Friday, October 19, 2007
Is it OK to pour salt water on the soil?
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.
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Q: We had a salt-water pool system this year for the first time. We are ready to drain our pool. Can we use this water to water trees and the lawn or is the salt concentration going to be harmful?
A: The salt concentration will likely harm plants. My recommendation is not to apply this water to the ground where desirable landscape plants grow roots and absorb water/nutrients. Ingredients in your pool water are already dissolved in solution, and thus available through "soil solution" to the plants. Let me explain my thoughts.
First, the type of soil you have determines the greatness of risk posed by pool water applied to trees and the lawn. Clay-type soil abundant in Roanoke will hold tightly to the liquids and particles dissolved in water more so than sandy soils generally found in beach areas, which have reduced retention ability and therefore allow faster drainage.
Look at the information that comes with your pool sanitizing salts for details and cautions on the risk involved. Look for the amount of sodium (abbreviation Na.) contained in the pool product. Sodium itself is toxic to living plants.
Also, what happens is the soil that receives the salt water from the pool will use its natural "rules" and eventually the roots living in that soil will die off. Accumulation of any particular mineral or salt present in the water poured onto the soil will be in a concentration greater than the concentration of that same mineral or salt that naturally occurs inside the roots in your soil. Think about the lesson on osmosis from your school science classes. Osmosis explains what happens in nature when the particles in adjacent liquids move through a membrane from the one with higher concentration to the one with lower concentration until both concentrations are equal. Thus, water will move out of the roots that contain no sanitizing salts to dilute the concentration of those same salts in the water poured from pool drainage onto that soil. This movement will suck the water from good roots attempting to reach that equalization. This is how "fertilizer burn" occurs when an excessive amount of nutrients are spilled or applied.
Q: Please explain care for an established shade tree, specifically for an old oak tree that has been in our front yard for over 60 years. I want answers to several questions. This tree has more big side branches on one side than on the other. I guess that is because the sparse side of our oak is surrounded by tree branches from our neighbor’s yard. A friend told me that those big side branches on our oak’s bountiful side should be cut off to balance the oak’s weight. Also, I was told that this should be done before snow and ice storms might occur. We live in west central Virginia. To help this oak cope with the drought, I saw somewhere that the tree should be fertilized. When? What else should I be doing for the oak?
A: Old age can be a problem for trees just as it can be for humans. Also, stress affects trees as it does people. Right now, the big stressor affecting many trees and shrubs is the prolonged drought we've experienced. Stress on trees is also caused by building houses, sidewalks and roads. Symptoms related to tree stress may not become apparent until many years after the physical activities occur. Thus, dealing with trees is not a predictable science.
It might be too late to completely cut off all or some of your oak’s big side branches. Even proper pruning can open up the area for decay funguses and/or various pathogens. Trees have a natural defense strategy to prevent entry of unwanted organisms. That strategy is to "wall-off" open areas to exclude or at least slow down those unwanted visitors. However, healthy trees can only wall-off so much of an area, so cutting healthy limbs larger than 3 inches in diameter is a bad idea. Instead, to lighten your oak’s weight on that heavy side, remove some of the side branches that have a diameter less than 3 inches that grow out from the big side limb itself. Wait until shortly after the oak’s leaves change color this fall but before the severe weather of winter to do the pruning. This will allow time for sugars produced by leaves on the cut branches to be sent down for storage in the trunk and roots this fall/early winter.
It's a good idea to fertilize this fall, shortly after the oak’s leaves change color, but just before the soil freezes. Even though scattering tree fertilizer under a tree’s canopy is good, I’d recommend "deep root feeding" to partially compensate for soil shrinking caused by the lack of rain on clay soils in this region. With this method, fertilizer containing the nutrient phosphorus is placed in a series of holes under a tree’s canopy. The holes work to aerate soil that has shrunk as a result of drought.
