From: Bob.Batson@mtask.omahug.org (Bob Batson)
Newsgroups: rec.gardens
Subject: Bark in Growing Mixes
Date: 13 Oct 92 17:51:31 CST
Reply-To: bob.batson@mtask.omahug.org
Organization: Multitasking Systems, Kansas City
Followup-To: rec.gardens

               Potential Toxicity of Bark in Growing Mixes

  If you grow potted plants using growing mixes which contain bark, you
need to be on the lookout for phytotoxicity symptoms. That's according to
Bob Ludekens who runs a commercial nursery in California. And he should
know---he has spent 22 years investigating plant damage due to toxic
materials in growing mixes. He says that tannic acids in some types of
tree bark used in growing mixes can damage plants HAVING RECENTLY PRUNED
ROOTS (for example, trees transferred from nursery rows into containers).
Oak (Quercus), cedar (Cedrus), false cypress (Chamaecyparis), arborvitae
(Thuja), fir (Abies), slash pine (Pinus Elliotii), and redwood (Sequoia)
barks have high concentrations of tannic acids; they should be stockpiled
in an exposed location to allow leaching of the water-soluble toxins
before being added to growing mixes. An alternative is composting the
bark.
  Ludekens reports that the following plants are particularly susceptible
to damage due to tannic acids in bark; apple and crabapple (typically not
fatal; sensitivity depends on cultivar), cherry, fig, peach and nectarine,
pear (especially `Aristocrat', `Bartlett' and Asian cultivars; symptoms
are like fireblight, but black areas move out toward branch tips than in),
almond, pecan, walnut, apricot (especially `Peggy Clarke', which can serve
as an "indicator plant" for low tannin concentrations), `Fan-Tex' and
`Raymond' ash, birch, variegated boxelder, desert willow, golden-rain
tree, hackberry, hawthorn, redbud, smoke tree, California sycamore, tulip
tree, Japanese zelkova, almond, lilac, wisteria, artichoke, horseradish,
rhubarb, several bramble species, grape, Monterey pine, several bedding
plants, and some rose cultivars.
  Remember, tannic acids in growing mixes apparently DON'T harm plants
with intact root systems, so there should never be phytotoxicity problems
when transplanting from a small pot to a large one. Just be sure that you
don't break off or cut some roots (especially, we presume, large ones).
  For additional information, contact Bob Ludekens, L.E. Cooke Co., 26333
Road 140, Visalia, CA 93277 [U.S. of America]; phone 209-732-9146.
  Reference: Sami Harman Thomas, "Grower Says Tannic Acids Can Be a
Problem," _NURSERY MANAGER_ 8(8), August 1992, 68-70. (Branch-Smith
Publishing, 120 St. Louis Ave., Ft. Worth, TX 76104.)
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Reprinted with permission from the September 1992 _HortIdeas_. Copyright
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Bob Batson
bob.batson@mtask.omahug.org

Newsgroups: rec.gardens