Is is beneficial to add MnSO4·H2O to yellowing and or browning Sago palms during the winter?
Adding Manganese Sulfate to Sago Palms.
Certified GKH Gardening Expert
Adding manganese sulfate will probably help your sago palm. However, it is best to wait until the sago palm is actively growing in spring to apply the fertilizer, since it won't benefit from it when it's dormant. If you do see your plant growing during winter (putting out new leaves or expanding small leaves) then it is fine to add the fertilizer then.