Plants are remarkably durable things when you stop to think about it. Humans can only stand so much sun over the course of the day. Too much, and we rush to find shade, or suffer the consequences. By contrast most plants are rooted in place and must weather whatever sunlight falls to them.
For the most part, they hold up far better than we could hope to in the same circumstances, but the height of summer poses special problems. Particularly vulnerable are the roots of plants, which are unaccustomed to the sort of heat the rest of the plant receives above ground. During hot, dry summers, when the sunlight bears full force upon the ground, the temperature of the soil can rise far above its usual placidity, sometimes killing the plants rooted there.
So how do you protect the plants in your landscape when the mercury soars? Below are five general strategies you can adapt to help keep your roots cool.
Keeping your plants watered is essential, but it’s important to make sure that you’re watering properly. A shallow watering that doesn’t penetrate to the roots will mostly result in wasted time and water. Particularly in the heat of summer, deep watering helps by ensuring that plant roots stay nice and cool. To ensure that water is penetrating the soil and reaching the roots where it’s most needed, use a soaker hose or drip irrigation system to water over time, rather than in short bouts. If water costs or municipal restrictions make it difficult to provide adequate water, consider installing a rain barrel to trap natural rain fall for later use.
Reduce unnecessary heat sources
Of course, the sun is the most obvious culprit when it comes to heating the soil, but there might well be other factors involved. You might, for example, have used black plastic in a previous landscaping project, only to find now that it’s trapping heat beneath the soil. Replacing it with a porous landscape fabric will help release the heat otherwise being diverted to the roots of your plants. It’s also possible that the gleaming surfaces of your home are reflecting sunlight onto your landscape. Choosing a less reflective shade of paint for your home, or reducing reflective space with trellised plants, can lower the risk that your home is transferring heat onto your landscape.
Mulch is a multi-purpose ground cover, and one of its many benefits is that it traps moisture, keeping the ground beneath it cool. Not all mulch is created equal, though. For insulating roots against the heat, organic mulches are typically preferred. Stone mulches, by contrast, tend to trap heat. White marble chips in particular can reflect sunlight back up to the plants they surround. That may not be a big deal if you’re using them to dress hot-weather plants like cacti, but over the long term, white marble can cook your more delicate plants, even while they keep the soil cool. For most plants, wood chips are a better choice. You can even create your own mulch by composting your old yard and kitchen trimmings.
Consider this a landscaping solution for a landscaping problem. We’ve already mentioned using creeping plants to dampen the reflective impact of your home, but additional plants can also serve as a more direct source of shade. The more shade you can provide for the ground surrounding plants, the less chance the sun has to warm the soil in which they’re planted. Complement your landscape showpieces with plants that provide more shade. Broadleaf varieties like hosta do a good job of cultivating shade. Ground cover, like sedum or juniper, can also keep the sun at bay. For potted plants, the internal temperature can be lowered by planting a creeping or hanging plant along the perimeter so that its vines or leaves hide the sides of the container.
Build for shade
Plants and mulch aren’t the only way to keep the sun off of our soil. Installing features that increase the amount of shade in your landscape can also help keep roots cool. Lengths of bamboo privacy fence can be used to build screens for extra shade. If you build them on a movable wooden stand, you can store them the rest of the year and only bring them out when the heat’s at its worst. The addition of a well-placed piece of outdoor decor, like a bench or statue, can help increase the amount of shade around the root beds of plants.
Bonus tips for residents of the Southwest
The Southwestern states face their own problems when it comes to keeping roots cool. Plants native to the region have adapted their own strategies for beating the heat. By concentrating on landscaping involving those specially adapted plants, you can avoid many of the problems that might otherwise kill your greenery, but care should be taken to balance their use against water concerns. There are two major types of adaption to look for:
- Xerophytes are plants with physical traits that store water and reduce transpiration, the process whereby water escapes from the surface of the plant. The best known xerophytes are the ubiquitous cactus; succulents are another variety gaining widespread popularity as of late.
- Phreatophytes are plants with especially long root structures. Unlike xerophytes, which have adapted to absorb water when they can get it and store it through the times they can’t, phreatophytes survive by growing next to a stable source of water and using their extra-long roots to maintain a constant connection to the water table. Some of the most successful phreatophytes are the mesquite (which can have roots as long as 80 feet) and the creosote bush.