Shady Business

Paul Hetzler, Cornell Cooperative Extension of St. Lawrence County

Sometimes it’s good to have a few burly associates for protection, because when the heat’s on and you need to lie low for a while, you can always turn to those shady friends for relief. You know the ones I’m talking about—those big guys with solid builds that no one pushes around. Yeah, the trees. They’re cool.

When the thermometer hits eighty and keeps climbing, any shade is welcome. If you’re lucky enough to have mature trees where you live, not only can you get a break from the sun, but the air temperature will be five to ten degrees cooler than out in the open, natural air conditioning.

Speaking of which, if you use an air conditioner, having shade trees on the south and west sides of your home will reduce your cooling costs by at least thirty percent, and possibly as much as fifty percent. It’s like getting an electric-bill rebate except you save the stamp. Deciduous trees are ideal because they shield you in summer but allow sunlight through in winter when you want it.

On those blistering summer days when you think it’s too hot to work outside, you’re not alone— trees share your outlook. Photosynthesis, that remarkable process that turns carbon dioxide and sunlight into sugar (thereby keeping the trees alive) and oxygen (thereby keeping us alive), actually shuts down above eighty-five degrees. All that solar energy going to waste! Incidentally, leaves can get that hot in the full sun even when the air temperature is cooler, kind of like how a roof gets scorching in the sun.

This is why the inner canopy is essential. Far from being unlucky residents of a less-desirable neighborhood, leaves that are shaded and cooled by the upper canopy are key players in a tree’s survival, as they’re the only ones on the job when it’s too hot for their upstairs neighbors to work. So it’s best not to get overly enthusiastic with pruning. Trees don’t want their inner canopy “cleaned out.” 

Hopefully you’re drinking plenty of water in the summer heat. It might surprise you that trees can run short of water. While we tend to think tree roots dive deep in search of a cool drink, ninety percent of tree roots are in the top ten inches of soil, and ninety-eight percent are in the top eighteen inches.

Lawns recover from severe water shortage in a matter of weeks. Trees, however, take years. Drought stress weakens a tree, making it more vulnerable to diseases and insects. While many shady characters don’t take well to a good soaking, your tree will appreciate a thorough weekly drench.

Here’s to a healthy, hydrated summer on the shady side of town for you and your associates.

Thanks to Michael Greer of Potsdam for suggesting the topic.