|A Long Spell of Dry Weather|
That is Merriam-Webster’s simple definition of drought. That’s all they say. Short and to the point. Allow me to tell a story. In 1968, for reasons still curious to me, I joined the Marine Corps, not the best timing to say the least, but my decision. While in boot camp I learned many useful skills, some thankfully forgotten and others I use to this day.
During survival training we were taken through rigorous conditions that included a 24-hour period with no water to drink. During that time, we were taken through our daily exercises, meals, close order drill and physical training. By noon there was only one thing on our minds. We could no longer perform daily functions due to the stress we were under. Any one of us would have begged, borrowed or stolen to get our hands on earth’s most valued possession. It brought our platoon together for only one objective, that of survival. I will never forget the experience and pray I never experience it again. As I witnessed first hand, humans can only last for a few days without water, but how do trees and shrubs do it? How can they go for years with little to no water?
It is a biological fact that the Plant Kingdom is more successful than the Animal Kingdom. In many ways woody plants are more resilient than humans. Because of their biological make up they can withstand periods of environmental stress, but have their limitations. Older woody plants are better equipped to survive these times of stress, than younger plants. What can we do to help our trees and landscape endure the current lack of water? Many areas may experience water restrictions due to current conditions. This makes the planting of new trees and shrubs even more difficult. Fall of 2000 and 2001 gave us serious drought conditions and were responsible for very little root growth in woody plants. This predisposed many species to a stressful growing season to follow. So what happens next and what can we do to help???
The watering of large shade trees is difficult. However, the watering of young trees is paramount. How do we efficiently water young trees? I planted three Burning bush this summer just to see how they would react by being planted at a more difficult time than usually recommended. I religiously watered these three plants twice per week by soaking them slowly. I made sure they absorbed water as I soaked them and did not allow any water to “run off”. By being consistent with my watering they are alive today. Water your young plants slowly but thoroughly. Allow water to soak in and then water again and again until the root zone is saturated. This is all done at the same watering period, waiting a few minutes between soakings. Water heavily and infrequently rather than everyday, twice per week when plants are young. You and I should drink 8-10, 8 ounce glasses of water per day for optimum hydration. Young plants, on the other hand, should be given water all at once and then be allowed to dry before the next dousing. It is possible to love our plants to death. Few varieties of plants can live with “wet feet”, so even during drought check the soil around plants to be sure they are ready to accept your water.
Watering is crucial, but how can we keep that water within our plant’s root zone for longer periods of time? Dr. Rex Bastian, Vice President of Field Education at The Care of Trees uses three words that spew from his mouth like water from a hose, MULCH, MULCH, MULCH! His point; if you can grow your trees in mulch rather than grass, your watering program will be more successful. 1-3 inches of mulch, out to the tree’s dripline will hold moisture in the soil, loosen compaction and introduce earthworms and other organisms so important to soil density, texture and makeup. Remember, never place mulch against any woody parts of your plant’s trunk. Grass is of no organic benefit to trees and will covet valuable water and nutrients. Mulching is quite simply the simulation of the natural forest environment. Building that natural humus layer back under our plants is the most positive step we can afford our urban trees. Here’s something positive to think about next time you design your tree plantings. Plant trees as a group rather than as a single tree surrounded by a typical donut of mulch. Can you picture it? Trees rarely grow as individuals, but almost always appear as a group, taking every opportunity to connect with each other in an effort to become more successful. Trees in groups do marvelous things such as root grafting. That’s right! Trees of like and unlike species actually graft their roots and share elements within the soil. This is an incredibly successful tactic used by trees over millions of years. Do you think we could change the way we plant and grow trees?
Watering, mulching and correct pruning will help keep our trees on the straight and narrow. Just as preventative medicine affords us with fewer trips to the doctor, we can give our plants the same comfort by understanding how they operate as organisms. Trees that are healthy can withstand the ravages of stress, such as drought, better than those that have become weak due to poor health care programs or no program at all. Organisms such as borers and mites will find trees weakened by environmental conditions. Examples we have seen in our area have been, shot hole borer on white pine, bronze birch borer on white birch, mites on evergreens and various other pests at levels higher than in years with significant rainfall. We may find it necessary to treat pests that reach intolerable levels during these difficult times. Your arborist can help you make decisions about which pests need treatment and those we need not worry about. Remember, pests have their own natural predators. It is important that your arborist recognizes the different situations that require treatment and those that should be left to their own defenses. It all comes down to education, doesn’t it?
Fertilizing trees and shrubs can be a beneficial part of your “drought” maintenance program. Do all trees need to be fertilized? Probably not, however those that cannot be mulched or are too large to water may benefit from a soil-amending program. Fertilizer installed through pressurized water injected directly into the root zone, early or late in the year, may be beneficial to your woody plants. This type of fertilizing not only supplies water to the soil but also gives the tree quick and slow release nitrogen that may be deficient in your soil. Again, walk with your arborist as fall or spring approaches so they may answer your questions about such programs.
Here is a list of trees that I believe to be more to drought-tolerant than others. Many of these are being used presently in difficult urban situations: Bald cypress, hackberry- great wildlife advantages, chestnut oak- available at some nurseries, willow oak, sweet gum, black gum, European hornbeam, gingko, white oak as well as most members of this genera, to name a few. Look over this list. Where do many of these species grow? In what ecosystems do many of these trees thrive? You guessed it. Many of them are riparian, or water tolerant. Trees that naturally thrive in wet situations seem to be able to handle drought. Very interesting!
Let’s summarize: Water your young trees slowly, thoroughly and infrequently. Be sure the water is penetrating the entire root zone. Mulch those trees for water retention and organic breakdown around tree roots. Again, never put mulch or soil against plant stems or tree trunks. Keep your trees free of deadwood, this will give insects and diseases less availability and harborage during times of drought stress. Fertilize those trees that cannot be mulched or watered. The combination of these programs is the key. An educated, integrated program that assists our trees in becoming what they would most naturally is the signature of good plant health care. Talk with your arborist and ask questions. We’re here to help and look forward to our next visit with you. Oh, by the way, be careful what you sign. The Marine Corps is not for everyone! Good health to you and your plants, Peter!
Copyright 2008 by Peter Deahl. All rights reserved.
The Pruning School 16 Berkeley Court Sterling, Virginia 20165