How to grow olive trees, concise and complete guide
When planting olive trees, it is advised to place a bed of stones to allow water drainage, this is not necessary in warmer climates, and possibly counter productive since it will hinder jobs of wood chirurgy when the trees grow older.
A stick is used to force the tree to grow vertically in its initial stages, the stick should be places in the opposite direction of the strongest wind of the zone, to counter-act the constant bending process applied by the winds the main trunk.
There shouldn't be done any pruning, and let the plan grow in his natural bush shape.
Roots at the younger stage grow as taproots, deep in the ground and short on the sides. This is mostly an effect caused by the early shaping given to the plants grown in the plant nursery. Plants sprouted on the wild should start to grow adventitious roots right away. Taproots are bad because after the younger stage, after adventitious roots eventually take over, they start to rot, leaving the plant vulnerable to underground fungi attacks.
Younger plants are more vulnerable to drought.
It is the time to choose the main branches that will split the trunk in 2 and then 4 derivations.
Make sure the chosen branches chase outward and each at different corners of the square of the section.
The first split should be around 80cm-1m from the ground.
Their inclinations should be 30/60°.
Make sure that the chosen branches are not fully pendulous and have smaller branches chasing upwards.
The one just described is the most common pruning method for olive trees in non superintensive plantations. Other methods like epsylon and christmap tree haven't shown advantages so have fallen out of favor.
The only valid alternative to the polyconic shape is the globe shape, although the polyconic shape can be tweaked to satisfy the properties of the globe shape by growing a thin dome of small branches stemming inward from the tip of the highest branches.
This is the time around trees start to consistently yield good harvests. Pruning at this stage consists of
cut away the exhausted branches, which are those branches which are closer to the base of the branch connection (to the bigger branch), and that are older than the other branches (closer to the tips). Those branches (which have produced olives in the past years), overshadowed by the smaller and younger branches closer to the tips, have by now reduced flow of sap and will slowly dry up as the tree is redirects the sap where the branches can metabolize more carbs thanks to higher light exposure.
cut away shoots, which are very close to the branch bifurcation; Since the place where the bifurcation happens is usually horizontal, the branches that sprout from the dorsal of the branch tend to grow out vertically in their inevitable search for light.
Don't cut all of them, start from the base and cut 2 or 3 (although it depends on the size of the branches) and leave the rest, which will become the productive part of the branch in the coming years.
cut away branches that are too long, and escape the shape of the canopy.
but also the ones that are too inwards, because you always want to shape out a production branch as a V, with the omnipresent objective of increasing airflow and light exposure.
cut away all the shoots that sprout from the main branches and grow upward or inward (toward the center), making sure to leave the ones chosen to replace the main branches themselves (which should be upward or slightly outward).
cut away as many ill branches as possible (like branches affected by the olive knot), but making sure to always leave something. Usually pruning shouldn't remove more than 1/3 of the canopy, but in extreme cases it is acceptable to reach 2/3.
by growing substitutes closer to the center of the tree stemming from the to-be-replaced branches that are:
ill, weak (low vegetation) or dry (victim of roots rotting)
too heavy (such that the inclined branch overshadows neighboring branches)
The substitutes should be tied (with a lace or equivalent) to the branch to be cut, with the goal of guiding the younger branch in the direction of the older one.
How do branches sprout younglings? The tip of each branch sprouts always two gems at a time (on opposite directions), with alternating 180° orientation at each generation. One of the branches is sterile and goes upwards, where as the fertile one tend to be pendulous. This is not an accurate definition but can help choosing which shape to give the tree. Every branch will eventually become fertile by sprouting newer branches on their tips. Sprouting happens in spring and autumn, which are usually the periods with higher humidity, and tends to align with pruning periods, which makes the choice of the time of pruning also important.
At what time of the year should tree be pruned? Olive trees slow down in winter and summer (because of drought), which makes these the ideal times for pruning. However in summer pruning branches bearing fruits is not ideal even if not damaging for the tree itself. Since plants break dormancy after ~11° The ideal time to prune (or at least make the most decisive cuts) is in late winter (such that open wounds won't be affected by harsh frosts), early spring (before the tree starts to choose how many resources to reserve for fructification).
cutting the peaks that are too high (always leave the edge) 
The maximum desired height of the tree depends on the length of the ladder you use for pruning (if you use the ladder), or the length of your telescopic tools (if you don't use the ladder.)
dig out rotten wood caused by fungi attacks at the base or on the branches with a chainsaw or an hatchet.
When you prune, any choice boils down to performing cuts, the way you make them influences the tree, and since you can average hundreds of cuts per tree, all of them stack up. These rules are applicable to any tree in general, and not just olive trees.
The bigger the cuts, the more weight these rules carry, as a rule of thumb:
less than 1cm are inconsequential
more than 2cm things start to matter
Remember that the area is a quadratic function, which means that the effects of increasing differences in the area also grow as a power of two.
How much to leave? Leaving too much results in a stump (and possibly enticing the plant to sprout more smaller branches on the stump with the goal to restore the flux of sap, which will result in the formation of annoying to prune bush-like branches), leaving to little will form holes in the bark (holes are bad, they leave the inner sap flow more exposed to externalities, and allow water to stagnate, forming an ideal habitat for antagonistic phytophagous fungi).
Since most of the cuts will involve cutting suckers, which have an age of 1-3 years (or more generally an age less than or equal to the pruning frequency), it is easier to differentiate the younger bark of the shoots, from the older one of the main branches, the cut should be performed at this boundary, such that all the young bark of the shoot is cut out, and no old bark is removed. 
If the branches are older, and the age difference of the bark is not easy to spot (at the boundary they both look old), another clue which aids the cut is the cone-like shape of the branch to be cut. Usually the boundary between the branches is not a rigid angle, instead it resembles a graceful curve. Considering the vertical section, the cut will be performed when the two parallel lines of the branch will cross inwards into the bark. 
The direction of the cut in general has to be orthogonal to the direction towards which the branch to be cut is growing. Performing cuts this way ensures that they are as small as possible because (considering the horizontal section) the cut is closer to a circle and further from an ellipse, since given the radius of a circle, and assumed that the minimum radius of the ellipse is the same as the circle, the area of the ellipse will be always above or equal to the area of the circle. All in all, it means smaller cuts lead to smaller wounds, which leads to faster healing and a lower probability of diseases. 
There is an exception though, when cuts will end up facing upwards, it is preferable to make them slightly oblique; this allows rain to slide down like it would from a roof, instead of inexorably digging holes in the wound left by the cut.
Younger branches are more fibrous, older ones are more ligneous. What this means is that left-overs from younger branches will more likely dry up. Since fibers are more porous, they are more susceptible to wind and sun compared to denser older ligneous branches. Also the thicker bark of older branches prevents humidity from escaping.
Prune one (of the 4) angle at a time, starting from the top and descending towards the base.
Unless you plan on cutting tertiary branches that have grown downwards too much, in which case you start from those, and then will proceed as normal, top to bottom (although with less intrusive cuts since you just performed a big cut at the base.) 
Olive trees need lots of nitrogen, because they have to always replace their foliage. (For a more detailed breakdown of all the minerals look at this paper)
As in most plantation you want a mix of soluble and organic (slow transfer) fertilizers
Water is important in spring, before and during flowers blossoming, to aid fructification; neglecting to do so in a dry spring, will cause most of the small fruits to fall before reaching summer.
Water is also important during summer, not for the fruit quality, but still important for the plant and the harvesting period. Since the mechanical way to harvest olives is through tree shaking, a weak tree subject to such stress will loose also too much of its foliage, therefore it is important to make sure trees have a tight canopy before the harvest. Summer irrigation also makes fruits grow rounder (and slightly bigger, although olives size is dependant on the cultivated variety)
Some people say that watering olive trees during summer leads to a higher yield of olives, but not an higher yield of olive oil and make oil extraction harder (as machines have to separate more water from the oil). In my experience this is not true.
Olives coming from trees irrigated throughout summer are first and foremost healthier. Healthy olives have an higher yield, the skin has less chance of breaking and preserves more substances inside the pulp. Both the seeds and the pulp are bigger, and since olives are not grapes [1], necessarily they will have more oil.
| [1] | Berries-like fruits are able to store higher water contents without enlarging the fruit itself, like bags. This is not true for drupes. |
The roots need oxygen, a porous soil is ideal, and allows the roots to expand without risking asphyxiation. Porous rocks mixed with the soil can be helpful to keep the soil aerated, without resorting to plowing.
Trichoderma and mycorrhizae help against wood rotting, which should be spread in the soil as close as possible to the roots. Despite these treatments having no healing properties (they are a form of prevention), they can be considered a treatment in the case of olive trees because of their perennial nature, their average strong vigor and their natural ability to marginalize phytophagous fungi. In other words, since olive trees "heal themselves", trichoderma and mycorrhizae can be considered healing boosters.
Plowing, tilling or grass? It depends on the type of soil and average weather, however:
because olive tree roots don't usually grow deeper than 1 meter, tilling is preferred to plowing. Olive trees tend to also grow on rocky soils, where not even tilling is possible, and soil operations are reduced to mowing. Plowing and tilling works better when using herbicides to control weeds growth, whereas without herbicide mowing helps to preserve the bacterial ecosystem of the soil. When choosing to mow, controlling the type of herbs left over can be beneficial, like for example opting for drought resistant grass. The main advantage of plowing/tilling is deeper oxygenation, grass on the other hand helps against soil erosion, decomposition of soil nutrients, droughts (through higher water retention). It is also common to cover the soil by an 80% with breach, in which cases only tilling is applied on top.
Olive trees are very resilient plants, but are light seekers . Overall it is easy to grow olive trees where there is a lot of sun and just enough water. The plants have natural methods to stem off diseases, and require attention against only 3 major pathologies (spots, rot and fly), while the rest can be considered minor. But it doesn't like harsh climates, it doesn't tolerate well temperatures below 0° and above 30°, too wet climates and too dry climates. Although growing olive trees is possible across a wide range of latitudes, it is only economically viable in subtropical regions.
It was thought that growing cereals among olive trees was bad because the light reflecting properties of the ears would stress out the olive trees and therefore legumes were preferred. Legumes do indeed produce more nitrogen, which olive trees crave (on average more than other plants).
