Published in the Contra Costa Times on May 1, 2004

Q. My lemon tree is losing a lot of leaves.  Should this be happening? I have lost much of my fruit in prior years. What can I do so that it stays on the tree?

A. Lemons are one of the varieties of citrus commonly grown in home gardens.  Citrus are sub-tropical, evergreen trees, with foliage that will stay on a tree for 2-3 years. The leaves are replaced continually, although the heaviest loss occurs during flowering, which throughout most of this area occurs in the spring. Our weather warmed up very early this year, which the sub-tropical citrus enjoyed, and blooming has been prolific. The leaf loss is normal.  Except along the coast, citrus stops growing in the winter and starts growing in February- March when the weather starts to warm up and the days get longer. There are other factors which can influence leaf drop, including high temperatures, wind, low soil moisture, low humidity and pest problems. The weather we have been enjoying has probably been influential in the leaf drop you have been experiencing.

Lemons are blooming prolifically now, but be prepared that most of the flowers and young fruit  drop off under normal conditions. It seems that a combination of environmental and physiological factors determine which of the fruits will persist to harvest. High temperatures from mid- May through mid-July cause the young fruit to stop growing and to abscise (fall off). Nutrient deficiencies can also cause fruit drop. A soil test can tell you exactly what you have and what you might need to add to the soils where the Lemon  is planted. Most of the soils in this area are deficient in nitrogen, and possible zinc (this is specific for citrus crops), and may need yearly supplements. Occasionally manganese, potassium or iron need to be supplemented as well. Nitrogen levels are critical for fruit set and retention in the spring. Nitrogen is available in many different forms from your local nursery, both in organic and in-organic forms.

 A general guideline to fertilizing follows: Young trees less than 4 years of age need 2T of nitrogen spread under the tree prior to irrigation 3-4 times a year.  By the third year this amount should be doubled. If using organics, about 1 gallon of good composted manure can be mixed with the soil under the tree. Be aware that manure are often high in salts. Mature tree will need 2-3 lbs. of actual nitrogen a year scattered under the canopy and several feet outside of the drip-line.

To calculate the amount of nitrogen the first number in the parenthesis following the fertilizer name is the percent nitrogen in the fertilizer. For example, ammonium sulfate (21-0-0) has 21% N. Therefore, for every 5 lb of ammonium sulfate applied, the tree receives 1.05 lb of actual nitrogen.

Here is a list of fertilizer formulations and the amount needed:

5-10 lb. per tree of ammonium sulfate (21-0-0) = 1 to 2 lb. actual N

3-6 lb. of ammonium nitrate (33-0-0) = 1 to 2 lb. actual N

2-4 lb. urea (46-0-0) = 1 to 2 lb. actual N