Planting & Growing Info
Fertilizing an Olive Orchard
The fertilizer requirements of an olive orchard are not complex. Traditional fertilizing has always been simply done with natural well rotted manures and mulches. This method ensures that all nutrients applied are readily usable by the trees. It also reduces the possibility of over fertilizing which can have detrimental effects on the trees, the soil, and the underlying water table.
Olive trees are 'natives' of the Mediterranean countries and therefore they should be treated as such even when introduced into far off lands such as California and other parts of the US. They're similar in their cultural needs to trees such as eucalyptus. In light of this, regular or large applications of chemical fertilizers will do more harm than good. Controlled chemical fertilizing can produce good crops, however it must be carefully monitored to ensure no damage is done.
There are many manures which are perfectly suitable for olive orchards. The one rule which must be kept in mind is that no matter which manure you choose or have access to, it must be well rotted before being put onto the orchard. Due to their acidity, fresh manures can burn the roots of the trees. For information on fertilizer requirements at planting see our page on Planting.
A manure which we use as an example and recommend due to its well rotted and balanced nature is that found in meat chicken sheds. The floor of the shed is covered with a layer of sawdust prior to the chickens arriving. The chickens then spend a number of weeks manuring on and scratching around in this sawdust as they grow. After the grown chickens are removed, the well mixed sawdust and manure is removed from the shed and heaped into piles. This product is ready to be placed on the olive orchard. (NB. You cannot reproduce this product simply by mixing one ton of fresh sawdust with one ton of fresh chicken manure as both ingredients must be well rotted prior to reaching the trees).
Well rotted manure from horses, cattle, pigs and sheep etc are also quite suitable. Just remember the 'well rotted' rule. Due to the relatively slow release of nutrients from manures into the soil, they tend to keep the soils at healthy nutrient levels throughout the season. One application of rotted manure after harvesting and pruning is generally enough to get the tree through until the following winter. Spread the manure 1 inch deep over the total under-canopy area (ie. The area in shade if the sun is directly above the tree). Leave about 6 inches clear around the trunk to remove any chance of burning the tree. If you choose, the manure can be spread out as far as 1 ft past the canopy as olive roots do extend further than the canopy.
Chemical fertilizers are often applied in a liquid state for ease of application and speed of infiltration into the soil. Remember, chemical fertilizers can be utilized efficiently in an olive orchard but they must be carefully monitored to avoid excessive applications. Chemical fertilizers are generally less expensive and easier to apply than manures.
There have been numerous accounts of growers overfertilizing their olive orchard by using the same quantities and strengths of chemical fertilizers as they put on their citrus or stonefruit orchards. Remember, olives are native trees.
One detrimental effect of over fertilizing is that it can lead to excessive foliage growth which requires heavy, time-consuming (read expensive) pruning to bring the tree back into balanced production. This 'growth effect' is something that can be read about in books but is most easily learned through experimentation in your own orchard.
Details on the diagnosing and correcting of specific nutrient problems can be found in the Californian Olive Production Manual. (This can be purchased from Amazon.com, see our books page).