March 2024 Treecologist Tribune

The growing season is fully upon us! Tree sap is rising, insects are emerging, and life is on the move. Rainfall since the last Treecologist Tribune has been reasonably ideal—we have had approximately 10 rain events over the past month totaling close to 4 inches, which is good in terms of both distribution and amount. Would more have been better for our local trees? Of course. In terms of temperatures, we have already exceeded 80°F on numerous occasions. From the suburban tree perspective, high temperatures equate to water loss, which generally equates to stress.

In years past, we would list various “pests” that are emerging right now, but I’m beginning to dislike both this term and the concept. We label some insects and fungi as “pests” and view them negatively because they interfere with one of our unnatural landscape systems. For the sake of conventional communication, I will continue to use “pest” here. But there is nothing inherently wrong with them, and they don’t truly deserve this label.

With a few exceptions, most pest issues are a symptom of a suburban wasteland, like plants growing in dirt instead of soil, lack of species diversity, and chemical overuse. Trees growing in these conditions are stressed and emit all sorts of chemical signals that attract pests from miles away. It’s little wonder that hungry insects come to munch on our plants.

The key to preventing these attacks is to foster healthy ecosystems. When we have an abundance and diversity of native plants humming with life, the very idea of a “pest” nearly ceases to make sense—these are now insects and fungi participating in natural ecosystems. The main exceptions to this concept are invasive insects, like the Emerald Ash Borer. These invasive insects have few constraints to stop them, if any.

So, rather than listing all the usual insects that cause damage and how to stop them, let’s focus on the underlying issue. What are things we can do during this season to help foster healthy ecosystems and eliminate the concept of “pests” altogether?

• Build healthy soil.
• Create beds of arborist wood chips around our trees and shrubs.
• Pile thick layers of fallen and rotting leaves in these beds.
• Add lots of compost and compost teas to these beds.
• Skip the usual fertilizers, whether from a nursery or a lawn/tree care provider.
• Avoid the harmful mosquito sprays, something I discussed last month.
• Avoid all the “cides”—pesticides, miticides, fungicides, and so forth. These only make things worse.
• If a plant really needs help withstanding an insect attack, use healthier alternatives like neem oil.
• Here is a fun checklist we made that you can use that includes some other ideas.

These are all things Leaf & Limb can help you with if you don’t have time. If you do have time but want more information, we have many helpful articles on our website and videos on YouTube that you can learn from. We also have our new book, From Wasteland to Wonder, which covers all these topics and more. If you'd like to learn more, you can order it now!

In the spirit of the suggestions listed above, I want to answer these two questions from readers:

1. Tina asks, “You talk about the importance of mulching around tree beds. I have heard that you should not get the mulch too close to the base of the tree. Could you explain how to best mulch around a tree?
2. Susan writes, “I was wondering if ground cover around trees affects the health of a tree or interferes with its ability to get water? For example, I have a Coral Bark Maple that is surrounded by a sedum. The sedum is very healthy and dense and I am concerned it may not allow rain to get to the tree.”

Great questions! When we place mulches (preferably arborist wood chips) around our trees, the key is to avoid placing them on the trunk. This will create a mulch volcano, which is harmful to trees. Here is a helpful video we made about mulch volcanoes.

In terms of the effects of ground cover, this is more nuanced. In general, more plant diversity is desirable. But if those plants begin holding a lot of moisture on the tree trunk or if they prevent water from reaching the roots, they could become problematic. To keep it simple, I usually suggest having a lot of understory plants around your trees—smaller trees, shrubs, flowers, and grasses (all native, of course!). The benefits typically outweigh any possible issues.

Please keep sending me your questions! I love answering them. I have received a number of questions about attracting flireflies, lizards, etc., and I’m hoping to address this topic next month.

Before I go, I want to throw in one more concept you should be thinking about during this season: for trees, health is not the only thing that matters—we also need to think about structural stability. A tree can live in the deepest, healthiest soil in the world but still be split apart in a windstorm if it has poor structure. Now is the time to begin planning annual structural pruning for your trees for later in the year.

Soon enough we’ll hear cicadas singing in the afternoon, see bats flitting about at dusk, and watch fireflies emerging with the stars—I can’t wait!