GardenBanter.co.uk - View Single Post - Sulphur to lower pH for iron chlorosis in pin oak trees

David E. Ross · 19-10-2007, 04:23 AM posted to rec.gardens

On 10/18/2007 3:17 PM, wrote:
I have been using Medicap Fe trunk implants very successfully to fight
iron chlorosis in my many pin oak trees for 15 years. Soil samples
show my pH to be 7.3 minimum and 7.6 near our long concrete cement
driveway. The soil report recommendation is to add 32 pounds of
sulphur (sulfur) to a depth of 12 inches per 1000 square feet (or 8
pounds to a 3 inch depth). Several internet sources recommend putting
the sulphur in approx. 12 inch deep holes in a 2 foot by 2 foot grid
around the tree. They also suggest a 1 to 1 ratio of sulphur and iron
sulfate (ferrous sulphate/copperas) to add iron in addition to
lowering the pH.
Question 1: Will the localized high sulphur concentrations do harm to
the trees?
Question 2: What is the highest sulphur application rate for grass
(lawn) (bluegrass and fescue) without damaging it?

To acidify your soil, the sulfur must be converted into sulfuric acid by
soil bacteria. This happens slowly. For best results, make several
light applications repeatedly instead of applying the entire amount all
at once. This will help prevent killing the beneficial soil fungi since
sulfur is a natural fungicide. It helps if there is a good leaf mulch
that has started to decompose into leaf mold. (Oaks really need this in
their root zone.) Then the sulfuric acid will be formed on the soil
surface, and you won't have to dig. (Digging in the root zone of an oak
can kill the tree.)

You should also add some gypsum (calcium sulfate). A significant amount
can be added without the damage that might be caused by a significant
amount of elemental sulfur.

In the end, you will find that it takes more work and time to acidify an
alkaline soil than it takes to neutralize an acidic soil.

By the way, in my area, native oaks thrive in the native soil, which
tends to be alkaline. However, pin oaks (Quercus palustris) are native
to the eastern U.S. where many soils are indeed acidic, not California.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening pages at http://www.rossde.com/garden/