Tree Talk: Trees, Water and Weeds

As drought conditions continue to spread across the country and across the state, the lack of water expresses itself through plants. Trees respond to short-term drought by wilting, leaf scorch and leaf drop. Long-term damage from drought happens over a period of years and includes stunted growth, branch dieback, and possible death of the plant. Many woody plants can take up to three years after a drought to display negative long-term effects.

Pest problems are another result of long-term drought. Healthy trees are able to ward off pests like wood borers and bark beetles. As trees or shrubs become weakened from drought, these pests invade rapidly. (Note: Emerald Ash borer is an exception to this rule. ALL ash trees in North Dakota, whether healthy or stressed, are susceptible to attack from the beetle. To date, EAB has NOT been detected in North Dakota)

Some pests, like sap-sucking spider mites and aphids, can also be more detrimental to their hosts during extended hot and dry periods. The increased injury is a result of the plant’s inability to grow faster than the rate of damage, due to the shortage of water. In addition, many beneficial insects, such as predatory mites, slow or cease foraging activity under drought conditions.

While we cannot control the occurrence or extent of a drought, choosing the right plants for your location and caring for them properly are the best ways to lessen the long-term impact of a drought.

Here are some additional ways to help trees weather a dry spell:

• Incorporate organic matter into the soil. Organic matter builds a healthier soil and enables available moisture to be more accessible to plants.

• Weed regularly. Weeds aggressively compete for space, water and nutrients, and the safest way to eliminate weeds is to pull them out by the roots. Limit the use of herbicides, as they may have adverse effects on non-target plants, including trees.

• Learn to tolerate some weeds. Dandelions and clover provide great pollinator habitat!

• Water. For established trees, watering infrequently but deeply is best. Move the hose to saturate the soil beneath the entire dripline of the tree, every 14 days if there is no rain. For newly planted trees, water weekly with at least five gallons per inch of trunk diameter.

• Do not fertilize during an extended drought. This pulls water from the tree and forces the tree to expend energy to process the fertilizer.

• Mulch. Apply organic mulch like wood chips around the base of trees, using the 3-3-3 formula: keep the mulch 3” away from the trunk, no more than 3” thick, and spread it at least 3’ wide. Mulch helps retain soil moisture, slows down weeds and keeps mowers away from the tree trunk.

Even after it starts to rain regularly again, trees can still suffer from problems related to prolonged drought. Trees are resilient and most will sustain the extended drought of 2021.

For more info: Dakota Gardener: June 2021 - Your Neck of the Woods — Extension and Ag Research News (ndsu.edu)

This is an excerpt from the article “Trees, Water and Weeds”, which was published in CITYScan, August 2021