How to grow olives

By Denise Cox 

First published in Organic NZ May/June 2017 

 Olives (Olea europea) are evergreen trees native to Northern Africa. Cultivated since prehistoric times, olives are integral to the culture, diet and economies of the Mediterranean basin. Spain produces 45% of the world’s crop. Trees dating from biblical times still grow in the Garden of Gethsemane in Jerusalem. 

Although European settlers planted specimen olive trees in New Zealand in the 1830s, commercial olive growing didn’t begin until the 1980s, when cuttings were imported into Blenheim. The first official pressing in 1991 in Marlborough yielded a single supreme litre of extra virgin olive oil, spurring a modern-day gold rush.  

Today there are over 250 olive groves, most containing 100–1000 trees. The main olive-growing regions are Northland, Auckland, Hawkes Bay, Wairarapa, Nelson and Canterbury. Most plantations are sited at altitudes up to 200 metres on flat or hilly land, receiving over 2000 hours of sunshine, and 700–1349 mm annual rainfall.  


Growing conditions  

Traditionally olive groves were planted on steep rocky hillsides, with sheep and goats for company. They love poor-quality free-draining soil and a hot, sunny position, sheltered from winds. Trees are aesthetically pleasing whether planted as a single specimen, in groves, hedges, tubs, espaliered or topiarised. Add lemon, lavender and rosemary bushes to create a stylish Mediterranean-themed garden. 

Olive trees are hardy to –10ºC, but late frosts will damage blossoms. They don’t tolerate wet feet and will die; and won’t fruit well in humidity. The optimum pH is 6.5.  

Many varieties are self-fertile; others need pollinators for optimal fruit set. Trees are wind-pollinated and pollinator trees should be planted close by. A decade-old tree produces 20–40 kilos of olives, yielding approximately 150 ml of oil per kilo of pressed olives. Some cultivars are great for both oil and eating, others are best for oil.  

Plant trees in spring after frost, or in summer and autumn if they’re irrigated. Space trees 6 m apart. Fill planting holes with compost, and mulch with composted manure. Stake trees and put mesh collars around their trunks to deter predators and stock. Control weeds as trees establish, by mowing and mulching, or using geese, horses and sheep.  

Olive trees have legendary abilities to withstand drought; however, trees that are irrigated will produce sooner than those that are dry farmed. 


Harvesting and processing  

Harvest olives from late March onwards. Olives can be pickled at any stage as they change from verdant green through purple to black. Olives for oil must be fully black.  

Birds adore ripening olives: net trees, or use bird scarers if you want to keep your crop.  

Harvest olives by stretching tarpaulins under the trees. Whack the branches with a pole so that the olives fall to the ground.  

Unless you’re a bird or a possum, olives can’t be eaten straight from the tree, and must be processed to make edible table olives. Olives swiftly deteriorate from the moment they fall from the tree, so must be pressed within 24 hours. Those left for longer will produce inferior fusty oil.

Denise Cox is a writer living on an organic block in Kerikeri. She was a commercial organic grower for two decades.


Tips and facts
 

  • Select olive varieties that are proven performers in your area, grown from local rootstock. 
  • If planting a single specimen, choose one that is self-fertile 
  • Frantoio, Leccino and Barnea are the most commonly planted varieties.  
  • Pollinators will improve crop yield. 
  • Control weeds. 
  • Fertilise sparingly.
  • 90% of olives are pressed for oil, 10% are processed for table olives.
  • It takes 5–10 kilos of fresh olives to make a litre of extra virgin olive oil. Lower quality oil is extracted from the residue. 
  • Agree processing times and quantities in advance if contract-pressing your olives. Some presses won’t accept small quantities for pressing.  
  • Use pulp for compost, animal fodder or fuel.

A boutique olive orchard 

David and Noeline Penny’s boutique olive orchard in Kerikeri contains some Leccino and Koroneki, but mainly Frantoio cultivars propagated from rootstock from olive trees grown by the early Northland missionaries. 

David Penny shows how his shaker works to harvest olives

“Olive trees dislike humidity so our trees need to be adapted to the Northland weather conditions,” explains David.

Weeds are controlled by mowing and mulching the grass and olive prunings. Trees are pruned to maintain an optimal size for picking.  

“We spray the trees with seaweed fertilisers, after picking, and during the growing season. We also use custom made supplementary feeds developed by Fodda [BioGro certified, www.tuturu.co.nz], which address nutrient imbalances identified in our annual soil tests. Seaweed is superb for maintaining the health and vigour of the trees, and helps reduce peacock spot, a fungal disease which swiftly defoliates the tree.” 

Trees started bearing when five years old and now bear several hundred kilos of olives annually. “If you press an olive when it’s ripe the oil just squirts out and we know they’re ready to pick,” says Noeline. 

A battery-powered rotary shaker shakes the olives from the trees, which are emptied into a deleafing machine that separates any leaves from the olives before pressing. 

“As small growers, it’s uneconomic to own an olive press. It’s vitally important when picking to network with a grower who will promptly press the olives, so that we get the best quality oil. Some owners of presses are selective and will only press olives that are the same variety as the ones they grow.”

Olive varieties 

Olive  Type  Use  Pollinators  Qualities 
Frantoio  Tuscan 

 

Oil, table  Self-fertile  

 

Vigorous, disease resistant. High yields. Sensitive to extremes. Best for warmer areas. 
Leccino  Tuscan  Table, oil  Pendolino Moraiolo, Frantoio  Very cold and disease-hardy. Vigorous. Early prolific cropper.  

Sweet medium to low acid olives. 

Barnea  Israeli  Oil, table  Picholene Picual, Manzanillo  Vigorous growth; needs stringent pruning. Disease-resistant. Large olives. Prolific producer in ideal conditions; hates cold winters. 
Kalamata  Greek  Renowned table olive; oil 

 

Manzanillo, Koroneiki  Vigorous erect growth. Hates extremes. 
Koroneiki  Greek  Oil  Self-fertile  Vigorous, disease-resistant. Prolific cropper. Small olives. Ideal for coastal areas, hedges, screens and containers. Low chill requirement: suitable for warmer areas. 

Picual  

 

Spanish  Oil, table  Self-fertile  Bears early. Highly productive compact tree. Dislikes humidity.  

Picholine 

France  Gourmet table, often pickled green, oil  Leccino and Manzanilla  Upright. Cold-tolerant, adaptable, disease-resistant. Excellent pollinator. 

Photos: Denise Cox