A sago palm tree that turns yellow or develops yellow splotches likely has a manganese deficiency. Sago palms that have this deficiency show yellow spots or completely yellow leaves, and as the leaves die, they look frizzled and turn brown. Failure to address this deficiency eventually kills the tree.
All plants need manganese for healthy, normal development, and the best soil pH for manganese absorption ranges from 5.5 to 6.5. However, some regions have soil that is deficient in manganese or a pH significantly higher than 6.5. The first step to address this deficiency is soil testing, which country agricultural extension offices handle upon request.
Manganese sulfate is the preferred soil supplement to address this deficiency, and nurseries, home improvement stores and garden centers generally carry it. Manganese sulfate and magnesium sulfate (Epsom salt) are easy to confuse, but adding Epsom salt to the soil has a disastrous effect on plants.
The necessary manganese sulfate amount to correct the deficiency varies with the size of the tree, the type of soil and the soil pH. Sandy, acidic ground does not need as much supplementation as soil with a higher pH. For example, a small tree in ideal soil only needs an ounce, but an extremely large tree in soil that is high in pH may need as much as 5 pounds. Spreading the supplement needs to be even and cover the entire root zone; after spreading, it is ideal to add a half inch of water to the root zone to soak the manganese sulfate into the soil.