Question
QUESTION: I planted a weeping oak about 3 years ago.  It grew about 6 feet taller (its probably about 30 feet tall now) and each summer the leaves are increasingly yellow.  The veins are green.  I am concerned that the garden center that planted the tree may have left the tree in a wire basket.  I've been told that should not matter.  My other concern is maybe it is not getting the nutrients it needs.  I appreciate any help and guidance you can provide.

ANSWER: Trees that exhibit yellow leaves with prominent green veins are often suffering from a micronutrient deficiency called iron chlorosis. Symptoms may range from a mild yellowing of the leaf tissue between the veins to severe yellowing. This can lead to the death of leaves, dieback of branches, lack of vigor, and possibly death of the entire plant.

Iron chlorosis is often a problem of pin oaks, though other tree and shrub species can be affected. Chlorosis is typically associated with one of three site conditions--a soil with a pH above 7 (an alkaline soil), a heavy soil containing a high percentage of clay, or a site where there has been extensive soil fill or removal, compaction, or construction injury that has damaged the root system. Older, established oaks are especially subject to the latter type of injury.

Use soil applications to treat individual trees and shrubs, or small areas in a landscape, in the fall or early spring. A mixture of equal parts iron (ferrous) sulfate  and elemental sulfur can produce lasting results and is relatively inexpensive. Select an inorganic iron source with a high concentration of iron and one that is derived from iron or ferrous sulfate. Read labels to determine iron concentrations and forms in different products.

It is not practical or desirable to blanket an entire landscape with the elemental sulfur-ferrous sulfate combination. Instead, treat small areas by making holes 1 to 2 inches in diameter and 12 to 18 inches deep. Space the holes 18 to 24 inches apart around the area within the drip line (outer edge of crown) of affected trees and shrubs. Fill each hole with the iron sulfate-elemental sulfur mixture to within 4 inches of the soil surface. For a small tree make about six holes and use a total of about 2 Pounds of combined elemental sulfur and iron sulfate. Make holes with an auger or soil probe that removes soil to reduce compaction. Avoid damaging large, woody roots when making holes.

Some commonly available sources of iron and sulfur.

 Source  Trade name Content (% iron)   
 Inorganic iron:      
 Ferrous sulfate Iron sulfate  20.5   
 Ferrous sulfate Ionate 10.0   
 Ferrous sulfate  Bandini 7 iron 7.0   
 Ferrous sulfate Ironite  4.5   
 Acidified mining residue Iron-Sul  20.0   
      
 Iron Chelates:      
 FeEDTA Sequestrene 12.0   
 FeEDTA  Hampene Iron 9.0   
 FeDTPA  Sequestrene 330 10.0   
 FeEDDHA  Millers Ferriplus 6.0   
 FeEDDHA Sequestrene 138 6.0   
 FeHEDTA Che-Gro Iron  5.0   
 FeHEDTA Versonol Ag Fe  5.0   
      
 Sulfur:  %sulfur   
 Elemental sulfur Elemental sulfur (powder form)  90.0   
 Elemental sulfur Degra-Sul (prill form) 90.0   
 Elemental sulfur Agri-Sul (prill form) 90.0

Dheck with your local nursery for either Iron sulfate or Iron chelate and sulfur

---------- FOLLOW-UP ----------

QUESTION: I was able to obtain a liquid iron treatment and a pellet sulfer product.  I applied the iron and sulfer to the area around the base of the tree to the drip line.  6-8 weeks have elapsed and I see no change in the tree.  When can I expect to see improvement?  If the products used are inadequate, and I am able to locate the products you recommend, would it be advisable to treat the tree again this fall?  Thank you!

Answer
Part of the problem will be the root ball still closely held by the wire and burlap. There is very little that can be done there except promote root growth. I would fertilize with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the trees and watered on good.
The iron and sulfur should show up next spring when the new leaves bud out.  It is difficult without a soil sample to tell just how much deficient the soil might be in iron or sulfur. So I would re apply when you do the fertilizer treatment.