Olive bonsai

Placement

The olive is an outdoor tree emblematic of Mediterranean countries. During the growing season, give it full sun: direct light drives growth and reduces leaf size, which is exactly what bonsai growers want. In summer it can stay in the sun all day, but a little afternoon shade helps it through intense heat.

The olive tolerates temperatures slightly below freezing, but it must be protected from harder frost, which damages the branches. The best winter home is a cold greenhouse or a bright room kept frost-free. Avoid a heated room in the house at all costs: there it lacks light and suffers from dry air, which makes it highly susceptible to scale. In spring, do not move it back outside until all danger of frost has passed. Stand the pot on pot feet so excess water drains away freely.

A vigorous olive is rarely attacked. Scale and mealybugs appear mostly on a tree overwintered too warm: improve its growing conditions and treat with a suitable product. Fruit flies and borers can also attack it, and the most common disease is olive scab, also called peacock spot. The olive plant profile covers the tree in the ground, its hardiness and its origin.

Soil mix

Olive needs a very free-draining mix with a slightly alkaline pH, ideally between 7 and 8. A mix a little more water-retentive than for other species suits it: for example, two parts akadama to one part lava rock and one part pumice, with a medium particle size for medium and large trees and slightly finer for very small bonsai (shohin).

Akadama, a fired Japanese clay, should be sifted before use to remove dust; it breaks down after about two years, which is one reason to repot regularly. Pumice holds water and nutrients while helping the roots branch, and lava rock adds structure and drainage.

Watering

Olive prefers being kept on the dry side rather than wet. Water thoroughly when the soil surface becomes dry, then wait for it to dry again; avoid constant wetness. There is no fixed schedule: during the growing season, check the pot morning and evening, because a tree in full sun can need water every day. In winter, in a cool room, check it daily but expect to water only every several days, depending on the climate and the tree. Good-quality tap water is fine. Do not mist the foliage, as this encourages leaf burn and disease.

Fertilizer: during the growing season, apply solid organic fertilizer every four weeks or liquid fertilizer every week. You can also match feeding to the tree’s stage. A young tree in development gets a high-nitrogen fertilizer from early spring to the end of the season to build size and vigor. A refined bonsai is better served by a mild, lower-nitrogen organic fertilizer, applied only after the first or second flush of growth has hardened off, so the leaves stay small.

Pruning

Olive responds vigorously to pruning and buds even from old wood.

• Structural pruning: make heavy cuts in late winter; the tree responds with vigorous growth the following spring.
• Maintenance pruning: in spring, let the new shoots extend until they harden off, then cut them back to two leaves, or to one or two pairs of leaves. Next, let the secondary shoots reach 6 to 8 leaves before cutting them back to two, and repeat throughout the season.
• Partial defoliation: on a very healthy tree, at the time of that first pruning, remove 80 to 90% of the leaves from the outer canopy. The tree pushes a second flush with smaller leaves, which increases ramification within a single season.
• No pruning in fall: it would trigger growth that cannot harden off before frost, and the twigs would die back.

Styles: the gnarled trunks, rough bark and heavy, hard deadwood of cultivated olive suit trees with a very aged look; it is also grown in cascade style. Wild olive, or oleaster, and its Mallorcan form known as ullastre have tiny leaves, short internodes and finely striated deadwood. Oleasters collected from the wild (yamadori) often carry striking natural deadwood.

Wiring

Young branches and new shoots can be wired at any time. The two best periods are winter and late spring, right after partial defoliation, when the structure is easy to see. In winter, avoid heavy bends, which often cause twig dieback the following spring.

Choose aluminum wire, which is gentler on the bark, about one third the thickness of the branch and wound at roughly 45°. On olive, wire usually has to come off within one to two months so it does not bite in; the tree can be rewired several times a year. Cut the wire at every turn rather than unwinding it. Old branches are stiff and brittle: to lower them, use guy wires anchored to a strong root or to the pot, protecting the bark where the wire attaches. If you still want to wire a thick branch, a wrap of wet raffia limits the damage.

Repotting

Repot every two or three years in early spring, as the buds begin to swell; old specimens can wait longer. Remove about a third of the roots. Olive is robust: you can remove all the old soil without weakening it, and it even tolerates very severe root pruning, though that is best avoided. Use the alkaline mix described above.

Propagation: olive is propagated from seed and cuttings.