Pruning Times 101 - Ornamental/Deciduous Trees

Over the years we have noticed a debate that has become common among landscape designers and landscapers. When is the appropriate time to prune? The answer can vary from plant to plant, but there are some general rules for certain groups of plants. The best time to prune trees that flower in the Summer (ex: Koelreuteria paniculata) and Fall (ex: Hamamelis virginiana) is during the late-Winter to early-Spring (typically the month of March in Massachusetts and RI). There will be people that disagree with this phyllosophy, but it's ultimately incorrect or misguided. There are trees that bloom in the Spring (ex: Ornamental Cherry Trees)which should be pruned in the late-Winter to early-Spring as well. Crabapple Trees bloom in the Spring, but begin to set their flower buds for the flowing year during mid-June to early-July. If you prune a Crabapple Tree after early-June you risk reducing the amount of buds/flowers for the following year. It's not the end of the world if you prune it after this time period, but the tree will look more beautiful in the Spring if you don't. Crabapple Trees in particular require hardly any pruning all, except to thin out the interior branches of the tree, so it's less dense and allows more air circulation (this helps reduce rot and disease susceptibility). When trees are pruned in the late-Winter to early-Spring, in some instances such as with Ornamental Cherry Trees the amount of new growth can be denser and more profound.

Other reasons to prune during the late-Winter to early-Spring:

1) Trees and shrubs can get be damaged by heavy wet snow and ice. Pruning may be required to ensure plants stay healthy and in good condition. Broken branches should be pruned as soon as possible. Leaving broken and split branches hanging is like leaving a wound open on your skin. Guess what can happen? Infection! Plants with wounds are more susceptible to disease and insects if they are not pruned properly or in a timely manner when they are damaged.

2) We plead the case that conditions are less favorable for recently pruned plants to become diseased or attacked by insects. When you prune a plant, you're creating new wounds/openings into a plant. It takes time for the plant to heal the wounds (similar to how our own cuts in our skin heal), so the conditions in which pruning is done can also be important.

-In Sudbury, MA (according to weather.com)November is the wettest month of the year with and average precipitation rate of 4.45 inches of rain/melted snow (4.03 in October). March is wet as well (with 3.94 inches), but it's still slightly less than October and November.

-There is less sunlight in November than March (Nov 50% and March 57%).

-Temeratures are warming and stay above the freezing point (32 degrees) more often. November has a higher average temperature range (November 33°F - 52°F and March 28°F - 47°F) and a higher average level of humidity (November 71% in morning - 53% in afternoon and March 66% in morning - 46% in afternoon). Many diseases and insects like warmer temperatures and humidity (moisture in the air).

-Freezing temperatures, especially at night, are more prevalent in March and when combined with all the factors listed above, make plant less susceptible to disease and insects when they are pruned (less likely to become "infected" - in simple terms).

-Less harmful insects around during late-Winter (freezing temps).

3) Autumn is the time of year where things are dying and decaying. Mold spores and other spores are out in the air. Anyone who has allergies during this time of year will understand what I'm talking about. It's not the greatest environment for both plants as well as humans.

4) In the Autumn, plants are going dormant. Deciduous Trees are storing food/energy in their branches, trunk and roots in preparation for the winter. If you prune the branches of deciduous trees in Autumn, you risk reducing the amount of nutrients a plant will have available to survive the winter. Most of the time the tree will survive, but it doesn't help it's overall growth or health over the years.

You can prune trees in the Autumn. It's just better that you do it in the late-Winter to early-Spring (typically March).