Drought Stress on Trees
Drought Stress on Trees
Author(s): Justin Evertson
Nebraska landscapes experience a great deal of "climate weirdness." Lack of significant moisture and long-term high temperatures put stress on landscapes. How then do we sustain our landscapes in these unusual circumstances?
Prioritize efforts in the landscape
In terms of environmental, economic and social benefits, landscape priorities tend to run in this order:
- perennials and ornamental grasses
- turf grasses
Let's face it—it’s a lot easier to replace turf than to replant established trees.
- Newly planted trees need supplemental watering to survive. Normally we define “newly planted” as within the last five years to 10 years, given the current extreme drought conditions. Even well-established trees that are 20 years old or older are showing stress.
- Concentrate watering under the tree's canopy for a long enough duration that water is getting beyond the turf-rooting zone to a depth of 8-12” or more.
- Soaker Hoses
- Gator bags (or similar products)
- Root feeders: Efficiently water many trees in a short period of time and direct water at the critical rooting zone 8”-12” below the surface of most soils. By forcing water down into the rooting area, root feeders increase soil oxygen levels and create more favorable growing conditions. This is especially beneficial in high-use areas like parks, where soil compaction is a limiting growth factor.
A cautionary note
All tools and methods have pros and cons. For example, do not use gator bags if you are going to leave them on the trees empty with no water as they will act like little convection ovens on the tree trunk.
Also, while most of these watering systems allow for the incorporation of fertilizers, especially in the case of root feeders, that is the last thing you should do during a time of drought, since adding fertilizer could cause a flush of growth and further stress your plants with higher water demands.
Keep it simple
Mulch/remulch all trees and planting beds to maintain an average 3-4” layer of well-seasoned, aged chips. Mulch helps maintain soil moisture and reduces soil temperature but, most importantly, it keeps mowers and weed whackers away from tree trunks and valued shrubs and perennial beds.
Use “utility grade” chips, which are typically fairly large, thin chips produced from utility clearing operations, as opposed to double ground or grinder chips. Larger chips typically last 1-2 seasons, layer well and do not mat together, allowing good gas exchange between the soil and atmosphere. Low oxygen levels in soil are the most limiting factor for root growth in most urban soils.
Avoid mulch products such as river rock, pea gravel, etc., as they can dramatically increase soil temperatures. Also avoid cypress mulch, as it readily mats together and takes a long time to break down and add to the soil profile.
Most importantly, consider long-term solutions to water conservation practices and landscape management requirements. Within the average life of a public or park landscape, it will typically experience many periods of drought and extreme weather. Observe what works and what does not, and alter your landscape designs, plant selection and management input to take such things as drought into consideration.
Six tips for drought-tolerant landscapes
- Pick the right plants for the landscape – and think native plants! There are many, many drought-tolerant trees, shrubs, perennials and grasses that can be selected. Some of the best are our regionally native plants. Use more of those!
- Don’t scatter trees or landscape plants across a landscape. Instead, plant trees and shrubs together in complementary groups and use them as anchors for additional landscape plantings – including perennials and ornamental grasses. Mulch them in mass and you’ll have a grouping of plants that are much easier to manage and have similar irrigation requirements.
- Mulch around trees and shrubs – and mulch landscape plantings into larger beds separated from turf zones.
- Limit the use of high-input turf grass to where it is truly needed – and begin converting parts of the lawn to more drought-tolerant species. Lawn development and care is a mindset: our vision should not be an emerald green carpet of turf rolling unimpeded across a community, but rather pockets of constant greenness where they make sense – where picnics, sports or other summer activities will happen. Otherwise, plan for most turfgrass areas to be compatible with summer brownness.
- Think healthy soil! The more organic and biodiverse the soil, the more drought tolerant it is. Organic soils better absorb and retain moisture. A healthy landscape begins with healthy soils.
- Design and manage irrigation systems wisely! Irrigation systems can be a good tool for landscape care, but they are also a primary source of significant waste of drinking water. There is no law that says an irrigation system should run every day or every other day. Irrigation systems should be seen as supplemental sources of water, not the primary source of water. We have a LONG way to go in this regard.