Answer: Sago Palms are very tough plants, but sometimes the leaves can turn yellow or brown, and many things can cause this to happen. The pattern of the yellowing gives the best indication of the problem.
PATCHY YELLOWING OR BROWNING ALL-OVER, GENERAL YELLOWING OR BROWNING
TOO MUCH SUNLIGHT--Sometimes Sagos will develop a light yellow or white "bleached" color. This is most likely due to being placed in too much sun. Sagos can be grown in full sun, but they need to get acclimated to it. The best thing to do is leave it right where it is. It's just like a Ficus Tree--if you move it, the leaves fall off, but it grows back just fine. The same thing for a sago in full sun--the leaves may burn a little, but it will grow back just fine.
BRUISING--Sometimes Sagos will develop brown areas on the leaves because they were bruised in shipping, or are in an area where the leaves suffer from bruising caused by the wind or people or animals brushing against them roughly.
INSECTS OR DISEASES--Yellow spotting can be caused by insects or diseases attacking your plants. Look on the undersides of the leaves to find any harmful critters.
OVERWATERING--Overwatering is the most common cause of a general-overall yellowing of the plant. You may not even notice it until it's too late, because it will be a gradual process. Sagos are very tough plants, but overwatering will cause the roots to rot, and will kill the plant. Let the soil dry out between waterings, or keep it slightly moist all the time, but don't let the soil remain soaking wet for more than a few hours just after you've watered. You shouldn't need to water more than once every 5 to 7 days, even in hot weather.
UNDERFERTILIZING--This is especially a problem in colder months, even though you may have applied fertilizer to your plants. As the soil temperatures drop, the tree's roots have a hard time taking up elements. So, even though there may be plenty of fertilizer in the soil, the plant may not be getting any. It is commonly seen on palms in the winter. The best thing to do is wait for warmer temperatures.
SHOCK-- Sometimes the plants will go through a period of shock, especially if you put them in an area where the conditions are very different from where they had been previously growing. If the lighting in the store was very dim, and you place them in full sun, your plant is probably going through shock. This can cause the leaves to turn brown or yellow, develop brown or yellow spots, or it can cause the leaf tips to curl.
OVERFERTILIZING--Whatever brand of fertilizer you choose to feed your plants, follow the manufacturer's instructions on the label. In the case of fertilizer, more is not necessarily better. The mineral salts in fertilizer can build up inside the plant tissue, and burn the leaves. This usually occurs at the leaf edges first, and moves inward toward the midrib of the leaf. The leaves will turn yellow first, followed by a brown color.
Hope the above information helps you determine the cause of yellowing on the leaves of your Sago.
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