plant bare-root trees, because I think they are easier to plant properly. I can easily see the root flare (and get it positioned properly), and I can orient roots at planting to prevent formation of girdling roots.
Mulch properly. I often see trees with grass growing right up to the trunk. Grass is very efficient at taking up water and preventing it from getting to trees. I suggest removing turf out to the drip line of a tree (i.e., the edge of where the branches extend) and mulching this area with a high quality mulch (e.g., shredded oak bark mulch or red cedar mulch). Use one to two inches of mulch if you have a heavier (e.g., clay) soil, and three to four inches if you have a lighter (e.g., sandy) soil. Keep the mulch about four inches away from the trunk.
Water, water, water. Homeowners often water new transplants for a few weeks, but then believe the trees are well-established enough that they no longer need to water. In reality, new transplants need LOTS of water for a LONG time. I typically recommend that new transplants (anything planted within roughly the past three years, maybe even long for larger transplants) receive about two inches of water per week from the time they bud out in the spring, through the summer and into the fall up until they start to turn their normal fall color (for deciduous trees) or until the ground freezes or there is a significant snowfall (for evergreens). If Mother Nature doesn’t cooperate, I suggest watering at the drip lines of trees using a drip or soaker hose.
Ask for help. Hopefully, the pointers above will help you successfully transplant trees and keep them healthy and vigorous. If you run into disease problems or other issues as you grow your trees, and need help diagnosing these problems (or problems of any other kind of plant for that matter), feel free to contact the PDDC. For the PDDC’s current policy on sample submission, including submission of digital photos, check out the following link. As always, be sure to check out the PDDC website for timely information on plant diseases. Also, feel free to follow the clinic on Twitter or Facebook (@UWPDDC) to receive timely PDDC updates. Or alternately, put in a request to subscribe to the clinic’s new listserv (UWPDDCLearn) by emailing firstname.lastname@example.org.
Hang in there, be safe, and stay healthy everyone!