Soil restructuring is one of the most powerful tools we have for tree health management. The idea is to till the soil; improving its structure will allow valuable air and water to more easily penetrate the soil. While fundamental in gardening theory, this task is not easy at the scale of a large tree.
One of the first challenges we must deal with is maintaining tree roots while tilling the soil. After all, we are trying to help the trees here! This challenge is overcome by use of a tool called an airspade. An airspade is an over powered air compressor that blows away dirt without damaging the tree roots. There is just enough power to displace soil, but not enough to cut through roots.
In most scenarios, we will till the top 4-8” of soil depending on the site conditions. We’ll then add about 2” of finely ground mulch or other organic matter and then re-till the soil to get it all mixed up good. Once this part of the process is completed we’ll top dress it with about 4” of mulch.
The end product is an inviting soil that is great for growing anything. This is as close to mimicking a natural forest floor as we can get in an urban environment. Add a few small to mid size shrubs to provide an additional layer of shade to the soil surface and some irrigation and you’ll have a full blown tree utopia!
There are a variety of ways to apply tree fertilizers and other treatments. For the average layperson, applications to a tree can be challenging. High pressure sprayers are readily available at equipment rental stores, so you can do it yourself, but this equipment is not easy to use. Accessing a tree’s root system deep in the soil or reaching the upper boundaries of canopy on a mature tree requires this special equipment.
Deep root injections are the most common application techniques for tree fertilizing. A pressurized water pump system is used with a “deep-root needle” attached to the end. This needle is inserted into the soil to the desired depth; usually 6-18” deep depending on the site’s soil. The treatments are applied every 2-3′ in a grid pattern throughout the drip-line of the tree. This technique provides a few important benefits. Applications made deep into the soil bypass turf and other small landscape plants root system so competition is reduced. Also, the root needle is about 1” in diameter so everywhere it is inserted a hole is left behind. Soil aeration is an indirect benefit from this application technique.
The next most common application technique for tree treatments is a canopy spray. There are several scenarios when product needs to be applied directly to the foliage. Such as treatment for many foliar fungal diseases, or when we apply our growth hormone treatment to foliage in the spring. Special care must be taken with this application technique. You must make sure the product is not going to be harmful to adjacent plants and the treatment technique should not be done on windy days.
Two techniques for trees that are good for providing direct access to trees systems while maintaining minimal environmental exposure are injections and basal drenches. A trunk injection works much like an I.V. works on you when you go to the hospital. Holes are drilled directly into the tree and a pressurized system delivers the treatment straight into the xylem of the vascular system. Basal drench is just as it sounds. A small concentrated product is poured around the base of the tree and is slow release delivered to the tree over time. By digging a moat before application and covering over when finished, there is very minimal chance of any person or animal being exposed to the treatment.
My hope is that future tree fertilizers and treatments will applied by trunk spray. There is a product out there called Pentra-Bark. Mixed with a treatment products , Pentra-Bark forces the product to absorb through the bark and into the tree’s vascular system. This treatment technique is non destructive to the tree (unlike trunk injections) and provides direct access to the trees system. Using the trees own vascular system to distribute product is very smart. Currently there are no treatments labeled for use with trunk spray technique here in central Texas, but my hope is that this well begin to change soon.
I'm Keith Brown, owner of Austin Tree Experts. This is my repository of tree knowledge. I hope you find what you are looking for. Let me know if you don't.
