During long periods of dry soil, temporary wilting grades into permanent wilting. Permanently wilted trees do not recover at night. Permanently wilted trees recover only when additional water is added to the soil. Prolonged permanent wilting kills trees.
Trees may decline slowly as issues wear down their resistance to damaging insects and diseases. Less growth, off-color or smaller than normal foliage, early leaf drop, cracked bark and dying branches are all indications that a tree may be under stress.
Drought or dry soil conditions result in root damage and death. In addition to direct root damage, weakened trees are subject to many secondary problems including root rots, cankers, wood rots, and increased sensitivity to pesticides and de-icing salts.
Trees in a drought should still be hand watered about twice a month at a minimum. During the hottest parts of the summer, and especially in hotter and dryer areas of California, trees need watering twice a week.
Proper tree care during drought includes watering, mulching and pest management. Applying organic mulch such as wood chips to a depth of 2 inches will help the soil retain moisture. But if the soil does not have any moisture, mulch will have little effect as there is no water to retain.
When you spot trees that have curled or wilted leaves that may be turning brown at the edges or tips, you might have some underwatered plants. Sparse canopies that are off-color and have undersized leaves, yellowing leaves, or scorched leaves are also major tell-tale signs of dehydrated trees.
Signs of Heat Stress in Trees
Wilting leaves are typically the first thing you'll notice. As the tree becomes more stressed, stems and branches can start to droop. Irregular yellowing of interior leaves or needles. Failure to produce healthy-looking new growth, making the tree canopy look sparse.
There are a few things you should avoid doing to your trees—newly planted or mature—during a drought. Don't fertilize trees. Fertilizing pulls water from the roots and forces the tree to expend energy processing the fertilizer which is an additional stressor.
Deeply and slowly water mature trees 1 – 2 times per month with a simple soaker hose or drip system toward the edge of the tree canopy – NOT at the base of the tree. Water comes out of your full volume hose at about 10 gallons per minute while the most common drip emitter gives 1 gallon per hour per emitter.
However, younger trees are able to recover quicker from drought conditions, usually within one year. Mature trees typically require several years to bounce back, if they ever do. If your tree doesn't look better after a few solid days of watering, you might want to call an arborist near you for help.
Visually divide the area around your tree into 4 sections. Place the hose about 2-3 feet from the trunk in section one and let the water soak into the ground for about two hours, move the hose to another section until you have fully watered all four quadrants over the period of a day.
If you are wondering how to rehydrate a tree, water it around the drip line, offering sufficient water to get down to the feeder roots, but also to the larger roots beneath.
Get a pinch of dirt (be sure that it is dirt and not mulch) and roll it around between your fingers. If it sticks together, there is enough moisture. If it is dry and crumbly, it is time to water. If it is muddy and hard to grasp, the area is receiving too much water.
After the heatwave has passed, look closely at your trees to see if they are recovering. If you don't notice any signs of improvement, contact a Certified Arborist for a consultation. Keep in mind that heat stress can have lasting effects on a tree – some symptoms may not appear until years later.
In general, a heat-stressed plant will have leaves that are yellowed or exhibiting some brown spotting. This is usually accompanied by wilting. They may look burned in some places, particularly if they are also receiving too much light.
Signs of Overwatering and Underwatering Trees
The tree's leaves are the first places to look for stress, but you may notice negative changes in the bark and branches, too. Here are some signs you're under-watering your tree to look out for: Wilted, curled, or dead leaves.
Look for cavities and cracks in the trunk, branches and bark. If the bark has large bald spots, large cracks or sections of it are falling off the tree, this is a problem. Large cracks or hollows in the trunk or main branches indicate they are not strong and healthy.
Dry rot begins as a microscopic spore which, in high enough concentrations, can resemble a fine orange dust. If the spores are subjected to sufficient moisture, they will germinate and begin to grow fine white strands known as hyphae. As the hyphae grow they will eventually form a large mass known as mycelium.
Overall, supplemental watering, especially when summer conditions are hot and dry, and the use of wood chip mulch, will go a long way to helping trees remain healthy and better withstand dry conditions and common pests. Many trees have survived extreme droughts in the past.
The first evidence of drought is usually seen in records of rainfall. Within a short period of time, the amount of moisture in soils can begin to decrease. The effects of a drought on flow in streams and reservoirs may not be noticed for several weeks or months.
Watering should take place every day for approximately 15-20 minutes, depending on the pressure in your system. Of course, if it rains that day, no watering is necessary. It is best to water in the evening or early morning when the sun isn't up.