The Q&A Archives: Avocado trees

Question: I would like to know everything about avocado trees. Climate, how much cold they can take, and the best way to grow them at home.

Answer: Avocados will grow in shade and between buildings, but are productive only in full sun. The roots are highly competitive and will choke out nearby plants. The shade under the trees is too dense to garden under, and the constant litter can be annoying. Give the tree plenty of room--up to 20 feet. The avocado is not suitable for hedgerow, but two or three trees can be planted in a single large hole to save garden space and enhance pollination. Once established the avocado is a fairly tough tree. Whitewashing the trunk or branches will prevent sunburn.

Avocado trees like loose, decomposed granite or sandy loam best. They will not survive in locations with poor drainage. They are tolerant of acid or alkaline soil.

Avocado trees may not need irrigation during the winter rainy season, but watch for prolonged mid-winter dry spells. Over irrigation can induce root which is the most common cause of avocado failure. To test to see if irrigation is necessary, dig a hole 9 inches deep and test the soil by squeezing. If it is moist (holds together), do not irrigate; if it crumbles in the hand, it may be watered. Watch soil moisture carefully at the end of the irrigating season. Never enter winter with wet soil. Avocados tolerate some salts, though they will show leaf tip burn and stunting of leaves. Deep irrigation will leach salt accumulation.

Begin feeding young trees after one year of growth, using a balanced fertilizer, four times yearly. Older trees benefit from feeding with nitrogenous fertilizer applied in late winter and early summer. Yellowed leaves (chlorosis) indicate iron deficiency. This can usually be corrected by a chelated foliar spray of trace elements containing iron. Mature trees often also show a zinc deficiency.

It is important to choose a cultivar that is hardy in your area. Mexican types are the best choice for colder regions. Plant above a slope for air drainage, or near the house for added protection. In youth, protect with rugs, towels and such spread overhead on a frame. For further protection heat with light bulbs and wrap the trunk with sponge foam. These measures also permit tender cultivars to become established in borderline locations; established trees are much hardier than young ones. The upper branches can also be top worked with hardy Mexican types, which will protect a more tender cultivar on lower branches, as well as serving as a pollinator. Harvest fruit before the frost season begins. Cold-damaged fruit turns black. Avocados are often in bloom at the time of frost and the flowers are killed, but the tree tends to rebloom. This is especially true of Mexican types.

Columnar cultivars require pinching at early age to form a rounded tree. Others need no training. The skirts of avocado trees are sometimes trimmed to discourage rodents, otherwise the trees are usually never pruned. Branches exposed to sun by defoliation are extraordinarily susceptible to sunburn and will surely die. Such branches should always be whitewashed. It is better to avoid any pruning.

The hardiest hybrid avocados will endure temperatures of about 26F so if your garden regularly receives frost, choose a hardy hybrid.

Hope this answers all your questions about growing avocados!

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