Several factors can cause fruit to drop from citrus tree

Aloha Nick, I have a lime tree that’s about 5 or 6 years old and about 5 feet tall. Each year it flowers profusely and even has little limes the size of peas on them but then they all fall off and we are left “limeless.” We have other citrus fruit trees such as tangerines, lemons and tangelos in the same area which bear lots of fruit so I can’t understand what the problem is. We live in Sunrise Estates Subdivision in Hilo and fertilize regularly with a palm/citrus fertilizer and also use a soap water solution to keep the bugs down. I hope you can help with this. — Mahalo, D.U.

In most cases, less than 5 percent of citrus blossoms will actually develop into mature fruit. An overwhelming number of the blooms naturally drop from the tree during bloom and shortly thereafter. This is a natural thinning process. Once the tiny fruit has reached about 1 inch in diameter they tend to stay on the tree. After this point, continued fruit drop is due to some type of environmental stress. There are several possibilities: vog, nitrogen deficiency or excess, sudden high temperatures, a lack of water, too much water, heavy pruning, a heavy insect/mite infestation, hot dry winds, and lastly, constant rain during the bloom period. Any one of these factors that occurs around the time of bloom can cause the flowers and young fruit to drop.

One pressing question is, why is the lime dropping fruit but not the other citrus trees? Here are some of the more common answers: 1. We are dealing with different citrus varieties and therefore different genetic compositions.

Consequently the various varieties will react differently to the numerous stresses; 2. In the same manner, citrus trees are normally grafted or budded onto different types of rootstocks, and these various rootstocks react differently to the many diverse environmental conditions; 3. And lastly, although difficult to observe, some locations in the backyard may be more conducive to plant growth: better soil drainage, more nutrients or more protected from dry wind and high temperatures.

Hello, our lime tree is looking sad, after years of bounty. We have donkey manure and bio-char from Kawaihae Carbon. Are these good for lime trees? The tree gets irrigated three minutes every six days in desert (Kawaihae) conditions. Any suggestions will be appreciated. — Mahalo, Susan

In general, donkey, cow or sheep, horse or rabbit manure are all useful fertilizers for a lime or any other tree. Caution: In dry climates, similar to places in California, an abundance of manure over time causes a buildup of salts. The salts would then need to be leeched with irrigation since they would be detrimental to the tree. In wetter climates heavy rains will wash the salts away.

Looking at your watering schedule, however, the problem appears to be not enough water. Here is an easy way to test soil moisture: dig about 3 to 6 inches below the surface, and actually feel if it is moist. When citrus trees are lacking in water, their leaves tend to curl or fold together but not like the curling caused by aphids. To help conserve moisture apply a layer of mulch around the tree but not against the trunk. During a drought, trees that have been mulched fare much better than those without. An application of mulch is also useful in wet climates for a variety of reasons, especially in times of drought.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.