Growing Olive trees
The olive tree is evergreen and known for its longevity among other trees - it may live for up to 2000 years!
Olive trees will tolerate a large range of soil conditions, preferring a neutral to alkaline soil type. Olives will often grow in hilly, rocky areas that are not suitable for other crops. However, they do not like very heavy soils that hold excessive water after wet periods.
It is important to understand your soil type, structure and pH prior to planting. After the trees are in the ground, there is very little you can do to alter drainage and other essential factors. You can buy a very easy-to-use pH Test Kit from Olive Agencies to do your basic tests.
Olive trees like cool/cold winters and hot summers. Even though olives are evergreen trees, they still need a cool winter so they can rest to prepare for their main shooting, flowering and fruiting in the spring.
Throughout the world olives are grown in climates which range from the cold of Tuscany (Italy) where -20°C is not unheard of, through to warmer areas such as Seville (Spain) where some regions don’t even reach 0°C during winter. Summer temperatures are important for the growth of fruit-bearing foliage. Most olive growing regions of the world have average maximum daily temperatures, in the hottest month of summer, somewhere above 30°C. Afternoon temperatures as high as 45°C have very little effect on mature olives as they have an inbuilt mechanism which temporarily shuts down their system until the cooler part of the day arrives. However, apart from the cool winter and warm summer requirements, the moisture levels of the tree must also be adequate.
Keep a good eye on the health and moisture levels of your trees during winter to ensure that no damage occurs.
The main factor affecting the spacing decision is the type of harvesting machinery to be used on the grove. Harvesters are manufactured for all densities but their availability to your grove’s location must be considered.
Mainly use machine picking when you only produce olive oil, but when producing table olives, one has to
go back to traditional way of picking.
There is ongoing research in every olive growing country to ascertain the best tree spacing for mechanically harvested olive groves. While there has been a tendency towards closer spacing in the last decade, harvesting economics on densities closer than 400 trees per hectare are still being assessed.
When to Plant
It is widely accepted that olive trees can be planted in irrigated olive groves year round if the winter temperatures do not fall below -5°C. Traditional plantings in Mediterranean countries are done in the autumn leading up to the winter rains. However, access to irrigation water reduces the need for such seasonal planting. A properly irrigated grove will withstand much greater extremes in temperatures than a traditionally planted dry land grove.
Planting an Olive Tree
Just like any tree, there’s more than one way to plant an olive –
If your soil requires the addition of lime to bring it’s pH level to 7.0-8.0 (neutral to alkaline), then add the required amount to the manure and crusher dust above. Contact your local Department of Agriculture or fertilizer company if you need pH testing done and lime quantities worked out. Many growers use a spreading contractor to apply the lime along the total row rather than just at each individual tree site. Your own inexpensive pH test kit will be handy for spot checks throughout the grove. More details on the use of lime for olive tree health can be found in OLIFAX 15.
Next, deep rip at least 10 to 12 furrows along the full length of the planting row to a depth of 600mm or more and a width of at least 3m. The nutrients will be suitably mixed in as they drop down the ripper grooves.
This preparation will give the roots an excellent start and fast growth will result. Wide shoed rippers pulled by a good sized dozer will do an excellent job. You may wish to finally level the ripped area with offset discs,
a rotary hoe, blade or similar.
In poorly internally drained soils, deep ripping both along the rows and then some cross-ripping will increase subsurface drainage. Please consider possible erosion when planning the direction and timing of your ripping. Deep ripping during a heavy rain season may result in erosion if grass cover cannot be quickly re-established.
After selecting the tree site, positioning your stake, and wetting the planting site, plant the tree at the same depth or just slightly deeper than it was in the pot.
Do not tease the roots out before planting as this will stress the tree by damaging the young brittle roots.
Press soil down lightly around the tree roots to remove any air pockets and make a slight depression to act as a watering basin.
Water thoroughly immediately after planting and mulch with coarse straw to conserve water, cool the soil, and reduce weed growth. The best mulches to use are those that contain plenty of nitrogen and other minerals to feed the tree. These include lucerne, soya bean and pea hay. As the mulch decomposes over a period of time, the nutrients are transferred into the soil by earthworms, rain and micro-organisms. If using mulch, try to buy spoilt (rain damaged) bales. Loosen up the ‘biscuits’ before applying.
Hammer milled pine wood waste can also be used but an occasional nitrogen fertiliser application will be needed to reduce its leaching effect. Carefully used, well rotted manures can also produce an excellent mulch.
If you are in an area with long, cool, wet winters then mulch may hold too much water during this period. Remember to keep your mulch about 100mm away from the trunk to allow the tree to breathe and to avoid contact between the trunk and wet mulch.
Continue your irrigation according to the section on “Irrigation” and using general common sense.
Be careful not to waterlog the soil as excess water is the olive’s worst enemy.
NB. All trees are ‘container grown’ and can be planted in moderate climates (eg. winters that don’t go below -5°C) at any time of the year. Very young trees may need some protection from severe frost and animals.
No transplanting shock will occur if the simple instructions above are followed.
Growing, Pruning, Fertilizing & Watering
The staking of young olive trees is very important. Stakes need to be strong enough to support the tree while the anchor roots are developing, and yet flexible enough to allow the tree to move freely in the wind.
If the stakes are too rigid then the tree will be over supported and not sense the need to develop strong roots and a thick trunk.
Our commercial grove sized trees are only lightly staked and will need to be tied to a heavier stake at or soon after planting out. The trained straight trunk will make fruit harvesting easier if a ‘tree shaker’ is to be used. The final stake should be 1500mm long and
16-20mm thick. Two types of stakes – coated steel and bamboo – are available from Olive Agencies.
Steel stakes are coated in a hardened, waterproof and UV stabilised polyethylene and, like bamboo, are smooth, light and flexible. Because of their durability, they will last many years and can be used a number of times.
Trellising is more expensive than the common bamboo stakes used on traditionally pruned groves but is necessary for the development of monoconical groves. Trellises are also used in groves with densities greater than 400-500 trees per hectare as monoconical pruning is considered the only viable method for such intensities.
Olive trees need very little water to survive if serving as an ornamental or landscape tree. However, for a good crop, mature olives generally need at least two waterings to field capacity (full depth of roots – approximately 1m in mature trees), each winter (this will depend on your soil type). If more is available during winter and at other times of the year then this will be most beneficial and will result in increased crops.
In fact, it is generally accepted that a drastic reduction in rainfall and irrigation water will result in a poor crop of only one third to one half of a fully irrigated commercial crop.
It must be remembered however, that the olive’s worst enemy is too much water – especially during the winter months when there is less evaporation taking place.
So keep a good eye on the moisture levels in the soil around your trees. Winter watering keeps the trees healthy for a good spring flowering and a good fruit set. When the fruit has set, in addition to natural rainfall, supplementary watering is needed to achieve a good fruit size and high oil yield per hectare.
Every tree likes good quality water but the olive tree is still one of the few fruit bearing trees that will survive and still bear quite well with poor quality saline (salty) water. Saline water that is unfit for human use is generally quite suitable for olives. Olive trees grow and crop well using water with a conductivity of up to 2,400 micro S/cm (This can be translated to Total Dissolved Ions by multiplying by 0.64. eg 2,400 mS/cm x 0.64 = 1,536 TDI). If saltier water is used, it should not be sprayed onto the leaves and the ground will need to be ‘flushed’ with good rain water from time to time.
The higher the conductivity increases above 2,400 micro S/cm, the more the olive crops will begin to decrease in tonnage.