, Newburyport, MA

March 6, 2013

Tim's Tips: Use warm weather to treat plants

Tim's Tips
Tim Lamprey

---- — Early March is a time when Mother Nature begins to awaken from winter. Maple trees are being tapped and the sugar harvest has begun up north. Slowly, but surely, winter will lose its grip on us. We will probably have a setback or two, but those sunny days are melting the snow that, at first, we all thought would last until May!

The warming days in March will allow you to do some outdoor yard work. One of the most important things you can do is to apply dormant oil to some of your plants.

In the fall, many insects will lay eggs on plants. These eggs hatch out in the spring and the insects attack your plants. In some cases, the insects will crawl into hiding places on the bark of your plants. As the weather warms, they will crawl out of these hiding spots and begin to attack your plants.

Certain plants are prone to insects over-wintering under the bark. These include all fruit trees, including your ornamental fruit trees, grape vines and many of your other fruiting vines. Many of your deciduous shrubs will also offer a home for over-wintering insects and their eggs. Rose bushes are another plant that will be susceptible.

The trick to controlling these insects and their eggs is to use dormant oil on your plants before the insects have a chance to appear. Dormant oil, also called horticultural oil, is applied in late winter when the temperatures are above 40 degrees. The oil is mixed with water and sprayed onto the twigs and branches of your plants.

The oil flows down into all those hiding places and coats the insects and their eggs with a thin film. The oil will suffocate the eggs and the insects. By applying the spray when the temperatures rise, it allows the oil to flow properly and to get down into those hiding places. If the temperatures are too cold, the oil will not flow effectively and you will not get the necessary control to kill those insects and their eggs.

Spraying must be done before the buds begin to swell on the plants. Once tender growth appears on the plants, the oil may damage that new growth. The length of the time frame to perform this spraying depends on what the weather is like during this late part of winter.

As winter slowly drifts away, you have a chance to decrease the number of insects that can damage your plants in the spring. When you get a warm day this month, be sure to apply dormant oil to your deciduous trees and shrubs.

Well, that’s all for this week. I’ll talk to you again next week.


Tim Lamprey is the owner of Harbor Garden Center on Route 1 in Salisbury. His website is Do you have questions for Tim? Send them to, and he will answer them in upcoming columns.