I planted a river birch, Betula nigra , May 2000. Each year starting early summer the leaves start turning yellow (some developed purple spots), die & fall off. New leaves will regrow, but they too die early. There is no sign of insects. I read that river birch like slightly acidic soil so I started feeding the tree last summer with a water soluble soil acidifier (33-11-11). It doesn't seem to have helped. I dissolve the plant food in a watering can and simply poured it on the ground around the tree. Is this an effective method of acidifying the soil? If not, how should I be doing it? Do you have any idea what might be the problem with the tree? It is planted in an open area and does not lack water.
The yellowing you see is likely caused because one or more soil nutrients are in short supply. Commonly, a lack of iron, or occasionally, manganese, can cause this chlorotic condition. These elements may be in short supply, but the ability of your birch to pull these from the soil is made worse higher pH levels, such as 7.0 or higher. Deficiencies of these elements are commonly due to a high pH rather than simply a lack of these nutrients in the soil. Betula nigra is known for being slightly intolerant of alkaline soils, so the yellow leaves tell us your soil is probably alkaline. What's missing, though, is a clear sense of your exact soil chemistry. I assume your soil is clay, because iron chlorosis is more common in a heavy soil.
As you read in the (above) publication, you'll note there are two ways of treating the chlorosis that are recommended to the non-professional. Spraying the leaves with a mixture of a commercial product such as Acid-gro, or Mir-acid, according to the package directions, should show some fairly quick response. To bring about long-term results, though, you'll have to follow the directions for incorporating either elemental sulfur or iron sulfate (one or the other, not both) into the soil. The important thing to do right now is to read about how to get your soil tested. The important thing to do right now is to read about how to get your soil tested, (There is a small fee for this service.) Hewre's the ink to the Soil Testing Lab:
I also wonder exactly how much of the 33-11-11 fertilizer you actually used up until now. How many pounds were in the package, and what percent of the original is still unused? Too much of this may have built up "salts" in the soil around the tree's roots. Excess soil salts can only complicate the stress your tree is experiencing, so discontinue the use of this fertilizer. If you used a pound or two, it's likely no harm was done.
