Re: selecting and growing azaleas
- James Thornton wrote:
> it's here and on line! the uga extentsion ofc publication"selecting
> and growing azaleas".this is a booklet by the uga in cooperation with
> the oconee chapter of the azalea society of america.
> take a look:
This is a fantastic document and represents a lot of very worthwhile effort.
I did find one problem. It states under "Site Selection" that:
"Materials commonly used to lower soil pH are wettable sulphur,
ferrous sulfate and aluminum sulfate."
While this is true, it is also true that repeated application of
aluminum sulfate is toxic to azaleas and hence it should not be
recommend. In fact, a note should be posted to warn against using
it. Unfortunately many people also are unaware of the problem.
Aluminum sulfate is great for hydrangeas but can kill many other
plants. Here are some references:
Mass. ARS Chapter by Joe B.Parks
"Never use aluminum sulfate to increase soil acidity as it is toxic
to many plants including rhododendrons. This is a most important
point! Under no circumstances should you use aluminum sulfate
(Al2SO4) around your rhododendrons. As was pointed out in a previous
article, soluble aluminum is toxic to rhododendrons. The chemical,
aluminum sulfate, is soluble in water thus the aluminum component is
immediately available - and toxic - to the plants. As the pH level of
the soil decreases, the aluminum component becomes increasingly
soluble - and thus increasingly toxic. Therefore, although aluminum
sulfate will certainly reduce the soil acidity, it can, and will,
quickly injure and may even kill your rhododendrons. Even though the
plants may tolerate small quantities of this material, why should any
quantity of a toxic material be added to the soil when other
perfectly safe materials such as sulfur are available?
I once saw an entire bed of rhododendrons (no, not mine) killed
within a week by a "proper" application of aluminum sulfate. Even
small amounts of aluminum sulfate can stunt rhododendron (and azalea)
roots and reduce their ability to absorb nutrients and water. True,
organic materials in the soil will buffer aluminum and reduce its
toxic effects, but the toxic effects occur immediately and the
buffering effect is slow. Too, how do you know there is sufficient
organic material available. Why take a chance with your valuable
plants, do not use aluminum sulfate regardless of what anyone tells
Hank Schannen of Rare Find Nursery
"Do not use aluminum sulfate to acidify the soil because aluminum can
be harmful to the plants over time."
H. Edward Reiley in Success with Rhododendrons and Azaleas:
"Plants in the genus Rhododendron are rather tolerant of aluminum,
but can be damaged by excess aluminum in the soil. Aluminum sulfate
should therefore be used sparingly, if at all. As soil pH drops
below 5.0, more aluminum ions become available in increasing numbers."
American Rhododendron Society [http://www.rhododendron.org/planting.htm%5d;
"Do not use aluminum sulfate to acidify the soil because aluminum is
harmful to the plants."
"Azaleas as Bonsai" by Jim Robinson (6/2/93) Rocky Mountain Bonsai
"Avoid aluminum sulfate or other aluminum compounds as aluminum is
too toxic to azaleas. "
Colorado Extension Service
"Aluminum sulfate will also lower pH, but it is not recommended as a
soil acidifying amendment because of the potential for aluminum
toxicity to plant roots."
Ohio State University [http://ohioline.osu.edu/hyg-fact/1000/1078.html%5d:
"DO NOT use aluminum sulfate to acidify the soil, as the aluminum
residue may be harmful to the plants."
University of Florida [http://hort.ifas.ufl.edu/gt/iron/iron.html%5d:
"Aluminum sulfate can be applied at the rate of one-fourth pound per
square yard of bed area. Do not apply aluminum sulfate more often
than one time in a 12-month period. Repeated use of aluminum sulfate
can lead to a toxic condition."
University of Minnesota
"Although aluminum sulfate is available in garden centers and also
lowers pH, it can be toxic to roots. There are better choices."
Organic Gardening Tips
"Because of the acid soil required, aluminum sulfate has probably
spelled the doom of more azaleas plants than any other single thing."
Cheers, Steve Henning in Reading, PA USA Zone 6
Visit my Rhododendron and Azalea web pages at:
Also visit the Rhododendron and Azalea Bookstore at:
- Bob Kelly wrote:
>That would the University of Georgia (UGA)-- the CooperativeActually the UGa Cooperative Extension Service is the part of the
>Extension Service. In other words, their Ag school.
Colleges of Agricultural & Environmental Sciences and Family &
Consumer Sciences that includes: county agents, home & garden
publications, supports the 4-H program, and answers questions about
agriculture, environment, youth, families, and consumer topics.
Their students are all the citizens of Georgia, not just the college
students. They do agriculture and consumer research and public
Land-Grant Universities were established under the Morrill Acts of
1862 and 1890. The mission of the land-grant universities was
subsequently expanded by the Smith-Lever Act of 1914 to include
cooperative extension - the sending of agents into rural areas to
help bring the results of agricultural research to the end users.
The Cooperative Extension Service, also known as the Extension
Service of the USDA, is a non-formal educational program implemented
in the United States designed to help people use research-based
knowledge to improve their lives. The service is provided by the
state's designated land-grant universities. In most states the
educational offerings are in the areas of agriculture and food, home
and family, the environment, community economic development, and
youth and 4-H.
Cheers, Steve Henning, Valley Forge Chapter, ARS; PA, USA Zone 6