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Tree Care During Drought Conditions
Heat and drought conditions over the past few weeks are placing challenging conditions on most trees around Fayetteville. Also, many trees are already stressed from the record-low temperatures reached in February 2011. Weather-related stress makes the urban forest more susceptible to insect and disease infestations; however, residents and businesses can help nurture and protect trees by monitoring and watering them in times of drought.
New and young trees need the most water assistance during drought conditions because their root systems are not as expansive as large, mature trees. New and young trees should be watered weekly with a hose at medium pressure. Mature trees also need attention during drought conditions. Even when a summer rain shower occurs, the dry soil above the roots must first become saturated before much of the root system gains access to the water. Further, grass or lawn above the tree roots also soaks in part of the precipitation. Mature trees should be watered once or twice a month during drought conditions. Use either a shower-like attachment or just a plain hose to apply the water.
Water Calculation per Tree Size
How much water should be applied? Recommended watering time depends on the plant’s microclimate, drought tolerance, and other factors. In general, it is appropriate to apply 10 gallons of water per inch of trunk diameter per watering session. For this model, measure the trunk diameter at knee height. If it takes about 5 minutes to release 10 gallons of water from a hose at medium pressure, the following equation is a good guide: Trunk Diameter x 5 minutes = Total Watering Time. Therefore, if you have a young tree that measures 4” at the height of your knee, multiply 4” by 5 minutes to equal a total watering time of 20 minutes.
Symptoms of Drought Stressed Trees
How can you tell if your tree or shrub needs water? Conditions are currently dry enough in Northwest Arkansas that most trees would greatly benefit from supplemental water. Though drought symptom evidence may not show immediately, the following conditions are clear signs that a tree needs water:
1. Deciduous leaves droop or wilt.
2. Deciduous leaves curl. Leaves curl down to reduce airflow on the underside of the leaf and to decrease sun exposure on the top of the leaf.
3. Deciduous leaves turn yellow; veins or outside edges turn brown.
4. Evergreen needles turn yellow.
What are some tips on watering and saving water? Focus watering underneath the canopy of deciduous trees. Allow the hose to distribute water to different areas under the canopy. Conversely, evergreen trees should be watered up to five (5) feet beyond the dripline of the canopy. Allow the hose to apply water around the entire circumference of the evergreen tree. Focus on watering only the soil under or near the trees, and be sure that water is not being wasted on sidewalks, driveways, or on the leaves of trees. Although little rain has fallen here recently, times of dry weather are perfect opportunities to remember the value of this resource and consider collecting rainwater from future precipitation. Simple collection from the roof via gutters or piping and a barrel can reduce the amount of fresh water needed to pump from the freshwater hose.
Watering Techniques & Suggestions
The following are suggestions on efficient and effective tree watering:
• The best time to water is at night or early morning from 10 p.m. to 8 a.m. Trees relieve water deficits (refill) over the night-time hours. Watering at night allows effective use of applied water and less evaporative loss.
• Saturate the soil around the tree within the dripline (the outer edges of the tree’s branches) to disperse water down toward the roots.
• For evergreens, water 3’-5’ beyond the dripline on all sides of the tree.
• Deep watering to a depth of 12” inches below the soil surface is recommended. A few heavy (high volume) waterings are much better than many light, shallow waterings. A greater proportion of the applied water is utilized by the tree with heavy watering.
• The objective is to water slowly, dispersing the flow of water to get the water deep down to the tree’s roots.
• Avoid digging holes in the ground in an effort to water deeply. This dries out roots even more. A soil needle or deep-root feeder attached to a hose is acceptable to insert into the ground if your soil is not too hard and compacted.
• Overhead spraying of tree leaves is inefficient and can cause the tree to lose what water is held in the leaves. This should be avoided during drought conditions. Water should be released from the hose close to ground level.
• Trees in limited rooting areas such as in containers or pots, on major slopes, or confined by pavement, driveways, etc. need additional care to assure water is reaching the root system in adequate amounts.
• Do not fertilize during a drought.
• Treat pests or disease quickly. Drought stresses a tree or shrub and makes it vulnerable to pests and diseases. These factors further stress the tree and cause a downward decline in the plant.