Oregon Olive Trees™

Oregon Olives 

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Oregon Olives

Oregon Olive Oil

Oregon Olive Trees

Trees for Sale

Introduction

Planting

Growing

Cultivars

Growing Olive Trees

 

Holding trees over the winter  Spring planting is recommended in Oregon.  If you happen to have bought some trees in the fall, our recommendation is to -not- plant them, and -not- to re pot them.  There is always the possibility of a harsh winter here; anything that increases the stress on the trees in the fall is likely to result in increased tree death during the winter.

 

Similarly, fruiting increases the stress on young trees, and should be discouraged.  Precocious trees (Arbequina) should have all fruit stripped off for two years after planting; all others should probably have all fruit stripped off for at least three years.  This is hard to do (I haven’t…).  After all, we plant olive trees to get the fruit!  All fruit trees seem to have a tendency to reproduce precociously in harsh climates,  here in Oregon almost all the olive trees we have planted have some amount of fruit the year after planting.  At best, this can lead to early onset of alternate bearing; at worst it can lead to tree death in an extreme winter.  See Arbequina for pictures of a young tree in a pot that this sort of debilitation happened to; see Frantoio for pictures of the fruit load even a young tree can carry.

 

Staking olive trees is not recommended by my nursery books, but almost all trees we have bought from nurseries are staked.  Trees are sold based on size; the sooner nurseries can force growth, the sooner they can be sold.  The bad news is that this new forced growth is extremely thin and weak, and in almost all cases will need to be supported for at least a couple of years.  Typically, bamboo stakes are used to support trees.  Here on the north-west side of the Willamette Valley we get a lot of wind.  I would have to say wind rub is perhaps the number one cultural problem.  To the right you can see where a single bamboo stake has rubbed three holes in a Maurino tree (and that the stake was removed and the wounds partially healed).

 

 

                          Kathy’s Grove; 03/26/09 -->

 

 

 

Below you can see where two branches used to cross, and the wind rub damage on the remaining branch to the left (the right hand branch was half sawn through with wind rub, and broke under the heavy snow loads of the mid December 2008 storms).

 

             Kathy’s Grove; 03/26/09

Pruning trees  The basic recommendation for pruning olive trees for the first five years after planting: don’t.  Olive trees are evergreen, with most of their energy stored in the leaves.  Every branch pruned off decreases the energy available for new growth (and new fruiting), just making it that much longer before trees achieve a decent fruiting size.

 

There are at least a half a dozen different pruning strategies for olives, the above “non-pruning” strategy will result most probably in a bush shaped olive tree after five years: multi trunked, relatively low growing and easy to harvest.  After five years, the pruning strategy naturally shifts to trying to open up the center of the tree and create a vase shape.  This results in what is called a vase bush tree form; very similar to the standard vase fruit tree pruning except there is not a trunk.  For boutique growers who are hand harvesting small groves for oil production, this is probably the best training system.

 

On the other hand, if you feel there is a need to prune, well then prune!  Crossing branches and wind rub is an excellent example: if both branches are going to get wind-sawn thru, why not try to save the better one and prune the least valuable one?  There is a current trend among northern California boutique growers to prune their olive trees in an almost bonsai style; if that appeals to you (and you like to prune), go for it!  The French have a very open pruning style: it is said songbirds should be able to fly thru the middle of French style pruned trees…

 

If you want to form a short trunk, say perhaps 18” maximum, to keep the olive tree a little up off the ground and (say) allow for opening a manual catch frame around the tree for harvest, I have thought of doing exactly that too!

 

Cover crops / Weed management  This is a potentially very complex subject.  There is a fairly good treatment of weed management in “Organic Olive Production Manual”, except, very mysteriously, cover crops have been almost totally neglected.  However, regardless of the legal definition you and your certifier agree to, almost any really organic (in my humble opinion!) farm plan must involve a cover crop.  So, read the chapter “Organic Weed Management in Olive Orchards” in the above book, and read what I have to say about cover crops, and decide what you want to do!

 

There are basically three different cover crop strategies used locally for growing grapes, and rather than unnecessarily reinventing the wheel for olives, let’s just consider what the local grape growers do:

 

- plant a annual cover crop in the fall for erosion control, and roto-till it under in mid spring to add organics and nutrients to the soil, and remove the cover crop competition from the vineyard.

 

- plant a “permanent” cover crop, usually of annual rye grass (which provides a tough sod for fall harvest operations, but yet is mown and dies down in the spring in order to keep from competing too much with the crop).

 

- a 50/50 solution: each year alternate aisles are cover cropped, and left for two years, such that once every two years all of the land has had the cover crop replanted.

 

For the first couple of years (and maybe forever if you are an organic grower), I recommend planting a 100% cover crop each fall (paying very close attention to the high erosion potential you are creating!), and roto-tilling it in, in the spring.  In our climate, it is relatively easy to add two tons of organic material per acre by “plowing down” the cover crop in mid-April, just about the time the olive trees start growing.  For erosion control and building biomass, winter wheat and especially cereal rye work very well.  For adding nutrients (nitrogen): field peas, fava beans, vetch, and crimson clover are all typically used in this area.  Be careful to monitor vertebrate pest populations with cover crops!

 

Kathy's Grove, cover cropped with winter wheat, 11/23/09:

This Frantoio tree has been completely girdled; note vole hole at bottom left.  It is interesting to note that the vole attack happened over a year ago, and the tree survived up to at least this past December - olive trees really are tough!  This year the cover crop will be totally removed in mid-April, and plant protectors put around the trunk of every olive tree shortly thereafter.

 

Watering  In Oregon, given relatively good deep soil (say Jory), olive trees can be dry farmed (cherry trees, filberts and grapes are all typically dry farmed on the hill our olive trees are on).  We did dry farm about 50 olive trees last year (after watering them once every two to three weeks during the summers for two years).  The well established well growing trees did just fine (say 18” of new shoot growth); however the marginal trees (say those in the “water shadow” of 50’ Douglas Firs, did not.  So, it is still recommended to deep water the trees, especially in the first five years, at least once a month during our summer drought period.  However, use your best judgment!

 

Intensive farming  Olive trees do seem to respond well to intensive farming (cultivation, fertilization, watering, etc.).  While they are very tough trees, temperate areas like ours are highly competitive (if man were to disappear, I think blackberries would take over Oregon for about 50 years).  While olive trees are in general low maintenance (as say, compared to wine grapes, which in this area are sprayed every two weeks during the growing season without fail;  I have never sprayed a single olive tree yet…), they are not zero maintenance, not if you want fruit production!  Interestingly, there are supposed to be some 5,000 acres of feral olive trees left in California, from the last olive oil boom of 120 years ago, growing slowly, ever so slowly, with fruit only at the crowns, forty feet above ground…

 

When are olives ripe enough to pick?  I get this question a lot; probably because ripeness in olives is a very confusing subject!  The bottom line is that question really gets answered with another question: "What do you want to do with the olives?"  For practical purposes, there are three different phases of ripening that are used for varying purposes, as follows.

 

Green ripe olives are most commonly used for green table olives, but are also processed and turned black for "California style black ripe table olives" (you know, pizza olives.  The marketer that dreamed up that description ought to get a lifetime achievement award for obfuscation!).  Some olives, notably Arbequina, are also used in the green phase for olive oil (Arbequina takes a heck of a long time to change color, even in California).  Another that still has excellent qualities for olive oil while still green is Frantoio.

 

Green ripe Arbequina for olive oil or green table olives, Reken Estate 11/27/09:

Good news for growers of warmth loving plants!  Hmmm, maybe we should buy the  www.OregonAvocados.com domain too!!  For the latest update, see this winebusiness page.

"Turning color ripe" olives are not very common in the marketplace in the U.S.  The best example is Kalamata table olives.  In the "old days", Kalamatas were picked ripe and water cured; but now-a-days they are generally picked "half ripe" or turning color and are processed with a brine cure.  They are then blackened (oxidized) during the brine cure to make them look like traditionally processed Kalamata (Ah!  Tradition!!  Where would we be without it?).  Even when olives have pretty much completely turned color, they are still considered to be at the "turning color" phase of ripeness (obfuscation is omnipresent these days…).  Almost all olives that are picked at this phase of ripeness in the U.S. are used for olive oil; e.g. Tuscan olives are typically picked when they are half to fully colored.

 

Turning color Leccino for olive oil or Kalamata style table olives, Kathy's grove 11/24/09:

True "black ripe" olives are also not very common in the marketplace in the U.S.  Black ripe is when not only has the skin completely turned color, but the pulp of the olive has also turned color.  This isn't commonly allowed to happen for several reasons: there is not much of a market for products made with true "black ripe" olives in the U.S. (e.g. dried salted pitted table olives); and not even California has good enough weather to get a lot of olive varieties to this stage of ripeness.  Another reason why this isn't commonly done: when olives are left on the tree past about December, they start to negatively impact next years crop.

 

When olives get to the black ripe stage, they start to lose water (and thus shrivel), which increases the percentage oil content and makes the milling for olive oil easier.

 

Pendolino olives for olive oil or Greek style table olives, starting to shrivel,  Reken Estate 11/24/09:

Alternate Bearing

 

Here is an interesting thought for you all: alternate bearing in olives may be a habit of the olive tree that growers may want to encourage in Oregon, not discourage.  Since we just don't have a lot of sunlight to feed olive trees with, for tree heath we may want to allow the olive tree to behave as it was naturally intended to, and let it alternate bear.  One year to nourish the tree, and one year for the tree to nourish us.  We, who are growing olives in Oregon, on the edge, just may not have the latitude to monkey around with the olive trees evolved ways; as much as people in, say, California can.  And that too, may be a good thing...

 

Global Warming  What is your take on “Global Warming”?  Or, much more important: “Oregon Climate Change”?  If you are planting olives, perhaps you should hope the trend is positive (hotter) for Oregon!  However, here are the “grape growing degree days” recorded at the nearest airport (KMMV, McMinnville OR,  50 degree base, 86 degree max, April 1st to October 31st, the higher the number the hotter the year):

 

                                       2004:    2318 degree days

                                       2005     2141

                                       2006     2363

                                       2007     2059

                                       2008     1983

                                       2009     2121

 

Accumulated heat improved in the Willamette Valley too:

Fertilizing  Soil testing is typically done when groves are being planned, however this is a relatively crude way to assess nutrients in crops.  Much better is to test the plants themselves: by studying the leaves; and then looking at nutrient deficient leave pictures in, say, “The Olive Production Manual” or online sources; and by “petiole analysis” (laboratory leaf analysis). This is typically done starting a few years after the grove has been established.  In California July 1st seems to be a standard time to do this (gathering leaves formed in the spring); in Oregon August 1st might then be an appropriate date for this test.  The trees then directly guide you to what they need.  In California, typically the only nutrients added on any kind of regular basis are nitrogen and potassium; boron is deficient in some soils there too.  Just remember: Oregon is not California, and hillside slopes in rainy climates are typically massively nutrient deficient!

 

Diseases  Here is the good news!  Diseases are just not a problem in Oregon!  When I first started talking to Californians about growing olive in Oregon, I was told I would have massive problems with peacock spot (Spilocaea oleaginae).  Ha!  Not true at all!  Almost none in my groves, or in other olive trees I have seen in the area.  Although the first trees I brought in from coastal California were loaded with it, it has basically died out in our climate, and has never significantly reappeared...

 

I have never seen olive knot (syringae pv. savastanoi) either.  This is somewhat to be expected, as according to the “Organic Olive Production Manual”, pg 53, it is not found in coastal California either.

 

Verticullum wilt and root rot fungus are undoubtedly present in Oregon, but I haven’t noted any particular problems with either in our groves.

 

Pests  More good news for Oregon!  The olive fruit fly (Dacus olea) is not currently present in Oregon, to the best of my knowledge.  Branch and twig borers are present here, and were more of a problem in 2009 than previously (no doubt due to the winter stress).  Olive trees are a secondary host for these insects, the preferred hosts are said to be madrone, oak, and grape.  Since our groves are adjacent to commercial pinot noir vineyards, this will probably continue to be a minor problem for us.

 

Deer have been only a minor problem for us.  Hungry deer will eat any and everything, but fortunately there are lots of cherry trees and grape vines around us, that they seem to much prefer.  The typical sign of deer damage to olive trees is to note a terminal branch that has disappeared.  Usually looking down around on the ground will reveal a “pfui” circle of leaves where the deer has spat them out.

 

As good as things grow in our temperate climate, probably the number one pest problem for us has been voles (field mice), ground squirrels and gophers.  Kathy’s Grove; 03/26/09:

Same Arbequina tree, after a deep hard freeze.  The olives are now rotting and totally unusable.  Lesson learned!

 

 Reken Estate 12/11/09:

In Oregon, as in many other olive growing regions, the end of the harvest is not dictated by olive maturity, but rather by the weather.  The olive fruit (as opposed to the olive tree) can only take about 28 F or so before becoming "frosted" and unusable.  Here are some Arbequina, about the ripest I have ever seen.  I decided to leave the olives on this tree, just to see what happened as winter progressed…

 

Reken Estate 11/24/09

Can you see the olive trees now?  At least 2 tons of dry weight organic material per acre.  Not bad!  Kathy's Grove 04/26/10:

Irrigating at 25% of that required to meet evapotranspiration throughout the entire growing season and only during midsummer both reduced per hectare oil yield by around 15%. Irrigating up to evapotranspiration cost 1 megalitre of water for each extra 10kg of oil produced.

Iniesta et al. (2009) The effects of regulated and continuous deficit irrigation on the water use, growth and yield of olive trees. European Journal of Agronomy 30, 258-265.

Comment: In Australia water is currently being traded on the open market at around $40 per megalitre – so irrigating to this extent would increase the cost of production by a massive $4 (EUR 3) per kg – aka more than EVOO is currently worth.

 

http://cesonoma.ucdavis.edu/files/27223.pdf

http://cesonoma.ucdavis.edu/files/27752.pdf

 

http://cesonoma.ucdavis.edu/files/27742.pdf