Avocados produce glossy, elliptical darker green leaves with pale veins. Leaves stay on the tree for two to three years and show the first signs of stress caused by fungi, sunburn, over or under watering, and poor drainage.
Avocados grow best in full sun in clumps of two to three trees, which improves cross-pollination. Allow room around each planting for the tree to spread out. They don't do well in deep shade or hedgerows.
Soil must be loose with good drainage. Hillsides are better than bottom land. They tolerate a wide range of pH levels, but should not be started in plastic containers. Moist soil can cause leaves to brown and fungus infestations to occur.
Leaf damage can occur after a heavy frost. Wrap your avocados in blankets or other insulating material to reduce the stress on the tree. Bring potted avocados inside during cold weather. In hot weather, if leaves close or too many fall at once, the tree can actually sunburn.
Do not over or under water. Wet soil can cause root rot, most frequently the reason avocados fail. Water carefully during dry spells. Though drought resistant, long dry spells can cause leaf curl.
To test the soil, dig a 9-inch-deep hole and pull up a handful of soil in your fist. Squeeze it. It should hold together, but water should not drip out. If the soil crumbles, it's too dry. If it drips it's too wet.
Deep watering may help a dry tree with leaf curl, Water only once and then wait. It can take more than a week for the leaves to recover. Deep watering can also remove excessive salts in the soil which can contribute to the problem. Feed the tree with a nitrogen fertilizer four times a year. Watch for yellow leaves, an iron deficiency. Correct this with a chelated tree spray to restore missing trace elements. Allow a tree in saturated soil to dry out before watering again. For suspected sunburn, paint the trunk and branches with a 1-to-1 mix of water and white latex paint. It can take weeks before you can tell if the leaves will recover or regrow once treatment is started.