Tree WateringWater

Yes, you should water your trees whether or not there is a drought. The infrequent rainstorms locally do little to moisten the soil deep enough for trees to benefit year-round. Many of the planted trees in Santa Barbara are from other parts of the world where rainfall totals may be higher. Even native trees need supplemental water now and then. If we water trees regularly and appropriately we can prevent issues that can occur during an extended drought.

Common symptoms include: wilting of the leaves and small branches, smaller or partially dead leaves, thin canopy, out of season changes, heavy flowering or fruiting, dieback and branch death. Keep in mind that these symptoms can be caused by other things; contact an arborist if you are concerned about the health of your trees.

Trees need slow deep watering so that the water gets down a minimum of 12 – 18 inches below the surface. Utilize slow drip methods to apply water such as a soaker hose, drip irrigation bucket or use a deep root watering probe (pictured to the right) that delivers water below the soil surface.

Watering your tree with lawn sprinklers will not provide enough water for the tree. Sprinkler water does not soak deep enough into the soil to reach tree roots, and these ground covering plants use up the water before the tree can get to it.

The roots that absorb water and nutrients are only close to the trunk for about the first 5 years of a tree’s life. After that, these feeder roots are farther out. The optimal place to water older trees is near the drip line, which is the outside edge of the tree canopy where rain would drip down from the leaves. Ideally, you want to water the area half way between the trunk and the drip line, and up to the same distance beyond the drip line. Refer to the diagram below. Mature trees do not do well when the trunk gets wet.

Sometimes these areas are covered by our homes, driveways, sidewalks and other impervious areas, in these cases do the best you can. Watering in a lesser optimal location is better than no water.

Apply a 4 - 6 inch layer of mulch in the optimal watering area and remove weeds and other competing ground covers. Don’t apply water to other areas. These steps will reduce evaporation and water loss. Utilize slow drip methods to apply water such as inline drip or a soaker hose, or use a probe that delivers water below the soil surface.

You can tell if your tree is getting enough water by checking the soil moisture. Since tree roots are deeper than roots of other plants, dig down 6 – 8 inches below the surface before watering your tree. Squeeze some of that soil in the palm of your hand. If the soil clumps there is sufficient soil moisture. If it falls apart there is too little water, if it smears like a paste it is too wet.

During the drought we all need to practice water efficiency and conservation, especially in our landscapes. In general, you should water any rare plant that would be hard to replace. With a limited amount of water, it is beneficial to prioritize trees over shrubs, lawns, and other groundcovers. Trees take many years to mature, and once they do they provide many community and environmental benefits such as shade, improved air quality, and even higher property values. If we let our trees die from lack of water, we have lost an investment of many years. Additionally, it will take many years to get back the benefits we had before the tree died.

If piled too high, mulch can become a fire hazard. Keeping a mulch layer 4 – 6 inches deep provides the benefits that trees need without being piled too high to create a fire hazard. Another solution is to leave the fallen leaves and twigs that come from the tree in place, don’t rake them up. This natural mulch releases nutrients back into the soil that the tree can reuse.

When there isn’t enough water in the soil for a tree to take up, the tree will close the pores in its leaves that respire oxygen and residual water (this process is called transpiration) until temperatures are cooler or moisture is available. If the moisture level remains too low for extended periods of time, the tree will use up stored water and the leaves will begin to wilt. If dry conditions continue the tree may drop leaves early or die back. Sometimes trees produce excessive fruit in an effort to help the species survive. If a tree is deciduous it may go deciduous early or develop leaves later than normal.

If you notice these conditions occurring in your tree, check the soil moisture to see if there is enough to support water uptake. Refer to the question above, "How can I tell if my tree is getting enough water?" for information on checking soil moisture.

Maybe not. There are many reasons trees drop leaves. This is a defense mechanism for trees to survive periods of stress, either natural or induced. During the drought deciduous trees have dropped their leaves early and have leafed out late. Evergreens can also drop their leaves and not be dead. Sometimes an insect or disease causes leaf drop or leaf death. Before you have a tree removed have an arborist check to see if it is truly dead or just dormant.

There can be many causes of this but during the drought, stressed trees might produce more fruit or more crops of fruit each year as a mechanism to provide for survival of the species. Check the soil moisture to see if there is enough to support water uptake. Refer to the question above, "How can I tell if my tree is getting enough water?" for information on checking soil moisture.

In most cases no. It is pretty rare that trees need fertilizer. It is almost always bad for trees to get supplemental nitrogen from fertilizing. Nitrogen causes trees (and other plants) to use energy to develop green leaves. If a tree is stressed, forcing a tree to use these energies saps its reserves that might be needed to fend off attack from insects or disease. Rather than applying fertilizer, leave the fallen twigs and leaves underneath the tree; as these decompose they provide nutrients back to the tree.