In general, applying fertilizers without a known inadequacy in the soil or tree is not good practice. For this reason, typical fertilizer prescriptions should be made after a soil and/or foliar lab analysis. Our company does not prescribe most fertilizers without confirmation of the tree’s need; however, there are some products that have been shown to be beneficial to trees in known stressful conditions.
The fertilizers and chemicals we carry have been carefully selected as integral components for our plant health care service plans. The products we choose to use are based on personal research, discussions with other arborists, ongoing education, perceived benefit to the trees we care for, and actual experience of success with alleviating tree stress.
Fertilizers and Soil Treatments
Root Invigorator
We stock a very well regarded liquid root fertilizer that is only 2% Nitrogen, 2% Phosphate, and 3% Soluble Potash. It also has smaller quantities of Iron, Manganese, and Zinc which aid in tree green-up and growth, without going overboard. The “magic” of this product is not in the amount of fertilizer, but in the patented blend of humectants that drastically improves soil moisture retention. Application of this product has been proven to promote root development, mitigate drought stress, improve organic activity in poor soils, increase transplant success, and reduce summer as well as winter stress on trees. For best results, applications should be made once every month from spring through fall. If cost is a concern, the hottest summer months are the most beneficial application times for the tree.
Plant Growth Regulator (PGR)
Many trees in urban or residential settings can benefit from treatment with paclobutrazol, a type of PGR which reallocates the tree’s energy from growing longer shoots to other functions such as defense and fine root development. We use a reputable brand of paclobutrazol for trees in close proximity to structures, trees that have sustained rootzone damage, and trees of high value for clients who want the added benefits that often come with treatment:
- Less wasted energy on shoot elongation
- Increased fibrous root development (aiding in drought resistance)
- Altered leaf physiology- thicker cuticles and smaller stomata (less moisture loss in hot weather)
- Increased chlorophyll production of leaves (greener foliage, more food production)
- Shorter internodal spacing gives the appearance of a fuller crown
- Reduced pruning intervals required
The benefits of paclobutrazol in our area can be expected to last 2-3 years, although the effects may not be seen for up to 18 months, depending on tree species, vigor, and timing of application.
Tree Immunity Booster
Although not as frequently recommended as the above two treatments, we do offer an industry-leading product designed to boost immunity levels via a phosphite-based formula with a low salt index. Marketed as a systemic fungicide, this product also provides potassium nutrients and stimulates natural tree defense systems. This product is used to treat a wide array of diseases, but also as a preventative treatment to boost the tree’s immune system. We recommend this product especially to trees that have recently been damaged by construction.
Nutrient-Enriched Soil Backfill
We stock bags of nutrient enriched soil/compost for use as backfill during airspading services (especially radial trenching). In 2025, we submitted a sample of this soil to an independent laboratory to have the nutrient levels tested. Test results came back that it was adequate or optimal in all plant nutrients, both macro and micro.
Biochar Soil Conditioner
Biochar is a highly porous, carbon-based soil additive that does not break down over time (not in our lifetime, at least). This additive drastically increases water and nutrient holding surface area within the soil, improves soil aggregate structure, reduces compaction, and provides a habitat for essential microbes, all of which contribute to improved soil health, and in turn benefit tree rootzones.
Green-Up Booster for Chlorosis or Thin Canopy
Trees that exhibit yellowish or generally thin canopies can be trunk injected in late summer or fall with a specially formulated iron and manganese supplement. This product also blends a handful of other micro nutrients designed to produce a substantial increase of green foliage the following spring.
Insecticides
For healthy trees, insect pests are generally not a concern. Healthy trees usually have sufficient energy for defense against pests on their own, with the exception of invasive pest species (listed below). If a pest is causing problems, it is likely due to pre-existing stressors which have weakened the host tree. A stressed tree will produce a pheromone that actually attracts insect pests. Treating for an insect pest starts with identification and chemical treatment options will be based on the insect species and life cycle. In order to promote education in our communities of WNC, we have briefly described the two most threatening invasive insect pests currently in our area:
Hemlock Woolly Adelgid
Invasive, aphid-like bug from Asia. Attacks and slowly kills untreated Hemlock trees (native, evergreen conifers often mistaken as pines or spruces). The insect is unnoticeable to the naked eye unless ovipositting (white cottony egg sacks). Treat with imidacloprid in spring or fall. For severe infestations, treat with dinotefuran the first year, then follow up with imidacloprid.
Emerald Ash Borer
Invasive metallic green beetle from Asia. Attacks and quickly kills untreated Ash trees (deciduous hardwoods with opposite branching and compound leaves; often very corky bark). The beetle larvae tunnel through the vascular cambium and will kill a mature Ash within a few years of infestation. Multiple trees in the same location are usually focused on one at a time by the borers. Treat with emamectin benzoate via trunk injection for fastest control. Preventative treatments with imidacloprid have also proven to be effective for protection, though not fast acting enough if trees are already infested.
Fungicides and Bacteriacides
As with insect pests, keeping the tree in optimal health will reduce or prevent the presence of disease. There are a myriad of tree diseases, most being fungal and some being bacterial or viruses. Unfortunately for most tree diseases, chemical cures after infection can be difficult or impossible to achieve. If a disease is known to exist in the area, susceptible trees should be protected preventatively to avoid infection.
At Blue Oak, we are always continuing our education on the many tree diseases in our area. We purchase our disease-treatment products from one the leading tree health suppliers in the industry. Furthermore, we use an independent lab to verify disease identity and confirm treatment plans.
The vast majority of trees that have good growing conditions do not develop serious disease problems. Weaker trees provide a better, more vulnerable host to pathogens.
Guidelines to Reduce the Chances of Disease
- Properly prune when tree/shrub canopies are too crowded; this allows light and airflow to penetrate the plant’s interior. Do NOT overprune.
- Perform pruning while diseases are not active (Winter is usually a good choice).
- Do not plant trees too close to each other (especially screening trees). Consider their mature size and plant them at spacing to accommodate it.
- Do not allow trees to become chronically stressed. Avoid acute stressors as well.
- Fix any site conditions that may be causing stress. Compacted soil, buried root flares, and lack of organic mulch around the CRZ are among the most commonly seen.
- Do not allow irrigation systems to wet tree trunks, branches, or leaves.
Interesting fact: diseases generally tend to be host specific (meaning a disease in a tree of one species may not have any affect on a nearby tree of a different species). For this reason, having a variety of tree species is an ideal strategy for reducing catastrophic disease spread in landscapes. Some diseases attack multiple species of trees.
