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Green Speak

Horticulture topics from gardens to lawns and then some.

The Resilient Landscape, Preparing Your Plants for Weather-Related Disasters Part 2: Drought


Following is a continuation of my exploration on the aftermath and preparation of weather-related disasters on our landscape plants. You can find the first article on winds HERE.

Drought

In the book Weatherproofing Your Landscape, authors Sandra Dark and Dean Hill classify weather-related disasters as the 'Big Four' – wind, drought, flood, and frozen stuff. As we move from July into August, hot, dry weather commonly becomes an issue in many areas of the Midwest. This makes the topic of drought very timely indeed!

The summer of 2012 saw my first year as an Extension horticulture educator; it also was one of the driest years on record. Illinois saw massive shortages of rainfall that year- complete with water restrictions, loss of crops and the demise of many ornamental landscapes. Needless to say, it was a summer that will be remembered. Then in 2013 we experienced another significant drought. So what are the best practices for getting your landscape plants through a drought? And what can we do to prepare for the next one?

During the Disaster

Due to its slow progression, drought is one of the few weather-related disasters that we can actively work to remediate during the actual weather event. However, drought's nearly benign presence has a nasty habit of sneaking up on homeowners, especially when it comes to our trees.

Indications of drought are fairly easy to distinguish on our herbaceous perennials, annuals and many woody shrubs, as these plants tend to wilt during times of water stress. (FYI, if you are in the heat of summer with plenty of soil moisture and your plants are still wilting, this is likely a natural response to the high temperatures. The leaves should perk back up in the cooler evening hours.) Be mindful of landscape shrubs and small trees like holly that have waxy leaves. These tend not to wilt but simply dry, turn brown and drop. Same goes for our needled evergreens.

Cool season lawns have a survival mechanism that allows them to go dormant during hot, dry weather. Dormant lawn grass is straw-colored in appearance and is a slight deterrence to those who enjoy walking barefoot in the lawn. And what good deterrent it is, because walking on dormant grass risks damaging the growing point at the soil line (a.k.a. the crown) that sends up new leaf blades during active growth. While dormant, your lawn will only need to be watered in the most extreme of droughts. Case-in-point the drought of 2012. After a month of no rainfall, a dormant lawn begins to run the risk of suffering irreversible death of the crowns. In order to keep the crown alive during extreme drought Extension recommends watering ¼- or ½-inch of water every two to four weeks, respectively. That amount of water is enough to keep the crowns alive, but not enough to knock the grass out of dormancy.

During extreme drought communities might face water restrictions; therefore you must prioritize your watering regimen. Lawns can be seeded and regrow within a year, perennials and shrubs can be replaced next season. The big ticket items in our landscapes are our large shade trees. You cannot replace a fifty year old tree without investing another fifty years. Unfortunately, many homeowners don't think to water their mature trees, believing an extensive taproot has made it to some reservoir deep underground. When in fact most trees do not have taproots, with most tree's roots found in the top six- to eighteen-inches of the soil.

When strategizing your watering make sure to give the following plants priority:

  • Recent transplants
  • Specimens that have suffered stress or damage in recent years
  • Trees or shrubs that whose planting location restricts root expansion
  • Plantings grown near heat-reflective surfaces
  • Plants that are already indicating stress (yellowing foliage, wilting, leaf drop, dieback) (Dark & Hill, 75)

When during the course of a drought do we need to start watering our trees? A good visual rule-of-thumb is when the soil begins to separate from paved areas and around foundations due to lack of soil moisture. Shrinking soil place huge amounts of pressure on tree roots, which leads to rips, tears and even complete severing of roots. Drip irrigating is useful in applying water directly to the root zone while minimizing evaporation lose. Don't have a drip irrigation system? A dripping hose placed within the canopy line of a tree is my technique of choice and for those spots where the hose can't reach, a five gallon bucket with holes drilled in the bottom works just as well. Timing your irrigation depends somewhat on species, season and soil type but a general rule is to water slowly, deeply and allow the soil to dry out between watering.

Do not fertilize during drought conditions. Fertilizers promote growth in our plants, which is the opposite of what the plants are trying to accomplish as they slow down their processes in response to the drought event. Fertilizers are best applied when our plants are actively growing. Ideal fertilization for our cool season grasses and trees and shrubs occurs in the late-summer/early fall months with spring as the next best time of year. Most mature and naturally established woody plants rarely require fertilizer as they would not have grown in a spot lacking their nutrient needs.

After the Disaster

In a similar fashion to how our bodies begin to shut down organs when we become severely dehydrated, trees also shut down portions of their root systems during extreme drought. The effects of this root loss are often not immediately apparent in our trees, but over time it does become evident as the tree compensates the root loss with dieback in the canopy. The amount of time this takes often surprises homeowners. For instance, the drought of 2012 saw significant root loss of our trees, yet it isn't until the year 2015 that we anticipate canopy dieback to peak. This of course is a hard sell to homeowners whose trees are only now in 2014 dropping large limbs and some succumbing altogether.

After a severe drought, make sure to keep your eyes upward, examining your trees for dangerous rotting limbs. A certified arborist is your best tool to ensure the safety of you, your property and the health of your tree. You can find a list of certified arborists by going to the International Society of Arboriculture's website http://www.isa-arbor.com/home.aspx and search via zip code.

Preparing for Next Time

Adopting a proper watering schedule is key to the survival of your landscape plants during drought. This starts with creating zones in your irrigation system and limiting where certain plants grow. Trees replenish their water stores at night, making the ideal watering time from sundown to sunup. (Dark & Hill, 56) Yet, if water sits on vegetation all night this promotes disease pressure. This means that to water trees within the ideal window, drip irrigation is critical and turf is best left outside the dripline. Another reason for keeping lawn grasses out of the dripline of trees is that they are shallow-rooted with different irrigation requirements than our large trees.

Drought can happen any time of year. Giving landscape trees and shrubs a good soaking before the first hard freeze insulates the roots and will help if it is a dry winter. This is doubly important for evergreens which retain their foliage through the harsh winter months.

Install a rain gauge. Have you been receiving adequate rainfall? Or is the landscape deficient and needs supplemental watering? Rain gauges are an easy way to tell how many inches have fallen during a rain event.

Check your soil moisture. Yes this means actually getting your hands dirty. Most landscape plants prefer deep soakings with the opportunity to dry in between. Dig down a few inches and take a small amount of soil in your hand. If the soil is moist enough to form a ball, hold off on watering. You can also probe with a long screwdriver or go a step-up and use a digital soil moisture probe. Experience will breed familiarity with your soil, and over time you will easily gauge the water levels in your soil.

Mulch, mulch, mulch! Mulch works to insulate the soil so it can retain water. I prefer organic mulches (compost, wood chips, and shredded leaves) over inorganic mulches (rocks, rubber mulch). During hot, dry periods rock mulch radiates a lot of heat, further drying out plantings. Shredded rubber mulch on a hot day tends to smell of old tires, not a great aroma while enjoying your landscape.

Drought also sets the stage for wildfire. Wildfire is not as common in the Midwest as it is out West, but when dry conditions prevail, wildfire can pose a threat regardless of where you are. Firebreaks are the number one strategy to keeping your home safe if you live in a fire-prone area or have adjacent land use (i.e. upland timber, pasture, or prairie) that has the potential for wildfire.

Select species that are native and well-adapted to the conditions or your property. Some species are shallow-rooted and not as resilient to drought as those that develop extensive root systems. Below is a table of trees that are known to withstand drought conditions.

What aftereffects are you seeing in your landscape from the past two droughts? Are you beginning to see die-out in the canopy of your trees? Feel free to leave your questions and remarks in the comments box.

Next month: Floods

Trees Selected for Resistance to Drought (Hardy to zones favorable for Illinois)

Bald cypress

Taxodium disticum

4-10

Beech American

Fagus grandifolia

4-9

Birch, gray

Betula populifolia

3-8

Birch, river

Betula nigra

4-9

Blackgum

Nyssa sylvatica

4-9

Box elder

Acer negundo

3-8

Buckeye, Ohio

Asculus glabra

4-7

Cedar, eastern red

Juniperus virginiana

2-9

Cherry, black

Prunus serotina

4-8

Chokecherry

Prunus virginiana

2-10

Crabapple

Malus spp.

4-8

Elderberry, American

Sambucus canadensis

3-9

Elm, American

Ulmus americana

2-9

Elm, lacebark

Ulmus parvifolia

5-9

Elm, Siberian

Ulmus pumila

5-9

Fir, white

Abies concolor

4-7

Ginkgo

Ginkgo biloba

3-8

Hackberry, common

Celtis occidentalis

3-9

Hawthorn

Crataegus spp.

4-8

Hickory, shagbark

Carya ovata

5-8

Holly, American

Ilex opaca

5-9

Holly, deciduous

Ilex decidua

5-8

Hornbeam, American

Carpinus caroliniana

3-9

Inkberry

Ilex glabra

5-10

Kentucky coffee tree

Gymnocladus dioica

3-8

Linden, American

Tilia americana

3-8

Linden, littleleaf

Tilia cordata

3-7

Locust, black

Robinia pseudoacacia

4-8

Locust, honey

Gleditsia triacanthos

3-9

Magnolia, southern

Magnolia grandiflora

6-10

Maple, red

Acer rubrum

3-9

Oak, black

Quercus velutina

3-9

Oak, burr

Quercus macrocarpa

3-8

Oak, pin

Quercus palustris

4-8

Oak, Gambel

Quercus gambelii

4-7

Oak, red

Quercus rubra

3-8

Oak, Shumard

Quercus shumardii

5-9

Oak, white

Quercus alba

3-9

Pecan

Carya illinoinensis

6-9

Persimmon

Diospyros virginiana

4-9

Pine, Austrian

Pinus nigra

4-7

Redbud, eastern

Cercis canadensis

4-9

Serviceberry

Amelanchier canadensis

4-9

Spruce, Norway

Picea abies

3-7

Sweetgum

Liquidambar styraciflua

5-9

Sycamore

Platanus occidentalis

4-9

Viburnum

Viburnum spp.

2-9

Walnut, black

Juglans nigra

4-9

Table adapted from Weatherproofing Your Landscape by Sandra Dark and Dean Hill, University Press Florida

References

Dark, Sandra. Hill, Dean. (2011). Weatherproofing Your Landscape, A homeowner's guide to protecting and rescuing your plants. Gainesville, FL: University Press of Florida.



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