Shade trees are underestimated friends in hot weather, says local Cooperative Extension forester
Saturday, June 30, 2012 - 6:13 pm


Recent studies indicate that it has been “hot” lately and may in fact be “summer,” with more hot weather to come.

When the heat's on, it's a good idea to turn to your shady associates for relief. You know the ones—those big, burly guys that no one can push around. Yeah, the trees. They’re cool.

When it gets up into the 80s and 90s, 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 around ten degrees cooler than out in the open. The cooler temperature is partly from energy loss due to evaporation and respiration from the leaves (remember Earth Science class?) and partly from the absence of reflected heat from the shaded ground.

If you run an air conditioner, having shade trees on the south and west sides of your home will reduce your cooling costs by at least 30 percent, and possibly as much as 50 percent. It’s like getting a rebate. Deciduous trees are ideal because they allow sunlight in during 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 opinion. Photosynthesis, that remarkable process that turns sunlight into sugar (thereby keeping the trees alive) and oxygen (thereby keeping us alive), actually shuts down when the thermometer tops 85. All that sunshine going to waste! This is when the inner canopy comes in. Far from being unlucky residents of a less-desirable neighborhood, leaves that are shaded (and cooled) by the upper canopy are essential players in a tree’s survival, as they’re the only ones on the job when it’s hot.

Hopefully you’re drinking plenty of water in the summer heat. It might surprise you that trees sometimes run short of water. While we tend to think of tree roots as diving deep in search of water, 90 percent of tree roots are in the top 10 inches of soil, and 98 percent are in the top 18 inches. Lawns recover from severe water shortage in a matter of weeks. Trees take years, and successive droughts can stress a tree to the point that it succumbs to disease or insects. While most 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.

Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.