Heavy pruning of olive trees while fruiting

Question from Kathleen:
The condo complex I stay in started heavy pruning of all the fruiting olive tree today, 9-1-10. Is it healthy for the tree to be lose 80% of its leaves while developing its fruit? I do energy analysis and I thik the poor trees are in shock. Upcoming will be some heat waves that always hit in Sept. and Oct. How can I help the trees during these hard conditions when they have been so decimated?

Answer from Pat:
I can understand your dismay over seeing an olive tree stripped of eighty percent of its foliage. In most cases no tree should have more than 20% foliage removed at any one time. Nonetheless, in this case of olive trees, they will probably be fine. Olive trees are extremely resilient and they are able to withstand heavy pruning with no damage whatsoever to their health. In fact, these trees are customarily heavily pruned. The reason people prune hard in fall is to take off a lot of fruiting wood so it doesn’t make a mess, especially on pavement. Also a heavily pruned olive will develop a good shape quicker than one that is never pruned.

Olive trees live for hundreds of years in hot, dry climates where farmers sometimes cut off almost all their foliage. It is said that olive trees should be thinned out enough so that a bird should be able to fly right through the foliage and out the other side. This lets light into all parts of the tree. Italian farmers say that sun must fall on each olive every day in order for olives to be any good. Olives are also easier to pick if the foliage is not too thick. I think the trees you are worrying about will be fine and may look better eventually as a result of pruning. You shouldn’t worry too much. Olive trees do best in deep fertile soils but they can live fine in thin alkaline ones too. If you were to give the trees more water or fertilizer than usual this would be likely to harm them more than leaving them alone.

If you want you can (when no one is looking) go give each of the trees a hug and tell each one that you love it. It wouldn’t hurt the trees and it would make you feel good too. (I have hugged a bunch of trees in my life.) Or just go sit nearby and send good thoughts to them. I know this is unscientific, but it does no harm to the environment or anything else.

Comments

  1. I “aggressively” pruned a mature olive tree about 2 years ago and now it struggles with new growth on the branches but grows like crazy on the base. I continuosly strip the new growth from the base to divert energy to the branches but doesn’t seem to help much. I’m wondering if the loppers and saw weren’t “clean” and I used somehow damaged the tree….maybe best to make new clean cuts with a chainsaw (will have a professional arborist do it this time).

    • No doubt you over-pruned your tree. Pruning it even more won’t help unless you are removing dead wood. Before doing even more drastic pruning of your tree, I would try water and fertilizer to see if you can stimulate growth on the top branches. In most cases, olive trees can take hard pruning. However, that does not mean that you can cut off all the foliage or most of the foliage from branches and expect them to recover. Whenever pruning an olive tree—and this includes many other kinds of trees also— one should always leave enough green growth on each branch so the branch can continue to grow. With most trees it’s best never to take off more than 20% of the foliage. With olive trees you can safely remove 50% or even 75% of the foliage without killing the tree. You can even remove a few branches, but always leave green growth with buds so you are redirecting the energy of the tree upwards instead of downwards. The wrong idea is to aimlessly cut through branches without thinking where growth is supposed to go. The correct way is to shorten branches at joints leaving green leaves on the portion of the branch that remains so it can continue growing.

      Follow up after any pruning job with deep watering and fertilizer, washing the fertilizer into the ground with water from the hose. The most important point is that one must leave some green growth on each branch and no bare stubs, so that you can be assured that you have not killed the branch. Then follow up with water and fertilizer to help the tree to recover as one would do with any plant after pruning.

      Also, you did not specifically state at what time of year you drastically pruned your old olive tree, but hard pruning should never be done in mid-summer since summer pruning has a tendency to be followed by slow growth. On the other hand, if you want a hedge to grow slowly, then prune it in midsummer and it will recover slowly. Growth will be more rapid when you cut back a hedge in spring or fall. Another factor to consider is that any tree can suffer shock and sunburned bark from sudden loss of foliage during hot summer temperatures. I have seen many trees seriously set back and even killed from over-pruning.

      Since your olive tree has failed to grow much from higher trunk or branches for two years, it is possible that you killed portions of the top of the tree. Perhaps you back some branches into bare wood thus causing the entire branch to die. The fact that the tree is sprouting below is a sign that you cut off too many of the apical buds and thus upset the “apical dominance” of the tree. Basically you redirected the hormones (called auxins) in the tree to go back down the tree and wake up the buds located lower down on the base of the tree. Your tree now wants to die down to the lumpy crown of the tree, just above the roots. If there is still some green growth above, I would wait and give it a chance to recover. But cut off any dead wood.

      One way to discover if there is any life left in the top is to scratch the branches and trunk and see if the cambian layer is still alive. If not, that part of the tree is dead. Eventually you may have to cut off the top and choose the best new shoot or shoots from below to grow into new trunks. Cut off the others. Those sprouts down below may represent the only life left in your tree.

  2. It’s July 2012 in california central valley and we want to get our olive tree pruned. It’s supposed to be 103 this next week. The tree is 33 yrs old. Is this too much for the tree right now?

    • Olive trees are resilient and can be pruned at any time, so now is fine despite the heat. I would be more worried about the pruners than the tree. One thing to keep in mind is that by pruning in summer heat you slow down replacement of new growth, but if the olive is pruned judiciously this may be beneficial.

  3. What is the cambian layer? Is that the outer bark? And, there is also growing on most olive trees, suckers around the base, does that mean that that tree has been compromised as in your teaching dialogue?

    • The Cambium layer on a tree is not the outer bark. The cambian layer is the actively growing part of a tree that is found under the outer bark. It lies between the bark and the inner wood core of the tree. The outer bark is a dead layer that protects plants from injury and the environment, but the cambium is a live layer of tissue and as it grows it creates tree rings. It also carries nutrients and its cells actively multiply. The cambian layer also heals trees since it tries to grow over wounds to cover them and protect the core of the tree from rotting out. Many trees naturally sprout suckers from the base. This is not a sign that the tree has been “compromised”. Often it is a sign of a very resilient, strong type of tree, difficult to eradicate, since if cut down it will sprout again from the roots. Ficus, pepper trees, willows, some fruit trees and others do this. I’m sorry I don’t understand what you mean by “compromised”. Do you mean damaged or wounded? Please explain what you mean by this part of your question: “Does that mean the tree has been compromised as in your teaching dialogue?” Please explain your question including “your teaching dialogue” more clearly. Thank you.

  4. We have a very mature olive tree that is at least 30 ft tall and has about 4-5 trunks
    The issue is it is growing over the house with at least 6-8″ branches going out 20 plus feet
    It is huge and really needs to be trimmed off the house
    It is also leaning one direction and that part needs to be trim to off set the weight before breaking
    Suggestions

    • If you have ever traveled in the Mediterranean region you will notice that olive trees are pruned so that they stay low and their trunks are thick and beautiful. The branches also are pruned so they are not too long. I have a friend with an olive tree higher than her house and it has overly long branches. I don’t think it’s good looking at all.

      My advice to you is to employ a reliable pruning company and cut your tree back by 2/3 of its height and do it now. I mean cut right through the multiple trunks to dramatically lower the tree’s height. Let new growth spring from the trunk next spring. In fact due to global warming and excess carbon dioxide in the atmosphere it might simply continue to grow and sprout new growth right away. That is happening now in my garden and plants are failing to go into dormancy so, for example, when we cut an old bougainvillea almost to the ground in order to renew it, it immediately put out new growth which is now only a few weeks later, already one or two feet long.

      My advice is to remove any parts of the tree that are leaning or unsightly. Cut all the way to the thick trunk. No problem. Even cut some of the trunk away if it’s too high. Get the tree down to an appropriate height: 10 feet is enough. Look at some photos of majestic old olive trees. Then keep the new growth cut short each year. You are not going to kill the tree.

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