The Care and Feeding of Olive Trees02/09/2015
Olive trees require a well-drained soil and a sunny position. Avoid sites where water stands during rainy periods or where ground water seeps into a hole two feet deep. Do not, however, confuse the olive for a desert plant. It needs regular watering to thrive. Insufficient water will cause your tree to suffer, and even die if left too dry for too long.
Choose a site that receives at least six hours of direct sun per day. Full sun is ideal.
Plant your tree at the depth it has been growing in the pot. Do not amend the soil with organic material, moisture-retaining polymers, fertilizer or anything else. Simply plant in the native soil (provided it is well-drained) and backfill with the same.
If your tree requires staking, it will already have a stake in the pot. A very young tree may require a heavier stake as it grows. Once the trunk caliper reaches 1.25 inches or more in diameter (or perhaps less for shrub-form or short trees), it will no longer require a stake. Until then, use a stake large enough to hold the trunk upright. Put the new stake in the same hole the previous stake occupied and tie the tree to the stake with arborists' tape such as comes with your staked tree. Do not use wires, water hoses, cloth, cables, guying systems or other means of securing your tree. A good stout stake and the proper tape is all you need.
Olive trees do not need special olive tree fertilizer but results will be exponentially more satisfactory with a good nutrition regimen. If planting is done after mid-August but before March 1, do not fertilize at the time of planting; wait until spring. Otherwise, fertilize after planting and regularly throughout the growing season. How regularly will depend upon the type of fertilizer used. We at Olive Tree Growers prefer to use a premium slow-release fertilizer with essential minor elements (zinc, boron, calcium, etc.). Use a fertilizer that has a nitrogen analysis of at least ten percent. Olive Tree Growers believes that some sort of minor elements package is important, as many soils are lacking in some essential minerals which aid plant growth in several ways.
A fast-release farm-type fertilizer such as 10-10-10 or 13-13-13 may be used according to label directions. Many such fertilizers contain some minor elements and are widely available. Be sure to water very well after application. These fertilizers are generally not for use on plants in pots.
Liquid fertilizers may be used (again, a formulation with minor elements is best) but it should be remembered that liquid feeding is a fleeting thing and must be repeated often.
Organically-derived fertilizers are available and a good thing, though often more expensive and rarely contain the percentage of nitrogen preferred by olive trees. Top dressing with organic material such as composted manure or kitchen compost can be done but the grower should consult the current literature. It can be difficult to achieve a good balance of nutritional elements by this method. It is environmentally responsible but requires more study and understanding by the gardener. Always avoid placing compost or any fertilizer next to the trunk of the tree.
Whatever type of fertilizer is used, it is best to feed lightly and often during the growing season. Avoid heavy applications of fast release fertilizer that could damage plants and leach or run-off into groundwater. Always read and follow label instructions. Do not fertilize after mid-August or before mid- March unless you live in a very warm climate.
If your tree is planted in a lawn area, take care that lawn maintenance practices do not harm the tree. Do not allow "Weed and Feed" products to be used within 30 feet of your tree. These products are designed to feed lawn grasses and destroy other plants. Remember that the roots of any tree extend far beyond the drip-line of the branches. Also, do not allow weed-eater operators near your tree. Weed-eater operators kill thousands of trees every year by "girding," or removing the bark from the bases of trees.
Wood chips are bad, okay? Do not use wood chips, cypress mulch or any cellulose product for mulch. These products are high in carbon and rob the soil of nitrogen and other nutrients in the decomposition process. They also hold too much water in wet periods and, once dry, shed irrigation water and rainfall like a shingle roof. We prefer to use only pine straw for mulch and keep it back several inches from the trunk; do not allow a build-up of decomposed mulch around the base of the tree trunk. If pine straw is not available, you can mulch with pine bark or gravel.
Once established, olive trees are among the most drought-resistant trees in the world, but porous soils such as Florida sand are very inefficient at retaining moisture; olive trees in sandy soils must be watered often. You will have to water sufficiently to get your tree established and thereafter as necessary during dry periods. No one can give you a formula for that; you will have to observe and evaluate. Low volume spray irrigation can be used effectively, but drip irrigation is of little or no use in sandy soils.
Olive trees do not require pruning in order to produce fruit, at least not until they are around 50 years old. It is okay to prune olive trees to achieve a desired shape but remember that they fruit on branches that grew during the previous spring and summer; cutting off a lot of such growth will preclude or greatly reduce fruiting potential for the next season.
It may be helpful to prune the top, upwardly growing, branches back by a few inches to encourage lateral growth, thus facilitating the picking of fruit. It is also a good idea to cut out small interior branches that will ultimately clutter the tree's appearance and provide protection for any pests or diseases that may be lurking around your site.
If fruiting is not important, you can shape your olive tree to any way you please.
The only pests we have known to attack olive trees outside of olive producing regions is an armored scale insect. It is not common but should be watched for, especially if your site has other species prone to harbor scale insects. Inspect the trees by looking under the leaves and in the branch axils for a dark bump the size of a "BB." These insects do not move in the adult stage; they attach themselves like barnacles. The presence of sooty mold on leaves and bark, or ants crawling on your tree, indicates the presence of scale insects.
If scale is found, it may be treated with a variety of products, depending upon personal preference. It may also be removed by hand if you have only one or a few trees. If you have other plantings that attract pests such as thrips or stink bugs, these may also have a go at your olive tree. Consult your local garden center or pest control specialist about the control of pests. Regulations vary from place to place.
Finally, be sure to keep ant colonies away from your trees.