How can we save our sagos?

Question

We have 15 sago palms in our front and back yards and another 5 in large planters. They are all over 10 years old. I’ve never had any problems with them. I’ve been fertilizing them about twice a year with general palm food and they receive regular watering with the sprinkler system (two 5-min. waterings per day, 5 days per week). I have been trimming the lower fronds as the new fronds open up and spread out. About 6-8 months ago, several of the oldest ground plants started to dry up and their new fronds do not open up completely and eventually dry up. This happened at the same time to our most prominent plants in the front yard and since then it’s been happening to several others both in the front and back yard.

The potted palms seem to be ok. I have both increased and decreased the watering amount to see if there was any change. Based on the advice of a local nursery, I have applied Vigoro Palm, Ixora and Ornamental Food (8% nitrogen, 4% phosphate, 8% potash, 1.1% magnesium, 3% sulfur) two times over the past four weeks. I haven’t noticed any change. I purchased Epsom salts yesterday as recommended by your website but before I apply it I wanted to see if you have any suggestions on saving these beautiful plants that look like they are on their last days. We are in the central valley of California, which was desert 100 years ago before the aquaduct system was put in. Soil is mostly sandy loam.

Answer 1

Once a month would be a recommended fertilizer schedule.
I do think this may be a nutritional deficiency, so Epsom Salts can be beneficial.
I myself use it on my plants with good results.

https://www.gardeningknowhow.com/ornamental/trees/sago-palm/how-to-care-for-sago-palms.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/epsom-salt-gardening.htm