Sago palms are not true palm but a prehistoric form called a cycad, which develops seed cones instead of flowers and has uncurling, fern-like foliage. Sago palms are slow-growing and can range from 3 to 20 feet at maturity, depending on the variety. Cultivating them requires a little special care. If your sago palm isn't as green as it could be, address factors in its environment that hurt its growth.
Fertilize sago palms regularly. Use a palm fertilizer with equal parts nitrogen and potassium, with magnesium and manganese. Apply twice a year at a rate of 1/2 lb. per 2 feet of trunk.
Test the soil drainage. Pour a bucket of water over the root zone of the palm. If the water doesn't soak in immediately, amend the soil with equal parts peat and sand to a depth of at least 3 feet to improve drainage.
Look up. If other trees are shading your sago palm too deeply, cut them back to let in more light. Sagos need at least six hours of full sun per day to stay vibrant and green. Deep shade can eventually cause the palm to stop producing new leaves. Conversely, sago palms shouldn't be planted in full midday sun. Too much light and heat will also cause yellowing and dieback.
Check leaves for a whitish, dust-like appearance. Aulacaspis cycad scale is an insect problem for sago palms and can turn foliage white in a matter of days. Dislodge these insects with a hard stream of water from a garden hose, and follow with a spray of insecticidal soap, following directions on the package for the size and area of foliage to be treated.
Look at the top of your sago palm. If it's developing a brownish, frizzy appearance, it may have a serious manganese deficiency. Apply magnesium sulfate to the soil, getting the correct proportions for the size of the tree from the package instructions.