avocado

The avocado takes pride of place at the 21st century dining table – receiving honourable mentions for adaptability (adored by vegetarians, vegans and omnivores alike; as at home in savoury dishes as it is in sweet) and its nutritional profile (containing an impressive bundle of 19 phytonutrients and vitamins, including healthy fats). What’s not to like? I’ve had a few discussions lately with friends and family about exactly when some of the more unusual fruits and vegetables became part of our everyday Kiwi diets. Funnily enough, the first vegetable to be discussed was actually broccoli – it seems odd, but we couldn’t pin down when this green staple became commonplace on our plates. Peas, carrots and cauliflower seem to have been around forever, but we couldn’t remember when broccoli made an entrance. Avocados fall into a similar category, and I don’t think I would have eaten many prior to going to university.

New Zealand’s avocado industry can be traced back to the 1920s, when the then Department of Agriculture imported avocado seed, which was passed on to growers around the country. Charles Grey of Gisborne grew three large trees from this seed on his Ormond property, which began to produce fruit around 1932. By 1938-39 he was selling the fruit in Auckland as the ‘Ormond’ variety. Charles’ son Len imported new varieties into the country in 1940, among them cultivars still common today, such as Fuerte, Reed, Mexicola, Zutano and the now commercially-dominant Hass, and remained the only commercial avocado grower in New Zealand until 1970. Len’s son David has continued the tradition and is currently breeding new avocado varieties with characteristics superior to Hass.

It appears consumers took some convincing in the early days – one of the first steps Len Grey and his wife took when marketing avocados to the Auckland public in 1972 was to disestablish the link between the fruit and its now-archaic name of ‘avocado pear’ (a reference to the fruit’s shape). Len Grey’s fear was that people would think of actual pears and try to consume avocados rock hard. Thankfully, living in this enlightened age we all know better! If you wish to bypass the supermarket and have a hankering for your own personal avocado supply, with enough space in your garden and an amenable climate, such a feat is not beyond your grasp.

Avocados: a short family history

Avocados (Persea americana) belong to the Lauraceae or laurel family, along with a few familiar productive species such as cinnamon, bay laurel (think bay leaves) and camphor. Avocados are evergreen, a forest species and naturally form large to very large trees (up to about 15-20 metres in height), hence the need for space if you wish to grow one. The fruit is botanically a berry, albeit a large one, with a correspondingly large seed and thick, pimply skin. Selection by humans has favoured larger fruit with thinner skins and smaller seeds. Avocado trees are native to central-southern Mexico (more specifically the Tehuacàn Valley), and prior to the arrival of Europeans, were being cultivated from the Rio Grande to central Peru. The fossil record suggests avocado relatives were originally quite widespread millions of years ago and likely co-evolved with and were dispersed by the megafauna of the Pleistocene era (e.g. giant ground sloths). There is evidence to suggest the fruit has been domesticated in three locales, defined by three distinct landraces: Mexican, Guatemalan and West Indian, which eventually intermingled via the movement of humans. The earliest evidence of avocado consumption is an avocado pit found in the Coxcatlan Cave in the State of Puebla, Mexico, dating from 9,000 to 10,000 years ago.

The name avocado is derived from the Spanish aguacate, which is in turn derived from the Nahuatl Mexican word āhuacatl. The English name avocado is from an interpretation of the Spanish aguacate as avogato, with the earliest written English record of the word avocado being from 1696. The term avocado pear was commonly applied in England in the 1960s when the fruit first appeared on the market. Avocados made their way to Spain in 1601, mainland USA in 1825 (moving to Hawaii and Florida in 1883 and California in 1856) and South Africa and Australia in the late 1800s. Prior to 1915 the fruit was known as ahuacate in California and alligator pear in Florida (the latter perhaps a reference to the avocado’s skin resembling that of the state’s prevalent reptilian population). The Californian Avocado Association adopted the term avocado in 1915 and the rest, they say, is history. Modern global production is led by Mexico, which produces 30% (2.4 million tonnes) of the worldwide table avocado crop. At present, New Zealand produces 2% of the global avocado supply, with 4,000 hectares under cultivation, but is in fact the ninth largest avocado exporter internationally.

Suitable climates and growing conditions

The majority of New Zealand’s commercial avocado plantings are in Northland and the Bay of Plenty, though cultivation is possible in areas further south, with the prevalence of hard frosts being the main limiting factor. Trees crop well in Nelson/Tasman and I know of successful plantings as far south as Kaikōura on the South Island’s east coast. The trees are subtropical, therefore frost-tender, are susceptible to wind damage and also sensitive to sun damage, especially when young. Each of the three landraces has a slightly different level of cold-tolerance: Mexican varieties are the hardiest, surviving to -6°C, Guatemalan types moderately hardy, tolerating short periods at temperatures down to -3°C and the West Indian varieties are most frost-tender, showing signs of damage at anything below -1.2°C. A location with an average minimum summer temperature not below 14°C is necessary, as are daytime temperatures above 15-17°C and above 11°C at night for several consecutive days at flowering. In cooler climates, you could try a dwarf avocado in a pot and shift it indoors when temperatures drop.

Avocados flower over a five to eight week period in spring to early summer (roughly September to December) but this period can vary from year to year with the climatic conditions – nothing is constant with this crop! All avocado cultivars are self-fertile, but will crop better if cross-pollinated by a neighbour. The flowers are bisexual (containing both male and female parts, but express dichogamy, which is where the male and female organs are active at different times of the day. Avocado cultivars are divided into two categories (A and B), depending on their flowering type. A type flowers are female (receptive to pollen) in the morning and male (shedding pollen) in the afternoon. B type flowers behave in the reverse fashion: are male (shedding pollen) in the morning and female (receptive to pollen) in the afternoon. Therefore, for optimum cross-pollination, it is desirable to plant an A-type cultivar and a B-type cultivar. Pollination is via insects, mainly bees and flies. Avocado fruit take 10-12 months to mature on the tree, with harvest occurring from June to March, depending on the cultivar, with the final stage of ripening completed once the fruit is off the tree – there is a ripening inhibitor present in the fruit stem which prevents this final stage from happening on the tree. Fruit shininess is an indicator of ripeness – avocados will lose their shine and become dull when ready to pick. Small, long, thin seedless (parthenocarpic) fruit are quite common, and although not really commercially viable, they are known as ‘cukes’ or cocktail avocados due to the fact they resemble cucumbers and are somewhat of a novelty for consumers. They are usually a result of fluctuating temperatures at flowering.

Grafted avocado trees can produce fruit within three to five years of planting and are advised for a reliable crop within a reasonable timeframe. Although many of us remember patiently sprouting an avocado stone, pierced with toothpicks and suspended over a jar of water on the windowsill, seedling trees will take much longer to fruit and may bear unpalatable or inferior fruit to that of known cultivars – in short, the results may not be worth the wait (of up to ten years) for fruit. Seedlings can be useful as rootstocks for grafting however, but save yourself the windowsill science-project hassle and head to the compost bin instead – I’ve heard many reports of hardy seedlings springing forth from this warm, fertile repository! Commercially, the cultivar Zutano is used as a reliable rootstock but you may find the fruit in short supply. Grafting is carried out using soft, fresh growth as scionwood; cleft, side or whip-grafted onto correspondingly soft rootstock tissue in spring or early summer (usually the first few weeks of September or again in late December, when sap flow is strong). Sterile conditions are essential and the graft should be enclosed in a plastic bag until there is obvious bud movement. Avocados are difficult to strike from cuttings but propagation by air layering is also possible.

Site selection and planting

Avocados thrive in full sun, but can tolerate partial shade. Shelter from New Zealand’s cold southerly winds is essential! Wind damage can lead to broken branches as well as reduced fruit set and therefore yield. Given that avocados are a forest species, little to no wind movement around the tree is ideal. A high-sided frame built around young trees, enclosing them in shadecloth on all sides with a layer of frost cloth over the top is helpful in the establishment phase. Avocado trees are fairly hardy once mature. There is a degree of salt tolerance, but provide adequate shelter in coastal locations as too much salt spray can burn the leaves. Allow a spacing of 5 m x 5 m between trees - given the size they can reach and the fact they are originally a forest species, they can cope happily with eventual canopy closure, ultimately forming a self-mulching natural ecosystem.

Deep, free-draining soil types are required for healthy avocados, so heavy clays are best avoided – the trees are highly susceptible to Phytophthora root rots. To check whether your soil type is suitable, dig a hole and pour in a bucket of water – leave to drain. If all the water is gone from the hole within an hour, it should be safe to plant your avocado. Steer clear of waterlogged areas completely, or plant on a mound - avocado trees are not cheap to buy and they are known as ‘the princesses of the plant world’ for a reason! A sloping site may also assist with drainage. Sandy soil types are OK, but you will need to be proactive about irrigation. Avocados cannot be moved after planting, so choose your site with care – the roots of young trees are slow to develop and easily damaged. Once established, the trees have a moderate-size taproot with a larger network of shallower spreading roots, which can become invasive, so keep clear of buildings and other trees.

Mark out a circle two metres in diameter and remove all the turf. Dig a large, deep hole to accommodate the tree’s root ball with room to spare and add compost and/or rotted manure. Once you have filled in the hole with soil, water in well and add mulch, mulch and more mulch – wood chips, seaweed, sawdust and manure are all suitable, but keep clear of the trunk to avoid collar rots. This mulch will provide nutrients and aid water retention.

Culture and care

Avocados are thirsty trees – depending on where in the world they are grown, it takes an average of 70 litres of applied water (excluding rainfall and natural soil moisture) to produce one avocado fruit. Commercial plantings consequently put a huge strain on available water resources worldwide, often resulting in water shortages and even water disputes and conflict in some areas. In the summer in New Zealand, it is advisable to water each tree individually at night. Mexican varieties are better suited to drier areas and West Indian cultivars tolerate warmer, more humid conditions during flowering and fruit set. Ensure all irrigation is directed at the base of the tree.

Young avocado trees are gross feeders, and while you can apply solely organic fertilisers (rotted manure, compost etc.) they respond well to nitrogen fertilisers. Give young trees four applications annually and mature trees one application at fruit set in spring. Try Tui Citrus & Fruit Mix or Nitrophoska Extra, apply according to label directions and water in well. Too much fertiliser encourages excess vegetative growth – you won’t get much fruit and the tree’s growth can be thrown out of balance as a result.

Pruning

Avocado pruning is something of a minefield, as fruit is borne on the tips of the new growth and there is often a constant supply of fruit and/or flowers present on the trees. They can also be very fast-growing – a few metres per year, so choosing a time to prune can be difficult. Some suggestions include just after picking the current season’s crop in winter, or immediately after fruit set. Some pruning is advisable, as avocados are notoriously prone to biennial bearing and some judicious pruning may help alleviate this.

If your young tree develops a single stem, you can head this back to encourage it to bush out. Otherwise aim to remove only dead, diseased or damaged branches and cut back vigorous growth to keep the height of the tree manageable. Excessive pruning can result in sunburn and branch dieback.

Pests, diseases and what to do about them

The main disease affecting avocados is caused by the soil borne water-mould Phytophthora cinnamomi, which causes root rots and dieback. It is surprisingly common and the number one cause of avocado tree death. Your best defence against this pathogen is appropriate site selection as it thrives in heavy, waterlogged soils and can also be exacerbated by overwatering. A warning sign is yellowing of the leaves and generally droopy foliage. A resistant rootstock, ‘Duke’, is available.

In terms of insect pests, thrips, leafroller caterpillars, mites, scale insects and mealybugs can all be detrimental. Yates Success Ultra, an insecticide containing spinetoram, a soil bacterium, may be beneficial. Apply according to label directions and observe the withholding period prior to fruit consumption. Snails venturing into the canopy can also cause damage to the leaves, you may need to venture out at night with a torch to manually dispatch these however!

Varieties: My top picks

Hass – the most common commercial avocado worldwide, from a seedling raised by mailman Rudolph Hass of California – he patented the variety in 1935 and the mother tree died in 2002 (cause of death: root rot, probably good old Phytophthora). Medium-size fruit, excellent flavour, ripens in spring, black when ripe. Holds on tree over summer. A type, Guatemalan x Mexican.

Reed – large, cannonball-shaped fruit, smooth skin, green when ripe, nutty flavour. Ripens late summer-autumn and holds on tree through winter. Salt-tolerant. A type, Guatemalan.

Fuerte – large pear-shaped fruit, excellent flesh quality, ripens early winter-spring, good-doer but requires a polliniser companion. B type, Guatemalan x Mexican.

Bacon – oval-shaped fruit, smooth, thin, dark green skin, pale yellow-green fruit that is less oily than Hass but still well-flavoured. Large stone. B type, Guatemalan x Mexican.

What to do with your crop

Long gone are the days when the sole use for avocados was the ubiquitous bowl of guacamole served with every (vaguely) Tex-Mex meal on every table in every town. They are now a key ingredient in a wide array of both sweet and savoury dishes, from mousses, smoothies and ice creams to last-minute additions for hot, savoury dishes from risottos to omelettes (I was interested to learn recently that the flesh turns bitter on heating, due to its tannin content, so prolonged cooking is best avoided). In some countries avocados are more commonly eaten in dessert-type dishes, e.g. fruit salads, or sweetened mixtures flavoured with other fruits or coffee.

While you are unlikely to produce it on a home scale, cold-pressed avocado oil has gained popularity in recent years. Available in plain or flavoured varieties, the bright green oil has a subtle flavour and a very high smoke point (255°C) which renders it suitable for a range of culinary uses.

Harvested, unripened avocados store well in the refrigerator and tend to slowly ripen of their own accord over a period of two to three weeks. Take a few out as you need them and finish the ripening process in your fruit bowl – they are ready when uniformly soft and the stem stub pops out easily when you press it with your finger. I’ve also heard recently you can ripen the fruit at room temperature first, then pop it in the fridge, where it will hold until you’re ready to eat it – but I haven’t personally tested this method yet. If you have a glut of ripe avocados, they freeze well for later use in dips etc. Mash well with some lemon or lime juice (about a tablespoon for each avocado) and pack into plastic tubs or bags prior to freezing. Unripe avocado flesh is toxic and shouldn’t be consumed, and never feed any avocado flesh to birds as it can be fatal for our feathered friends.

For recipes, you can’t go past the excellent collection curated by the New Zealand Avocado group: https://www.nzavocado.co.nz/recipes/


Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/

Image credits
Avocado halves – Juraj Varga, via Pixabay
Avocado fruit and foliage – Alice_Alphabet, via Pixabay
Avocado fruit and flowers – David Lopez, via Pixabay