I have 2 calamondin orange trees and 1 Meyer lemon tree, all in pots. I went to a nursery and asked about when to fertilize them and the lady said early fall (right now) is fine. She said about 1/2 cup per tree will work. I'm not sure how old my trees are. The young orange tree is probably less than a year and has not flowered yet. The other, maybe 2-3 years and has 50+ fruits on it currently. The Meyer lemon tree is probably 2-4 years old and is currently flowering. I fertilized them last night, keeping the fertilizer away from the trunk. Today we got a really heavy rain while I was at work. When I got home several of the leaves on the lemon tree were brown, wilted, or had fallen off. The young orange tree was the same but not as bad. The older orange tree with the fruits, however, looked perfectly fine. I removed as much of the fertilizer from the 2 trees that it negatively affected and I rinsed them off well and repotted them, hoping to separate them from as much fertilizer as possible. Any further suggestions that you could help me with on how to avoid this in the future and how to properly care for my trees?
Hancock County Mississippi
Container-grown citrus do need fertilizer throughout the year for good growth and fruit production, because the act of watering leaches fertilizer out of the pot.
Not all fertilizers are equal. Some work quickly, others very slowly. Quick-acting fertilizers--any synthetic fertilizer that is not coated for slow release--have a higher potential for burning plants with symptoms like you describe. Other forms of fertilizer, like fish emulsion, bone meal and slow-release synthetics (Osmocote, for example), are either very low analysis or slow reacting or both.
A 1/2 cup of fertilizer per week recommendation of fertilizer sounds like a lot, depending on the fertilizer. It seems you took the appropriate steps to eliminate an overdose of fertilizer. From here forward, I suggest you look for a slow-release fertilizer. They vary in analysis (example 15-6-12) and release curve (3-month, 5-month). Apply to each of your container citrus plants according to the product label rate and recommended frequency. This is typically about every 3-4 months.
It is understood that you will need to protect your container citrus in the winter by moving them to a protected shelter. Otherwise, you should allow the fertilizer to diminish as you approach the fall of the year, to slow the rate of growth and help it survive the winter better. If you protect your citrus plants properly in the winter, then maintain a year-round fertilization program.