Naturally Fruity: Avocados

Avocado
Persea americana

The avocado fruit has a completely unique taste and can take over 12 months to mature on the tree.

Growing requirements

  • Avocados are a large, subtropical tree which can grow up to 20m tall.
  • They are grown commercially in Bay of Plenty, Gisborne and Northland but are tolerant of most soils and hardy once established.
  • Avocados are frost tender. It is possible to get them established in areas with mild frosts ( in micro-climates and with protection when young) but spring weather must stay above 11oC and give several periods above 17oC to set a reasonable crop.
  • Trees are susceptible to bi-ennial bearing – a lot of fruit one year, few the following.
  • They like shelter from wind, but need full sun and adequate moisture to fruit.
  • Will withstand some salt.

Pollination

  • Avocado varieties are classified as either ‘Type A’ or ‘Type B’ and growing one of each improves fertilisation.
  • Each avocado flower opens twice. Type A flowers open as female in the morning and reopens the following afternoon as male. Type B is the reverse, it opens in the afternoon as a female, and reopens as male the following morning.
  • Pollination is by bees and insects and though a mature avocado can have millions of flowers, less that 1% will set fruit.

Choosing the right variety for you

  • The main commercial varieties in NZ are the black, dimpled Hass (A) and the smooth green Reed (B).
  • Fuerte (B) is a high-quality, thin-skinned fruit on a slightly smaller but spreading tree.
  • Bacon (B) is propagated for a polliniser and is one of the more cold-tolerant varieties – however, the flavour is rather insipid.
  • Avocado seeds are fun projects to sprout in a jar. Originally thought to be worthless, seeds from current commercial varieties are considered to have a 50% chance of bearing fruit - but it is nature’s lotto as to the quality of the fruit.

Planting

  • Avocados tolerate a wide range but prefer soils high in organic matter. They do not tolerate poorly drained, wet soils as they are susceptible to root rot (Phytophthora).
  • They are very sensitive to root disturbance when transplanting.
  • Direct-planted seeds put out a tap root and can therefore withstand more wind.

Feeding

  • Most avocados feeder roots are within 100mm of the surface and have a relatively low requirement for nutrients. They benefit from a deep organic mulch to retain moisture and insulate roots, see our guide on fertilising the home orchard.
  • Boron and zinc are the elements most likely to be deficient in NZ. Zinc deficiency shows with small, mottled leaves.
  • Magnesium and especially calcium help suppress the activity of phytophthora.
  • Excessive nitrogen causes more vegetative growth which is at the expense of fruit set and quality.

Pruning

  • Avocados need little pruning, but can grow to huge trees and since the fruit needs to be picked, being able to reach the fruit is an issue.
    Fruit is formed on the end of a branch, so thinning out whole branches is preferable to heading back the tips.
  • It is possible to have a productive tree at low height with regular, hard pruning.
  • Another method is to train young trees to five main branches. When the tree is fruiting at reasonable picking height, prune the biggest branch back hard each year.
  • Mature trees that you want to reduce should also be bought down gradually. Remove one branch per year, no more then 1/5th of the tree.
  • Prune in spring so re-growth is hardened by winter and fruiting buds mature by the following spring.
  • Nip back the tips of water shoots (fast-growing lanky regrowth) to keep regrowth compact.
  • If pruning opens up a shaded area to strong sunlight, the tree can duffer from sunburn. Spray area with diluted white paint to reflect the light and protect the tree.

Disease

  • Never hard prune a sick avocado tree. Regrowth will stress the tree even more and deplete the roots of stored energy.
  • Phytophthora is the major disease of avocadoes. See our guide.
  • Remove dead twigs, dried leaves and mummified fruit immediately as these are symptoms of ripe rots. Disinfect tools between cuts.

Harvesting

  • Fruit take 10-18 months to mature but do not ripen on the tree. A more yellow stem, and change to a duller shade of green or purple (depending on variety) indicate full maturity. Mature fruit can hang on the tree for two months.
  • Cut fruit off the tree, retaining a short stem (this prevents mould entering the fruit).
  • Extendable pole pickers are helpful to reach high fruit.
  • Ripen fruit at room temperature until the stem snaps off easily from the fruit. (Placing the avocado in a paper bag with kiwifruit or banana, which releases ethylene, will hasten ripening). Once ripe, refrigerate until use.
  • Cukes or kukes are seedless (unpollinated), small, bullet-shaped, and very edible fruit.

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