Q. My cycad (sago palm) is yellow. I had read that it needs magnesium. What do you recommend? Sago palm (cycad) yellowing in container. A. Make sure the soil in your container drains and the plant is not watered too often. Repot or replant the sago palm when temperatures are cooler. Either wait or take it inside your house where it’s cooler when you replant and the plant reacclimates to the repotting in a week or so. Use a soil moisture meter when watering to make sure it’s not watered too often. Sometimes watering too often and poor container drainage of the soil can cause plant yellowing. Repotting sago palm (cycad) and watering as it gets hot helps cycad stay green.             Judging from your picture, your plant yellowing may be a fertilizer (plant nutrient) or watering/drainage problem. Iron shortages in plants are notorious for yellow foliage. Try applying an iron chelate to the soil when growth is first starting. Applying iron to the soil works if the plant is still growing. Once the plant stops growing then iron applications to the soil don’t work very well. There can be two reasons why nutrient deficiencies appear in soils of any kind; a shortage of a nutrient (you are suggesting a shortage of magnesium and you could be right) or the pH of the soil or its level of alkalinity. The reason I focus on iron so much is because a shortage of iron is very common to our soils and due to our tap water. Iron is probably the most common plant nutrient shortage due to our soil and tap water alkalinity. So try iron first. If that fails to “green the plant up” then try a different container soil (repot it with a different soil mix). This chart shows you the shortage of different plant nutrients with alkalinity (soil or water pH). https://extension.wvu.edu/natural-resources/soil-water/soil-testing/soil-test-nutrient-needs accessed on August 1, 2023. Putting sago palm in container in the correct landscape exposure can help.             After around June or July 1, iron applications must be sprayed on the new leaves and stems. In some cases, multiple spray applications a week apart are needed during that time. Before new growth starts in early spring, apply this same iron chelate mixed into the soil. It’s much easier. If in doubt, use an iron chelate containing EDDHA. Search for it online if you can’t find it. Magnesium deficiency, University of Florida,              Magnesium deficiency (which you suspected) is usually a speckling of leaves or fronds. It’s not usually yellowing. There is an abundance of magnesium in most of of our soils, but maybe not container soils. It is hit and miss. If you want to try magnesium (can be like whack-a-mole with plant nutrients), Epsom salts contain magnesium so apply 1 to 2 tablespoons of that mixed or the potting soil. Most plant nutrients won’t hurt the plant. Additions of boron is an exception so be very careful applying boron, chlorine or sodium. Higher levels of that can damage plants. (It is safer to repot with a different potting soil or, if that fails, put it in the ground.) After replanting, water the plant until water comes out of the bottom of the container. Even though sago palm or cycad is not a “palm”, lightly apply palm fertilizer to the soil once a year in the early spring.