Defoliating Olea

By Rudi Adam

To start with, a word of warning!!! Do not defoliate trees when they are sick, under-nourished or out of their natural growth-cycle!

Should you do it?

In normal circumstances it is rare that evergreen trees are defoliated, but under natural conditions it may occur now and again, usually through insect infestation or drought. Let us examine the conditions of those occasions when it may be appropriate.

  • The foliage is too large

If the foliage is too large one needs to examine the cause. Was fertilizer of the wrong composition used? Too much nitrogen in the fertilizer may cause larger than normal foliage.

A soil-mix with a high content of compost will have a similar effect. Watering too much or too often, causes excessive growth. All of these conditions will also cause extended inter-nodal distances. It will not only manifest itself in excessive and large foliage, but also attract every insect to this haven of greenery.

  • The foliage is damaged

If the foliage is damaged by insects, such as lacewing or thrips, hail, sunburn or it has suffered from drought, one might as well remove all the remaining leaves soon after the event, so that the damage is arrested.

  • The tree is growing too vigorously

If the tree is growing too vigorously, which may occur in newly collected trees or trees that were recently repotted the tendency of producing larger than normal leaf-size may occur. Fertilizing and placing the tree in a too shady area may also cause excessively large foliage.

  • The tree has naturally large leaves Since oleas are on the whole grown from seed, they may vary considerably not only in shape, but also in size. Besides this, different regions may have there own habits (clones). Some regions produce straight foliage others a wavy foliage. Under these conditions the foliage should be pruned or the tree defoliated.

When to do it

If you have a choice in the matter, there are three ideal times:

Early spring - August to September

Mid summer - December to January

Autumn time - April to May

How to do it

First give the tree a good hair-cut by removing the excess growth, be that in length or in the pile of foliage, but remembering that in no time the new growth will add between 5 to 10mm. Then cut as close to the base of the leaf leaving as much of the leaf-stalk (petiole) as possible taking care not to damage the dormant bud. Remember that the leaves of olea grow in a left right as well as up and down pattern. The left - right pattern is largely used to elongate or fill out the branch-pattern and the up-and-down buds are used for increasing the physical size of the tree.

How often to do it

On newly trained trees defoliate a maximum of once per year. Remember that this procedure also slows the potential root development.

On established trees it is possible to do leaf pruning, provided the tree is in a healthy state, twice per year, but never in succeeding seasons i.e. autumn and spring or alternatively summer and spring. Before defoliation the tree needs to be fertilized with a low nitrogen fertilizer about a month before the procedure. Trees suffering from root-rot (Phytophtora) should never be done as they are in a weakened state and will only produce larger foliage to obtain more nourishment.

Why to do it

Defoliation is used to increase foliage mass and reduce leaf size as well as to increase the amount of twigging.

How to avoid it

Fertilize with low nitrogen fertilizer, reduce excessive watering during the active growing period, prune frequently after the emergence of new foliage and place trees in a sunny area and follow a spraying program for insects.

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Tenderly, lovingly

raking up dead leaves

in his Bonsai forest

Random Bonsai Tip

So much time is spent on striving towards perfection in the foliage area of trees but little contemplation goes into the area around the nebari. Consider planting your tree at different heights in the pot which might enhance the existing taper and roots. If your tree lacks roots use moss mounded in such a way to suggest underlying roots, or you can even use sticks of similar appearance to the wood of the tree as 'fake' roots until you are able to coerce roots to fill the void. Use appropriate gravel to complete the scene.