Try these 5 tips to help garden survive the scorching heat

Picture of Paul Cappiello Ph.D.

Paul Cappiello Ph.D.

Yew Dell Botanical Gardens Executive Director

Who said it isn’t summer yet?! When you walk out the door first thing in the morning and it feels like you’re wearing a big old bowl of possum stew around your neck, you know the heat and humidity have arrived for the season.

This is a tough time of year for all of us – both for plants and the people who tend them. Sure, we’ve had a little warm weather here and there but a sold week of blistering heat and stupefying humidity tests all of us. And it’s particularly stressful on plants when it comes earlier than normal. 

When the worst of the heat shows up according to a normal schedule (whatever normal is these days!) your container plantings have adequate time to root in and get settled into the season. The annuals you planted in front of the azaleas have spread their roots to harvest water from a wide swath of ground. Newly planted trees and shrubs have started to root out beyond the soft, fluffy backfill. Once plants hit that stage of development they have a lot more room for error in irrigation schedules. They can better handle heat and drying cycles.

But when record hot weather hits plants in June, they’re not quite ready for summer’s worst so you have to pay a bit more attention. Here are a few tips for keeping your plants as happy as possible through a tough stretch of weather.

1- The end of the road for cool season bloomers 

If you’ve been babying your pansies through the tail end of spring, good for you. Unfortunately, this is about the end of the road. Some plants have the ability to deal with high temps consistently in the 90s but pansies aren’t on that list. It’s good to know the limits of those spring specialists so you can avoid tearing our your sweat-drenched hair trying to get those now-pathetic,  last few blooms to last a little longer. Time for a trip to the compost bin!

2- Cool roots make for happy container plants

If you’re like me, you have clusters of nice glazed containers here and there on the driveway, back patio and around the front steps. They’re great to add pops of color here and there without the hassle of digging up an entirely new bed. But life in a ceramic container can be tough. 

For just about all plants we grow in this part of the world, the optimum temperature for root growth is the low to mid 70s. In soil much above 80 degrees, most plant roots shut down. And it’s the actively growing roots that do the most to absorb water and nutrients. A quick look at this past week’s temperatures (mid 70s at night and high 90s during the day) leaves little doubt as to the root zone temperatures inside those containers. Add the dramatically elevated heat in that driveway material and reflected light coming off the surface and it is easy to see container contents rise to temperatures well over 100 degrees!

But there are a few things you can do to help. Irrigation is the best solution for cooling roots. If you’re still working from home, plan to give your plants a shot of water morning, noon and dinner time, whether they need it or not. If you’re at the office all day, hit them in the morning and when you get home again. The cool water will quickly drop the temperature inside that container and let your plants recover a bit. You can also tightly cluster containers so they shade each other for a little thermal relief.

3- Watch out for that hot hose

You get home from work and all your plants are wilted and pathetic looking. Being a concerned and committed gardener you jump out of the car, turn on the spigot and immediately flood your thirsty plants with water. Unfortunately, you failed to appreciate that your hose has been sitting on the baking hot driveway all day long. The water contained in that hose is now the temperature of a cup of McDonalds’s coffee before the lawsuit! Let that hose run for a few minutes until the water runs cool. Your plants will thank you…

4- Mulch with moderation

It’s pretty obvious but a nice, uniform layer of organic mulch put down about 1 to 2 inches thick will do a lot to help even out both the temperature and moisture fluctuations in the soil around your plant’s roots. It won’t help a whole lot in a planted container but trees, shrubs, herbaceous perennials and even annuals planted in the ground will benefit from a light layer of mulch. You’ll be amazed how much of your painstakingly applied water evaporates long before it has a chance to get to plant roots. 

5- The garden’s heat-induced silver lining

While the kind of heat we experienced over the last week can be the end of the road for your spring pansies and put a temporary stop to your tomato blooms, there are actually some plants out there that thrive on the heat. If you planted a few sunflowers from seed this spring, you’ve probably noticed that they’ve grown about a foot in the last 5 days. Sweet corn in the vegetable garden will reach that elephant’s eye a whole lot faster in this kind of heat. One of my favorite annuals for the garden, Persian Shield (Storbilanthes dyerianus) that offers stunning leaves of an almost metallic purple and silver, usually sits around all spring, waiting for the heat. It usually doesn’t do much until around the middle of July. This year… it’s growing like gangbusters.

Beyond all that, pace yourself, drink plenty of water and avoid the possum stew…

This article was originally submitted to the Courier Journal on June 13, 2022.

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