I find it very interesting that my clients are so ready to pay me to do what ever it takes to make their trees healthy. More often than not, the advice that I give people does not involve spending much money.

What a tree needs to be healthy is very basic. It is the same thing we all need, a healthy environment to live. For us that means enough clean water to drink, plenty of clean air to breath and enough of the right kinds of food. That’s pretty basic but I’m using that analogy to help you understand what a tree needs to be healthy.

Water

Myth - A large tree has roots that get down to the water table and doesn’t need any extra water". I have heard this statement and it is not true. First, it is important to understand that the majority of a large tree’s root system (that absorbs water), is within the top 18" of the surface. Some types of trees need more water than others so understand the needs of your particular variety. Irrigation needs to be monitored and you need to dig down to see if the water is penetrating to the root system. All too often I see a drip system that is fine for the small plants but when I dig down a few inches, I find it bone dry. Know where to water. A root system on a large tree spreads clear out to the edges of the canopy and beyond. The most important roots for absorbing water are the root tips, out at the ends. Watering the trunk area roots do not help much in getting water to the tree, you need to water out and away from the trunk. Over watering can be a problem if the soil does not percolate through and the roots end up drowning in water. How do you know if the soil is percolating through? Easy, dig a hole, fill it with water and wait for it to seep through. If the water sits there over night, you may have a hard under surface that is going to make things tough on your tree. Dealing with sub-surface compaction is another topic but a very important one.

Air

Oxygen in the soil is as important as water. Soil that becomes compacted from either construction or people pressure or roads or houses, is soil that is very difficult for roots to develop in. If the damage occurs while the tree is there, then you have a long downhill decline in health. Air space in the soil is also important for water retention. So the point of this is also basic. Don’t mess up the consistency of the soil. A healthy tree takes in carbon dioxide through its leaf mass and gives us back oxygen for us to breath. Fair trade off if you ask me. We just need to realize and appreciate how important it is to allow a tree the space it needs and how to protect the roots and soil structure. Construction damage from soil compaction is a major problem with the decline and death of a large part of the old trees in our cities.

Food

Food for a tree is really about sunlight and photosynthesis converting light into sugars. A tree needs enough leaf mass to help it to feed it’s self. A healthy full tree does a pretty good job of providing for it’s self. A big problem comes when we over trim the trees or cut them in a manor that causes a leaf reduction greater than what the tree needs to sustain it’s self. I am not talking about fertilizer as food for the tree; I am talking about gathering enough sunlight through the leaves. A healthy tree is a full tree. Taking away too many branches will cause a slow reversal in tree development. Over trimming a tree can cause a long term tree decline. Without getting into the whole science of tree physiology, all I am trying to get across is that a full, balanced canopy is what a tree needs. Fertilizers are sometimes needed to help a bad situation. Another thing that people don’t really understand is how leaf drop aids the soil. All too often the gardeners blow away all the leaves (natural mulch), when they really should be allowed to stay and improve the soil. I know this is not always possible, but if you can think about what a tree needs, rather than what you want, you might find some compromise that works both ways.