1. Water: too much or too little. Trees need water. Seems obvious, but there are a lot of people who believe that since no one waters forest trees on a regular basis, their urban cousins don’t need any help either. But that doesn’t take into consideration their very different growing conditions.

Forest trees conserve resources much more efficiently than their urban counterparts. For example, an organic layer of mulch holds moisture in the soil, natural wind breaks reduce evaporation, plus group shading and transpiration keep the overall forest temperatures cooler.

Urban trees often bake in the sun and may have to compete with a thick layer of sod over their roots systems absorbing a reduced level of available moisture. Buildings, streets, lights, and other urban elements radiate heat, further adding to the depletion of water.

How much is enough? Too much water is as harmful as too little.  Saturation of the soil can literally drown your trees by not allowing room for oxygen to penetrate into the soil pore space. A general rule of thumb is to perform deep-watering every 4-6 days during droughts for mature trees and every 2-3 days for smaller and newly planted trees.  Less frequent, but deeper watering will help train the tree to be drought resistant.  The best time to water is in the morning.

2. Poor soil conditions: All of the essential nutrients and elements necessary for good tree health, with the exception of sunlight, must be absorbed from the soil. When they’re not present, trees may become stressed. Lack of organic matter, soil compaction as well as grade changes during construction, all contribute to poor soil quality. A related problem is not enough soil for the potential size of the root system –in other words, a tree too large for the site.

A good way to protect root systems and rebuild the soil ecosystem is to add 2-4 inches of wood chip mulch over as much of the root zone as practical. Keep it off the trunk, where it can trap moisture and lead to trunk rot. Remember, root systems can often extend 2-3 times the canopy (or drip line.)

3. Structural defects. Anything that affects the structural integrity of a tree can have serious implications. Defects can include cavities and decay, splits, lightning strikes, "V" crotches, co-dominant leaders, cut roots or root decay, deadwood, etc.

Regular inspections can alert you to any obvious structural defects. Some defects, like "V-shaped" crotches and co-dominant leaders can be corrected if they are caught early enough. Lightning protection can help protect valuable specimen trees. Splits, cavities, cut roots or root decay must be taken on a case-by-case basis to determine the overall impact on the tree. In severe situations, the only safe option may be removal. When that is not the case, the damage should be monitored frequently. Deadwood should be removed before it is allowed to fall through the tree, possibly causing collateral damage to healthy branches, people or property. 

4. Storm damage. Storms can unleash incredible power and cause severe destruction to trees. Sometimes there is very little or nothing that can be done to prevent the damage.

But all too often the conditions within the tree are such that when the right storm comes along, damage is inevitable. These conditions include thick canopies that trap wind like a sail, deadwood that is just waiting to be blown out, and roots that have been damaged, leading to potential blow over.

Trees should be pruned periodically to allow wind to pass through the canopy to alleviate stress from wind sail. As mentioned earlier, deadwood should be properly removed to avoid collateral damage.  Pruning deadwood also allows the wound to close over correctly and reduces the likelihood of decay moving back into healthy wood.  Care should be taken to avoid damaging and/or compacting the root system. 

5. Improper planting. Many trees are doomed from the start by improper planting. Unfortunately, too often even landscape companies are not getting it right. Perhaps the most common mistake is either planting the tree way too high or too low. Other problems come from leaving burlap and wire baskets wrapped tightly around the root ball. Guying material is often overused and improperly attached to the tree.

Trees should be planted slightly above ground level. If the burlap can’t be completely removed or folded down into the planting hole because a loose root ball may fall apart, then vertical slits should be cut to allow emerging roots to grow out into the surrounding soil. Remove wire baskets as much as possible or cut with bolt cutters to avoid future root girdling.

Use staking and guying material only when necessary on trees with thick canopies that are subject to wind sail. Trees that are allowed to blow in the wind naturally develop much better trunk taper and have a stronger root system. In any event, make sure that the guying material used has a protective sheaf to keep it from damaging the bark. Don’t leave it on for any more than one year. 

6. Pest problems.  Research shows that most pest problems are secondary in nature. Pests and diseases tend to attack trees that are already under stress. Unfortunately, in the urban environment, many trees are under stress.

The best defense is a healthy tree. If your trees are getting the correct amount of water, nutrients, and oxygen, that will go a long way towards keeping them healthy. Proper pruning to get rid of dying, diseased, crowded, weak-attached, low-vigor branches and water sprouts in the crown will also help keep your tree healthy.

When more aggressive pest management is warranted, a certified arborist trained and licensed as a pest control technician can offer relief from the infestation. A word of caution -this is one area that requires specialized training. Most homeowners are better off leaving it to the professionals. To be effective, pest control applications must be done with the correct timing, with the right product, and in the right amount. Many chemicals sold over the counter can cause more problems to your trees than they cure when used improperly.