Beating Heat Stress

We are at the peak of summer, and the weather can have a toll on your trees, shrubs and lawn. Extended periods of heat and humidity, along with bright sunshine, warm nights and inadequate rain can lead to summer stress on your landscape.

soaker-hose
Arranging a soaker hose to cover the critical root zone of a tree is a great method for the slow, saturated watering that’s best for trees.

Horticulturally speaking, the first place many people notice the effects of heat stress is on lawns, which have the good sense to go dormant and wait it out. We definitely recommend a combination of over-seeding and core aeration this fall to help rejuvenate your grass as the summer comes to an end. However, lawns are actually faring better than many trees, although the symptoms may not be as obvious.

Plants are constantly losing water through tiny holes in their leaves through a process called transpiration, and when it’s hot, the rate of that water loss increases. Add to that a lack of adequate rainfall, and the result is often stressed plant material. The problem facing trees is that they’re really big, and they do not have the luxury of going dormant in hot summer months, like lawns. Instead, trees have a lot of active leaves, so they lose a lot of water, and their roots are searching to replace that water in some pretty dry ground.

Trees suffering from heat stress face problems with producing new growth, healing wounds, and fighting against diseases and insects. If they’re stressed enough, they eventually run out of energy to support their existing growth and begin to decline (sometimes irreversibly). Newly planted (within the last 2 years) and mature trees are the most at risk for serious decline, and we’ve seen both this summer. Some trees that are most prone to heat stress and drought include Birches, American Dogwoods, and Japanese Maples.

dried-leaf

Signs of heat stress in trees tend to develop toward the top of the canopy first, so property owners don’t often notice it right away. They include smaller leaf size, leaf scorch (browning and/or yellowing), wilting, and sometimes loss of foliage (a particularly bad sign). 

 

So, What’s the Solution?

The best way to fight heat stress in trees is through a combination of proper irrigation, mulching, and organic soil amendments.

Irrigation:

Proper irrigation means focusing water on saturating the root zone of a tree. Sprinklers may be good for lawns, but they aren’t going to get the job done for trees. A properly placed soaker hose is a better solution. Treegators are ideal especially for young trees, which run a high risk of suffering heat stress. With a traditional garden hose, it’s also possible to set the flow to a trickle and move the mouth of the hose around to four or five different areas of the root zone over the course of the day.

treegators
Treegators are bags with tiny holes that slowly release water into the root zone of a tree.
Mulch:

A good line of defense against hot weather conditions is to apply a layer of mulch around trees and plants. Light colored mulches are better at reflecting sunlight and keeping the soil cooler in summer. Mulch also reduces evaporation of water from the soil and reduces the need to water constantly. However, to be effective, mulch needs to be applied correctly.

mulch

We recommend a depth of 2-3 inches of mulch for trees and shrubs. It should also cover a diameter of 3-4 feet around trees (to the tree’s drip line ideally) and not pile up against the stem or trunk flare. If you have any questions about mulching, please speak to your Almstead arborist.

Soil Care:

In terms of soil care, organic amendments increase a tree’s drought tolerance without spurring new growth that it can’t afford to support (which is the result of synthetic fertilization of heat stressed plants). Also, by using a soil needle injection method for applying soil amendments (as opposed to a soil drench), we can break up compacted ground and introduce better flow of nutrients, air, and water into the root zone. In addition to Almstead’s organic soil care services our arborists are always glad to advise you on irrigation practices, and we also provide watering services for plants out of reach of irrigation.

To formulate a heat stress survival plan for your trees (and shrubs, and lawn), please schedule a complimentary consultation with your Almstead arborist.