Publication Date: Friday, September 09, 2005
Ivy busters
Ivy busters
(September 09, 2005) Ivy is not a friend of trees
by Forest Preston
For many of us the image of a well-tended lawn includes grass growing right up to the base of any trees that grow in it. Often we see ivy planted as an alternative groundcover below the trees.
Indeed, ivy seems to be a natural choice for planting below trees for it thrives in shade and is happy in a wide variety of soils. Although these under-story plantings may give an impression of a healthy and nicely manicured lawn, there is often a pending calamity hidden beneath them.
Grass and ivy and other groundcovers compete with the trees for water and nutrients. We tend to compensate for this with extra water and fertilizer. This may just compound the problem, especially for trees such as our native oaks that are adapted to dry soil in the summer.
The oak root fungus -- aka Armillaria root rot -- thrives in warm moist soil. I recall with sadness the signature pepper tree we had in a neighborhood in which I used to live. We killed it with kindness by watering it in the summer, not realizing that it was drought tolerant and very susceptible to Armillaria. By the time we understood what was happening it was too late.
So be sure to understand the soil and moisture requirements of your lawn trees and adapt your landscape care accordingly. The Canopy Web site (www.canopy.org/trees.html) has a very comprehensive listing of local trees with information on their growth habits, soil and watering needs, and overall suitability to our environment.
And consider more tree-friendly ground coverings. It's best to keep things such as ivy and lawn well away from the tree trunk -- as far away as the dripline if you can. Indeed, it is best to leave the soil alone under the tree canopy, at least for the three or four feet closest to the trunk.
Although I have seen very attractive alternative coverings of large pebbles, I have found that even they can hold the moisture. Bark and other organic mulching materials have the same problem and can also harbor fungus; if you feel you must use them, do be sure to keep them away from the root flare at the base of the trunk of your tree.
And in any case, be sure that you do not allow your lawn sprinklers to hit the trunk when you water; otherwise you invite another kind of fungus -- root crown fungus. Root crown fungus is one of the man parasitic fungi that live in our soils. With consistent, excessive moisture they become active and will begin to decay the tree. Without attention they will cause long-term decline and even death for your tree(s).
The best way to ensure that you don't introduce a fungus problem is to follow these easy steps:
** Remove competing plants like lawn and ivy. These plants can hide defects such as areas of existing decay and will trap moisture, making a perfect environment for fungus to develop. Worse yet, ivy creates a place for garbage to collect and thus makes a lovely breeding ground for rats.
** Remove built-up soil from around the root crown. By removing any built-up dirt you will expose the fungus to air (which it can't stand) and eliminate the moisture-holding material from the critical area.
** Water properly. Removing the lawn inside the dripline will eliminate competing plants and a source of retained excess moisture. When watering (assuming your tree is a non-native that requires summer watering), do not water in or allow water to collect around the root flare. Certainly do not allow sprinklers to spray on the trunk; water away from the trunk but still within the dripline.
And what about that ivy we say you should remove? Ivy is generally spread by seeds carried by birds. It's interesting stuff that can be a challenge to keep under control once established. It is undeterred by mulch.
Generally speaking, once ivy establishes itself under a tree it must be removed by hand with pruning. After pruning back the "ivy rug" you must attend to the "mother root," sometimes considered "the root of all evil." This root is big and impossible to dig out. But if it isn't destroyed, the ivy will grow back in a couple of years. So treat it with a herbicide like "Round-up." Arborist Cass Turnbull is of the opinion that the "Round-up" you use will pose less of a threat to the environment than the ivy itself does.
You'll probably get rid of 80 percent of the ivy the first time around using this technique. But you will still need to do additional weeding the second year and, if all goes well, even less the following years. In any case, though, don't expect total victory; this is tenacious stuff.
If you'd like to get some practice in the art of "ivy busting" join Canopy for one of its local outings; the next one is Sept. 17, 9 a.m. to noon at Mitchell Park in Palo Alto.
Author Forest Preston is a former Palo Alto resident who serves on the board of Canopy: Trees for Palo Alto, a non-profit advocate for Palo Alto's community trees. You can contact Canopy at (650) 964-6110 or info@canopy.org or send questions to Palo Alto Weekly, P.O. Box 1610, Palo Alto, CA 94302.
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