I like potted palms, and over the years I’ve seen palms that were off-color, sometimes even in my own house. I attributed it to an iron deficiency but didn’t know the cause. (See the reference at the end of the article for photos of iron deficient palms.)
The classic symptom of iron deficiency is iron chlorosis of the younger leaves of a plant. This chlorosis usually presents as yellowing of the younger leaves with the veins of the yellowed leaves staying a darker green. In southern Wisconsin (where I grew up) and in Dallas (where we lived for five years before coming to Maryland), iron chlorosis was common in the landscape because the soil is more alkaline than it is here. Iron binds with other elements and becomes insoluble as the soil becomes less acidic and more alkaline, and plants have a hard time absorbing it through their roots. In the DC region, you might see iron chlorosis on a rhododendron planted near the house, where the soil may be more alkaline from mortared bricks. Or, on a pin oak growing in a lawn that has been limed to make it more alkaline/less acidic to improve the health of the turf grasses. Iron chlorosis due to alkalinity is more common with plants in the ground than in pots.
It turns out that palms are quite sensitive to poorly-aerated potting soil. Being composed of mostly organic materials, potting soil decays over time, breaking down into smaller pieces and compacting, leaving fewer/smaller air spaces in the soil. With less air in the soil, the roots don’t function as well and have a hard time absorbing iron. I think every potted fishtail palm I have ever seen gets iron deficiency, and I was having chlorosis issues at home with a lady palm for several years. The recommendation is to repot your palm with fresh potting soil once a year, and don’t plant the palm any deeper than it was in the previous pot or potting soil. Ask your independent garden center for advice on the best potting soils for use indoors.
I re-potted my lady palm, totally removing the old soil. I had never done that, and I had the plant in the same soil for at least five years. After repotting, my palm greened back up over the course of a couple of months. I also switched houseplant fertilizers.
When you fertilize your palms (following label instructions, of course), I recommend using a fertilizer formulated specifically for use on palms, Jack’s Classic Palm Food. Jack’s includes iron, as well as all the other nutrients palms need to grow.
Here’s a brochure from the University of Florida, which discusses iron deficiency in palms in containers and in the Florida landscape soils. It’s the primary source for what I wrote above, and it has good illustrations.
Larry Hurley, Retired Behnke’s Horticulturist