The Lag Effect of Plant Health Care (PHC) Treatments


If you have ever started a new hobby, you know that generally speaking, you’re not going to be very good at the hobby in the beginning, but if you continue to work at it, you’re going to get better. The same sort of situation happens with trees when we treat them. Generally speaking, the first treatment we give a tree begins the process of correcting tree health, but may not be super noticeable. It’s only after we continue to treat the tree, that we see the best results over time. This is what has come to be known as the “Lag Effect” of PHC treatments, and much like practicing a new hobby, the more you put in, the more you get out.

Where the Lag Effect comes into play is when, as arborists, we are trying to assess a tree’s current health and get the right treatments for the tree. We know that often, it’s going to take multiple treatments over a period of time to see the actual change in the tree we want to see. Now, this does not mean that one treatment is ineffective, it just means that the visual representation of a healthy tree is not always seen until later down the road. Depending on how stressed and how many issues a tree may have, it could easily be 3-5 years before a full recovery is made and the tree shows good signs of thriving. But we have also seen good visual results within one growing season as well. The biggest obstacle, just like treating humans, is that every tree is individual, and every situation is different. There are a lot of variables we cannot measure or know about, and we can only see the top half of the tree, the other 50% is below the ground. We can analyze the soil and the foliage in labs, but at the end of the day, there will always be some trees we just cannot save.

Here is a good example of the difference 4 years made for a very stressed tree. This ash tree had ash borer and chlorosis (a nutrient deficiency). What’s hard to notice from the photos is that the tree in 2019 has about a 15-20% larger canopy with fuller, and thicker leaves.