Dormant Oil: Spring Prep for Your Trees and Shrubs

It’s that time of year again, winter will soon be coming to an end and Spring will finally free us from Winter’s icy grasp. Winter can be a very stressful time on your trees and shrubs. The freezing temperatures, loads of snow, salt spray, and the moisture-leeching wind, just to name a few. One problem that we don’t think about in the winter, especially for our trees and shrubs, is insects. Your dormant trees and shrubs could be loaded with time bombs right now. Insects overwinter on and in the bark of trees and shrubs, waiting for the temperatures to rise so they can wake from their slumber. So, how can we stop this oncoming invasion? The answer is dormant oil.

What is Dormant Oil?

Dormant Oil is a spray that is applied to the bark of trees and shrubs. This oil will completely cover any of overwintering insects, and their eggs, that may be lying in wait for the warmth of Spring. Once the dormant oil is sprayed onto your trees and shrubs it will create a barrier, cutting off the air supply of all those potentially devastating pests and eliminating them before they can pose a threat.

When Should I Apply Dormant Oil?

Applying dormant oil to your trees and shrubs should only be done at two times of the year:

  • Late Fall: As the temperatures drop and all of the Summer and Fall insects look for a place to lay their eggs and overwinter.
  • Early Spring: Just as the temperatures begin to rise above freezing, before the overwintering insects and their eggs begin to stir.

If you apply dormant oil to your trees and shrubs in the late fall, while you’re taking care of your Fall lawn care, you will be ensuring your trees are well protected from insects as they look for a place to overwinter. This means that in the Spring you will have far less to worry about. Having another application of dormant oil in the early Spring ensures that any of the overwintering insects that you may have missed will be eliminated now. When Spring finally arrives, waking your trees and shrubs come from their Winter dormancy, they will not be burdened by insects. Your healthy trees will be free to grow as much as they can.

Not all trees benefit from dormant oil. In fact, some trees are harmed by dormant oil.

Don’t apply dormant oil to these types of trees:

  • Beech
  • Maples
  • Blue Spruce
  • Douglas Fir
  • Hickory
  • Black Walnut
  • Or any others that are listed on the label

What Pests Are Overwintering On My Trees And Shrubs?

Scale Insects

These little bugs are tough. There are many different types of Scales but they ultimately fall into two categories: Armored Scales and Soft Scales. No matter what type they are, you don’t want these little bugs on your trees. Scales will settle onto the bark of your trees and shrubs and then suck the sap right out of it. If you have a large infestation this can be devastating. Scales rob your trees and shrubs of nutrients and some of them leave behind a waste product called honeydew which is food for a fungus called “sooty mold” which can spread throughout your trees, shrubs, and even onto your sidewalks and patios!

Scales are difficult to spot. Check the bark of your trees and shrubs for small, scale-like bumps. A well-timed application of Dormant Oil will cut off the air supply of these pests, eliminating them before their eggs can hatch in the Spring.


Mites are tiny arachnids, like Spiders and Ticks, that make their home on trees, shrubs, and other plants. Spider Mites are some of the most common pests in the country. Mites cause damage by sucking the chlorophyll out of the leaves of your trees, shrubs, and plants. The damage is first seen as tiny white dots on the leaf but, as the number of these pests grow, can lead to the yellowing of leaves and eventual leaf die off.

Some signs that you might have a Mite infestation include yellow and curling leaves as well as webs in your trees and shrubs. A Dormant Oil application will help you avoid a mite problem altogether by eliminating these overwintering pests before they become active.


Aphids, or plant lice, are tiny bugs that feed on the liquid inside stems and leaves. They use their long, tube-like mouth part to suck the sap out of leaves and stems, injecting their saliva into the plant. This will weaken your plant while also spreading disease. If you have an infestation of aphids, it can do some major damage to your trees, shrubs, and plants.

Caterpillar Eggs

Have you seen large, tent-like webs adorning the trees in your yard? If so, you have a Tent Caterpillar problem. Tent Caterpillars are found all over the country but, here in Maryland, we have the Eastern Tent Caterpillars. When the overwintering eggs of these very hungry Caterpillars hatch, they begin munching away at the leaves of your trees. The massive groups of Caterpillars spin silky tents around leaves, creating a place to protect them at night and during a rainstorm. While a Tent Caterpillar infestation rarely does any permanent damage to trees, their large silk tents and ability to defoliate a tree can leave your ornamentals looking sparse, unhealthy, and ugly.

If you remember seeing the tents from these caterpillars in your trees and shrubs before the Winter, then it’s safe to assume that the eggs from these pests are overwintering on your ornamentals. An application of Dormant Oil in the early Spring will take care of any eggs on your trees and shrubs.

Don’t Want Tree and Shrub Pests? It’s Time to Think About Dormant Oil!

Don’t wait for the pests to stir from their overwintering spots and start damaging your trees and shrubs this fall. The tree and shrub professionals here at On The Green, Inc. have the experience and the know-how to get your trees and shrubs prepared for the spring. We want to help protect your ornamental trees and shrubs from scales, mites, aphids, tent caterpillars, and other destructive pests before they start to wreak havoc on your property. Call On The Green Inc. now for a free quote and ask about our tree and shrub program and dormant oil application. Let’s work together to protect your property.

This entry was posted on Monday, March 11th, 2019 at 8:33 am. Both comments and pings are currently closed.