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‘I’ve got a question about my tree…’ Part 2

Posted: June 26, 2014 10:32 a.m.
Updated: June 27, 2014 5:00 a.m.

Having received positive feedback to last month’s column, tree questions - part 1, I thought it appropriate to continue the series at least for another month, maybe even for the rest of the summer, as there are lots of questions about trees!

How much should I water my tree?

Now that summer is officially here and temperatures are high, it’s important to keep our plants and trees supplied with adequate amounts of water to keep them healthy. How much water is adequate is the tricky part. Most folks think we get more water than we actually do during rain storms. Here at the Public Works lot, we’ve mounted a rain gauge to monitor the definite amount received; so if you happen to see me watering our new trees shortly after a rain, it’s because we didn’t receive enough water to sustain the trees for the week ahead.

Contrary to what some believe of the saying “If you water deeply, the roots will grow deeper,” this is not the case. In fact it’s just the opposite! Tree roots need four things to survive: water, oxygen, nutrients and space. Each component is essential. Deficiencies of any one aspect may negatively affect the long term health and growth of a tree. If the landscape is watered in large quantities with the intent of growing ‘deep’ roots, the water particles will end up occupying all of the available underground pore spaces and not leave any room for oxygen molecules. Since oxygen levels decrease in volume the deeper into the soil you go, so does the ability of the tree roots to grow deep. This is why most tree roots grow in the upper 12 inches of soil: no matter how much you water because oxygen cannot actively permeate the soil unless aeration methods are used.

In fact, too much watering over a long period of time can actually hurt a tree. Wet soils have very little oxygen. This may lead to root suffocation, drowning and death as a result. This in turn, reduces the trees’ ability to provide water and nutrients to the tree which begins a cycle of declining health. It’s best to allow the soil to dry out to the point of just being moist to the touch but not bone dry. This takes some initial monitoring particularly if an in-ground irrigation system is being used.  

When watering our newly planted city trees, the general rule-of-thumb I use is 5 gallons of water for every 1 inch of trunk diameter (measured 6 inches above the ground). This varies from tree species to tree species. Evergreen trees, such as holly and cedar, tend to ‘drink’ more water than an oak or maple tree. Trees that were grown in a nursery with clay soil will need a less water than those grown in sandy soil. The time of year and size of the tree also dictate how much water is needed each week. Trees transpire water from their leaves to stay cool (our equivalent of sweating). This requires more water during the summer than the winter. Larger trees need more water than smaller trees because they have more leaves and woody biomass to maintain.

The city is committed to watering our new trees for the first two growing seasons, from March through November. This is important for their survival and establishment in the landscape. Most of these trees receive a minimum of 10 gallons of water per week, some get up to 25 gallons per week. If you happen to have a young or newly planted tree, be sure to provide water directly to the root ball each week. Using a 5 gallon bucket is an easy way to keep track of the watering quantity, which can be adjusted depending on how quickly the root ball dries out or stays moist.

If young and newly planted trees need so much water, how do large trees survive the hot dry summer? Large, established trees have developed an extensive root system (provided there is enough space for them to do so) and have acclimated to the normal growing conditions here in town. Supplemental water from home irrigation systems certainly help to keep these giants hydrated. Large, healthy trees also have a tremendous amount of stored water reserves throughout the root system, trunk and branches that it taps into during dry spells. However, during extreme and consecutive heat (98 to 100 degrees) and prolonged drought conditions, I’ve witnessed large old trees practically die overnight. This is due to the lack of available water in the soil and the use of all the internal water reserves, which stops all physiological processes and the tree dies. The bottom line is, not enough water can be just as detrimental as too much water.

Lightning hit my tree. Will it die?

As mentioned in my column last month, the answer to many tree questions is “It depends.” This is one of those questions. Lightning kills trees by vaporizing the water reserves stored inside, in effect dehydrating it from within. Since we can’t measure or know the strength of an individual lightning bolt, we have no way of determining the extent of internal damage. However, it’s been my experience that hardwood trees normally withstand and survive lightning strikes better than pines. When lightning strikes a pine tree, like it did recently in Hampton Park, the tree has about a 50-50 chance of survival if it’s healthy. Many times, if the lightning doesn’t kill the pine, then boring beetles will because they sense the chemicals emitted by the tree as a result of the wound. In general, it takes about three to four months to say for sure whether or not the pine will make it.

In the meantime, a remedy to help the injured tree (pine or hardwood) is to provide supplemental water and install mulch under the canopy (if possible) to retain soil moisture. In regards to the physical scar or streak a lightning bolt may leave, it’s best to leave it be and let the tree close the wound over time. If chunks of wood have been blown off within an area that can be reached, it’s best to cut away the loose wood. No paints, tars or chemicals are needed to apply to the area. The tree will develop new wood to grow over the area over time. If you can’t stand the sight of the bare wood, spray regular old paint for aesthetics.  

In the long-run, the best thing we can do for our trees is to keep them healthy by providing some basic necessities: supplemental water when we have a dry spell, room to grow, aerated soil and mulch. It’s really as simple as that! If you have any questions regarding a tree problem that has not been addressed or would like an on-site consultation, feel free to contact me at the Camden Public Works Department.

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