European Olive Bonsai Care Guide
The Olive Tree – Olea europaea – boasts an ages-old, rich history as a symbol of peace, abundance, and glory. Dating back thousands of years, this tree has had a place of honor in not only the Bible but Homer's Odyssey as well as Roman and Greek legend. Native to the Mediterranean, the olive may reach a height of 25 feet in its natural habitat. It is a long-lived tree, with some specimens dated at 2000 years old, and more that are claimed to be as old as 8000 years.
The foliage is unique, with oblong leaves that are 1.5-4 inches in length depending on the cultivar, green on top and almost silver on the bottom, with opposite and alternating leaf structure. The trunk is grayish, developing gnarls, twists, and furrows over time, making it perfect for bonsai.
Flowering does not begin until the tree is several years old, at which point white or cream colored blooms appear on the prior year's growth, in groups of 10-40. The fruits range in size from a half inch to two inches, and colors from green to copper to deep purple.
Olea thrives best if kept as an outdoor tree in summer, and allowed dormancy in winter (below 64° F). While they are hardy enough to withstand short periods of freezing when planted in the landscape, bonsai olives need protection from frost. In order for these evergreens to retain their leaves they should not be exposed to temperatures below 43° F. The sprawling, fine root system is vulnerable to freezing temperatures. This species thrives in hot, sunny locations and should be given access to full sun in the summer. Olives tolerate hot and cold winds as well as high altitudes.
Olea europaea should not be overwatered. These trees are able to drink in water efficiently when it is available and survive when it is scarce, so don't overdo it just because the plant takes it in fast when you do water.
Feed the Olive Tree a balanced fertilizer monthly throughout the growing season, refraining from feeding in the winter. Administer two to three doses of a nitrogen-free formula in the fall (such as 0-10-10). Trace elements are beneficial when given about once a year.
Styles – this tree takes well to almost any style, with the exception of broom, formal upright, and exposed root (the delicate feeder root system makes this style an unwise choice).
Heavy branch pruning can cause unpredictable results in this species and shortening a branch may cause dieback all the way to the trunk. Pruning of thick limbs during the growing season can cause coarse, congested growth at the cut site. This can potentially result in inverse taper if not kept under control. If thicker branches must be pruned, try doing so in late fall or winter when growth is slower, then rub off any undesirable buds as they appear at the trunk. Remove new shoots from branches early in the tree's life in order to encourage thickening.
Pinching new growth during the growing season will cause back budding on the whole tree. In order to encourage ramification pinching should be done between temperatures of 50 and 100° F. When pinching is only done between those temperatures, it encourages smaller leaves and short internodes. Remove any buds that are growing straight up or down from the branches.
New growth comes in as green turning to purple, then tan. Pinching green shoots will produce less ramification than purple or tan. On younger trees, pinch back to one to three leaves when growth is purple or turning tan. For older trees on which ramification is more developed, pinch shoots when green or turning purple.
Wiring should only be done if absolutely necessary, due to the delicate, brittle nature of the wood and bark. If a tree is under three year's old, wire carefully in late fall or winter. Use raffia on older trees to minimize damage to the branches. Landscape olives often have deadwood, however olive wood rots readily so if you have a collected specimen the deadwood should be treated with hardeners or lime Sulphur.
Olea is best propagated by cuttings as seed is unreliable, often resulting in low germination rates. For cuttings, take semi-hardwood, 4-6" long cuttings in late spring or early summer. Pinch off all leaves except the top 2-4 sets. Rooting hormone is beneficial for rooting the cuttings. A mixture of 90% perlite or sand with 10% peat moss is a good medium. Keep the cuttings misted, avoiding soaking them. Bottom heat will increase the success rate significantly.
Young trees can be repotted every two or three years, in the spring. Older trees can usually go longer. Prune up to one third of the root ball, avoiding fine feeder roots where possible. Olive trees tolerate most soil types, though they prefer slightly alkaline soil. A small amount of lime may be added, and there should be a high ratio of inorganic matter.
Insects/Pests & Diseases
Aphids, mites, and scale are potential pests on this bonsai. It may also fall victim to leaf spot or olive knot (due to the bacterium Pseudomonas savastanoi). Examine your bonsai regularly for problems.