Washingtonia palm trees are beautiful, large-fan palms that grow readily in (and are a common sight in) California, Florida and other warm, sunny states with typically mild winters. These palms grow quickly and can become up to 100 feet tall, especially if you care for them properly--this care includes regular fertilization. These palms will usually continue to grow, even if deprived of good fertilizer for a time; however, you’ll get a stronger, much more beautiful palm tree through feeding it.
Mix a liquid, all-purpose fertilizer with water in a clean garden sprayer (use one that has not been used for weed killer or pesticides), diluting it to half-strength with water as recommended by a University of Oklahoma website. If you use a palm tree fertilizer instead of an all-purpose fertilizer, just follow label directions regarding dilution.
Spray the fertilizer on the soil (unless the palms are still in pots) about a foot away from the trunk, all around the palm tree. If the palms are still in pots, simply spray the mixture onto the potting soil.
Repeat this process once a month. Write the fertilizing date on a calendar so you know when fertilization is due next.
Apply a granular, slow-release palm tree fertilizer around the base of the tree (not directly on the trunk--about 1 foot out). Follow directions on the label regarding how much of the fertilizer to use (it will depend partly on the size of the palm tree).
Water the granules into the soil with your garden hose. This helps prevent them from blowing away in the wind or washing away from the tree if it rains heavily before the granules sink a little into the soil.
Repeat this slow-release fertilizer application the next spring. No other fertilizing should be necessary.