Home gardeners face a variety of pest, bacterial and fungal problems when growing all sorts of trees including citrus. Every part of the tree is susceptible to a different type of problem. For instance, yellowing leaves indicate a magnesium or nitrogen deficiency that affects the health of the tree and fruit development. Check the tree frequently for defoliation or yellowing of foliage and take action immediately to prevent the problem from spreading.
Symptoms of lack of nitrogen appear on the oldest leaves of the citrus tree first. The pale-green leaves turn light to medium yellow and deepen in color before falling off. Symptoms of magnesium deficiency occur at the base of the leaf stems first. Yellow blotches spread upward if untreated, forming a V-shaped pattern on the leaf.
A citrus tree that loses its canopy due to lack of nitrogen becomes bare, resulting in a reduction of fruit production. Monitor the leaves during the growing season to ensure a healthy harvest. Lack of magnesium causes affected leaves to easily fall off the tree once they lose most of their color, specially in heavy rains or cold temperatures. The bare twigs eventually fall off in the spring. Lack of twigs affects the amount of fruit the citrus tree produces.
Conduct frequent soil tests to determine which nutrients the citrus tree is missing and correcting the problem to preventing damage. Conduct a home test with a soil testing kit or send a sample to the local extension office.
To collect samples, dig 6-inch-deep holes in several spots throughout the planting site. Remove dried leaves or plant debris from the samples and dry the soil out in the sun. Place the samples in zipper bags and send to the extension office. The results will indicate the nutrients the citrus tree lacks, revealing the culprit behind yellowing of leaves.
To prevent nitrogen deficiency, feed the citrus tree nitrogen at regular intervals throughout the year. Spread a slow-release 5-1-3 (N-P-K) fertilizer around the base of the tree in early spring, once the danger of the last frost is over and the soil has started to warm up. Water the area to ensure deep penetration of the fertilizer. Repeat the application six to eight weeks afterward. Prevent magnesium deficiency by spreading Epsom salts around the base of the tree every three months. Spread 2 to 3 tbsp. over the soil, a few inches away from the base of the tree.
Always follow nitrogen fertilizer label direction for application rates, as over-fertilizing is as harmful as lack of fertilizer. Stop feeding the citrus tree the nitrogen-rich fertilizer before the first frost so the tree becomes dormant. Prevent direct contact of Epsom salts with the base of the tree trunk.