Citrus trees, with the exception of lemons and limes, need hot weather to produce their sweet fruit. Lemons and limes produce sour fruits and can tolerate lower summer temperatures as long as winters are not too cold. "Eureka" lemons (Citrus limon "Eureka") are the variety of lemons most often sold in grocery stores and grow in U.S. Department of Agriculture plant hardiness zones 9 through 10. While lemons trees, like "Eureka," can withstand cooler temperatures than other types of citrus, the trees do need full sun to thrive and produce fruit.
"Eureka" Lemons and Full Sun
Full sun is six to eight hours of sun daily. The sun allows the lemon trees to carry out photosynthesis. During photosynthesis, carbon dioxide from the air, along with water from the soil, combine within the leaves, forming basic foods required for citrus trees to live, grow and set fruit. Sun is also important for enhancing fruit color, quality and proper development. "Eureka" lemon trees that do not get enough sun produce smaller yields.
Topping Citrus and Sunlight
Mature citrus, including "Eureka," which grows to 20 feet tall and wide with a moderate growth habit, are generally allowed to grow naturally without pruning. You'll need to do some pruning to remove dead or diseased limbs and control tree size. Topping trees is a type of pruning done to control tree size and allow more sun to reach all parts of the tree, which stimulates growth and flush of leaves. Do this type of pruning before the tree grows too tall.
Crowding Citrus Trees
Proper tree spacing is important to prevent shading. "Eureka" lemon trees need to be at least 15 to 25 feet away from other trees and buildings. Crowding the trees by placing them closer than recommended can cause stunted growth and a poor fruit yield. Crowding also increases the risk of diseases, insect infestations and the need for repeated, severe pruning, which over time causes a decline in fruit production.
Too Much Sun
When pruning citrus trees, including "Eureka" lemon, removing too many branches and limbs can cause sun scald or sunburn on the tree's trunk and larger branches. Fruit and leaves exposed to direct sun in late spring, summer or early fall can experience sun scorch. Leaves affect by sun scorch appear bleached or have yellow patches, and affected fruits are discolored on the side facing the sun.