OLIVE GROVE PLANTING & MAINTENANCE
THE BASICS The olive will live and produce fruit for well over a thousand years. In fact there are olive trees in Jerusalem's Garden of Gethsemane that are thought to be up to three thousand years old. Olives are easy to grow. They are very hardy, fast-growing and adaptable, thriving on any well-drained soil. They do best however on deep sandy loams.
SITES: North-facing slopes are best. Shading of trees by shelter or buildings must be avoided otherwise flowering will be inhibited. Although olive trees are hardier than almost any other fruit trees, damage to young growth will occur in very exposed sites, particularly when exposed to salt spray.
SOILS: Olives do not like wet feet, therefore good drainage is essential. They prefer a soil pH of about 6 or 7. .Most Northland soils benefit from generous applications of lime. The secret to success with olives is crumbly, loose soil. In fact the ideal soil for olives, as for most fruit trees, would be the consistency of vegetable garden soil! Something to keep in mind.
Olives in Northland are growing well in all sorts of soils from sand to clay loams. Clay is fine as long as it is well drained and loosened. Gypsum added to clay improves its friability. Olives will grow and fruit on poorer, shallower or more gravelly soils than most orchard species. Very fertile soils tend to encourage excessive vegetative growth at the expense of fruiting.
CLIMATE: Olive trees prefer cool Winters and hot Summers. They are frost-hardy once established but succulent new growth can be damaged by hard frost in the first few years. Northland's high humidity can sometimes cause fungal problems. Free air movement through the grove will help reduce humidity, so wind-breaks are not always appropriate for olive trees.
SPACINGS: Spacing between rows is probably optimal at six to eight metres and at about six metres within the row, but each grower must make the decision based on variety, how trees will be pruned and whether tractor access is required. At a spacing of 6m by 6m, about 250 trees per hectare(100 per acre) can be accommodated.
YOUNG TREE MANAGEMENT: Unlike most fruit trees, olives tend to grow nearly all the time in Northland, though slowly in Winter. In order that growth is not checked, young trees need adequate water in dry periods. Before young trees are planted its important that the roots are moist and the ground is also moist and friable. Young trees growth will be reduced if they have to compete with long grass or weeds. Little pruning should be done for the first two years or so (until the tree is about 2m to 2.5m tall) unless some major correction to the tree's shape is necessary.
IRRIGATION: The installation of irrigation allows planting to take place at any time of year without the young tree's growth being checked. By maintaining optimum growth throughout the year, the trees will reach a productive size sooner.
Over-use of irrigation, particularly in heavier soils can cause serious root damage or death.
MULCHING: Mulching in early Summer will help retain soil moisture and control weeds. Mulch may need to be removed during wet Winter months to allow maximum evaporation.
FERTILISERS: An initial soil test to establish pH and macronutrient levels, followed by annual leaf tests, will assist in application of optimum quantities of the right fertilisers. There will also be a cost saving by eliminating wasteful usage. (I suggest sending small samples from soil surface down to 150mm depth to R. J. Hill Laboratories, Clyde St, Hamilton. The results can then be taken to Veg-Gro Supplies Ltd in Porowini Avenue, Whangarei where your fertiliser requirements can be worked out. In sending off the soil samples, ask the lab to do general analysis plus a reading for Nitrogen content and Boron content.)
Fruit is borne on the previous Summer's growth, but there is a tendency for Northland olive trees to be over vigorous at the expense of flowering. Although olives need soil nitrogen, some restriction on its use may encourage better production. Adequate amounts of potassium and phosphate are needed to encourage flowering and fruiting.
Most NZ soils are deficient in zinc and boron which can be supplied by an annual foliar spray of zinc chelate and "Solubor".
PRUNING: The pruning of olives is the source of much discussion, but it seems that in windy and/or sloping sites the main objective is to keep the trees low and broad for stability and ease of picking. Usually a broad vase shape with three or four main leaders is best.
Trees should be kept open to allow good light penetration. Height should be restricted to about 3 metres to facilitate picking without ladders. Recent evidence also suggests that the lower the tree the heavier the crop. Single leader or mono-conical pruning is used to enable machine harvesting of some varieties.
BIENNIAL BEARING: Olives characteristically tend to bear heavy and light crops in alternate years. This can be minimised by pruning off a proportion of the fruiting wood after a light crop(May) or soon after fruit-set of a heavy crop (December). Also fertiliser should be increased when trees bear a heavy crop and reduced when a crop is light.
DISEASES: The most prevalent disease of olives in NZ is Peacock Spot, a fungal disease affecting leaves and fruit. This can be controlled by one or two applications of copper spray such as Kocide or Oleo 40 (talk to Veg-Gro Supplies) post harvest and/or in the Spring. Copper should not be applied to trees bearing fruit as oil quality could be affected.
In very wet conditions Phytophthora, a pathogenic fungas, may attack roots. This can be serious but foliar sprays of Foli-R-Fos can prevent it and will also aid recovery from the disease.
"Olive Tip Die-back" is another problem with some varieties. It is caused by a native weevil that invades the soft growing tips and causes distortion and death of young shoots. It is easily controlled by spraying with insecticide such as "Confidor" in Spring and Summer.
PESTS: Leaf Roller and cicada damage are generally superficial except in the first year or two, when it is recommended that cicada damage be pruned out at the end of Autumn.
Birds eat olives when they are ripening. Generally for pickling and for oil production, they can be picked when green-ripe, or just as the olives begin to change colour, before the birds get too interested. Riper olives make mellower tasting oils, so bird scarers or netting may be an option to overcome this problem.
Rabbits can do serious damage to the bark of olives, so they must be protected from rabbits from day one. Plastic spray-guards are effective and cheap (Veg-Gro Supplies).
Applying a mix of acrylic paint and egg to the trunks also repels rabbits.
Possums do not harm olives.
It is not advisable to graze stock among young trees as they will eat the leaves and bark. High pruning of the trunk and protective elastic webbing around it will allow light grazing by sheep after about five years. This does however equate to a loss of production from the skirt of the tree.
POLLINATION: Olives are mainly wind pollinated so should be pruned to allow wind movement through the trees. There is controversy over the role of bees in pollinating olives, but as large numbers of bees are seen working the flowers, the inclusion of beehives in the grove seems desirable.
Although some cultivars are self-fertile, others are only partially or not at all. It is sound practice to plant several cultivars together to ensure that cross-pollination takes place.
Leccino needs a pollinator and traditionally in Tuscany that is Pendolino, but it seems that Koroneiki and J5 (and probably others)also pollinate Leccino.
HARVESTING: Fruit intended for pickling needs to be hand-picked to avoid bruising. There are various means of harvesting oil olives including hand-stripping, pneumatic vibrating fingers, olive rakes and mechanical tree-shakers. The strength of attachment of fruit differs greatly between varieties and will influence how the fruit is harvested.
The cost of harvesting will be the major on-going expense in olive grove management.
Oil olives ideally need to be processed within 24 hours of picking. There are a number of press owners around Northland who will press your crop as long as you have booked well in advance and negotiated the terms of the pressing arrangement (money per kilo or a percentage of the oil).
I strongly advise any prospective olive grower to join the Northland Olive Growing group, "Oliveti" by phoning Maxi Thompson at 09-4362365. The group is an invaluable source of information, workshops and inspiration that will save you a great deal of frustration and many mistakes..
Important reading on the subject: Gareth Renowden's recent NZ olive book, available from Touchwood books or The Albany Olive Press.