Avocados – Pears from Paradise

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Organic NZ Magazine: July/August 2001
Author: Tim Vallings

One of the most delicious and nutrient rich foods available, avocados still have an air of mystique and luxury but they’re not that hard to grow. Tim Vallings tells us how to grow the best avos, sustainably!

I’ve been asked how we grow our avocados and why I think they are the best.

We generally avoid calling our produce “Organic”, as we feel this term has problems. There are many completely “organic” (that means containing carbon) substances which are totally toxic to humans. We have devised a food-producing system for at least one crop which we believe to be the most productive and sustainable food-producing system known.

We don’t use any pesticides, insecticides or fungicides – including those that are allowed under BIO-GRO or Demeter labels – and we believe our produce is better for human health than anything presently available and production is more long term sustainable.

We call our system “Natural farming”. Top quality food can be produced commercially with a totally different, sensible sustainable system. Many of the popular horticultural practices are extraneous, impact negatively on the environment, and don’t help produce a better crop. We have high yields and really large quality fruit, which are a meal in themselves. Here’s how:

 

Mulching

We have found avocados to grow on the ground more than in it. An avocado is a plant that thrives on a really good layer of mulch. To grow avocados well, the carbon content of the soil needs to be built up. This fact is at last widely recognised in avo circles and it is gratifying to see shelterbelts being mulched (instead of going up in smoke!). But if mulching involves chipping and transporting it is extremely energy intensive and certainly not sustainable if everyone did it. You also run the risk of bringing in weeds, as well as unwanted fungi, and compacting the soil still further.

The biodynamic compost making is great but on an orchard scale ends up problematic because of the high energy consumption and time spent transporting it around the farm. It is also unsustainable when materials are sourced from another system.

It is possible to grow all the mulch you need right where you need it, just like in a forest. We cultivate various mulch plants in alternate rows next to the avocados and mulch them down periodically– whole logs, branches and all take no time to rot down in the active top soil. Chipping does not happen in nature and is not required (simple hand tools like machetes make branches easier to handle). Our orchard tends to look “a shambles” to people used to the more conventional systems – native herbs and shrubs sprout in every corner, weeds and wild vegetables rampant in places.

This healthy natural chaos of biodiversity has less insect pests and more predator insects (Dr Phillipa Stevens DSIR), than our chemical neighbours. We don’t seem to need to inject our trees as most people do to try to prevent them keeling over with the dreaded phytophthora. Injecting is a time-consuming job, popular virtually from the birth of the avocado industry locally, and all over the world these days. Avos are a risky crop, they can all drop dead on you if you don’t understand them well and supply their needs. One avo tree can have more than 100 fruit on it if all its needs are met. It is not about how many trees you have, but how many fruiting canopy hectares.

 

Air and soil

Plants grow in air not soil, they grow in the air gap between soil particles. Air is critical in soils. Soils with adequate fertility can show up symptoms of nutrient deficiency in plants if the air-filled porosity is too low. Fertiliser can solve the deficiency problem because the few living surface roots take it up, but this does not solve the real problem.

Air is often incorporated into soils manually by cultivating, but this must occur before planting and not after, otherwise sensitive avocado roots will be damaged. To maintain air-filled porosity is difficult with a perennial crop. It is necessary to avoid heavy vibrating machinery in the orchard (like tractors) as much as possible, especially when the soil is wet.

With our “row mulching” system we tractor only one side of the plants for the whole life of the tree – we never tractor in the mulch rows. We mow one side of the plants when they are young, to establish them among groundcovers and “weeds”. The mown row enables us to be able to walk around and inspect what’s going on, rectifying problems like hare damage or whatever. Later on, it enables us to move our ladders around and pick our crop efficiently.

We pile our mulch (which is often in head-high piles) around one side of the trees. We cultivate groundcovers that we consider useful or beneficial in some way and easy to mow. A variety of plants living and dying provide plenty of fodder for an ever-increasing species of beneficial soil biota. Deep roots of quick-growing plants that are the pioneers of the orchard rot just as quickly as they grow, and provide deep worm ways, waterways and airways. It’s not practical to add worms to do the job, it’s necessary first to condition the soil so that worms will thrive and multiply.

 

Fungi

So little is known about some forms of life. Upheavals in the classification of plants are common. An unknown percentage of insects remain unclassified, the clear distinction between plants and animals has had to have a radical rethink. Fungi is not a “colourless plant” (as once thought) but actually made of chitin, the same stuff of insects’ exoskeletons.

I think it absolutely wrong to introduce yet more foreign predator insects (like this new wasp for thrip control). It is a biological cure but the Royal Forest and Bird Protection Society and Department of Conservation opposed its introduction because of unknown long-term effects. We should better understand the predators we have in NZ already. The scientists are surprised that there is no thrip “problem” in our orchard. They should work out why that is before introducing a new potential problem. Haven’t we learned anything? It is similar arrogance that has led to the environmental problems caused by genetic engineering.

Various beneficial microfungi are appearing on the market and could be a better idea to solve harmful pathogen problems, rather than copper or other fungicides. Copper is used widely and considered a “soft option” spray and is permitted for organically certified orchards. Copper does work and is useful but use of copper sprays can cause it to accumulate in soils to levels as high as those found in areas where copper is mined. In fact, these levels have already been found in older plantations where copper has been overused.

In a study of Organic farms compared to conventional ones (on the exact same soil types), AgResearch scientist Dr Nick Waipara found that more species of beneficial fungi were present and in higher numbers than on conventional farms. We believe the answer is in stopping all fungicide use, providing conditions to suit and introduce local species of fungi which seem to have the ability to reduce disease (perhaps occupying the niches that pathogenic species would otherwise occupy). We have found dried commercial preparations to be largely inactive which is possibly just as well because we could be mucking it up for ourselves by trying too hard to introduce foreign species when the local strains seem better suited to NZ.

I believe a surprising number of unrelated species are in a joint venture with each other for mutual benefit: one of the most widespread of these associations is mycorrhiza – a partnership between fungi and roots. In return for a sugar supply, fungal hyphae transport minerals to the roots from far and wide (in some situations certain species of plants have no need to grow many roots at all). In nature mycorrhiza are widespread, they are the rule rather than the exception – understanding and encouraging them is critical. It is my observation that copper and other fungicides are detrimental to these beneficial associations.

Time-honoured methods can easily be 40 years or more of doing the wrong thing. For example, if CFCs had gone into mass production 50 years sooner, we would have lost the protection of the ozone layer surrounding the earth before we even knew we had it.

 

Give them room

We don’t ever irrigate our trees, believing it to be an unnecessary expense, as well as counter productive. Avocados have a tendency to get too big, so why water them only to have to cut them back? The harder you prune them, the bigger and faster they grow, and topping them can have the opposite effect to the one you want.

The only way to handle the trees is to give them plenty of room – you could easily plan on an ultimate spacing of nine per hectare on most types of plush avocado dirt. Plant too close and you will have to ruthlessly thin to allow light to get right to the skirt of the avo trees. If this does not happen, the avos will form a canopy way up high with the fruit being reached with the greatest of difficulty. Well-spaced trees are the answer. They crop heavily and bring the tops down with thousands of heavy fruit – you can reach heaps from the ground without even using a ladder or longarm.

 

Pests and predators

Leaf roller can be a real problem and is in most avocado orchards around here. Bt (Bacillus thuringiensis), a naturally occurring bacteria, is widely used by Organic and conventional growers alike. There are very few biocides of any origin that are really specific and, contrary to popular belief, Bt kills a certain number of beneficial creatures along with target ones.

We need to proceed with caution when interfering in the complicated web of interdependence in a community of species. It is so complex that we cannot predict the long-term result of blindly spraying. A clearer look at the problem is required – observation without knowing anything or expecting anything, like a child, helps me to understand what I need to do.

A balancing of the food chain needs to occur. Birds are the insects natural predator so boosting bird numbers is important, but this in itself can be difficult. Unseen predators are at the heart of this problem – rats, mice, cats, ferrets, stoats, weasels and possums. Adjusting this balance to put us back on top along with the birds is the go here.

Time normally spent on spraying should be put into pest control and nurturing native fauna. We have devised many cunning and cheap ways to kill these pests, which involves trapping and shooting mainly. We don’t use poison much – because of its persistence in the environment and secondary kill – and have been rewarded now with so many birds and beneficial insects. Our methods are simple and they work. Rats are simply trapped using Fenn traps and need not be a problem. Same with all the other invasive ferals.

We believe it would be worthwhile to fence our orchard completely from these predators, so we can further encourage other more beneficial indigenous fauna. We have begun assembling materials for an “everything proof” fence around our entire farm (donations welcome to assist with this project). We plan to use our orchard and farm property not only to grow food sustainably, but to provide a safe habitat for local endangered flora and fauna. We need areas that will act as reservoirs for recolonising other areas where the native biodiversity has been destroyed by feral pests.

 

Fertilising

The willy-nilly application of fertilisers can lead to problems, like the cadmium build up common here in New Zealand. It is so common that lots of our export crops have to be eaten here because they fail stringent export testing (we have no such testing requirements in New Zealand). There is a wealth of information to say that cadmium in phosphate fertiliser – including Organic brews – has built up in our soils, herbage and produce to alarmingly high levels. The signs have been showing up strong and clear in fish – they literally breathe the water running off our farms. This badly impacts upon the fish closest to estuaries, especially affecting shellfish like mussels and oysters (read MP Sue Kedgley’s Eating Safely in a Toxic World for more details). We believe in applying only what has become deficient in the soil, and we discover what is deficient through careful observation of the foliage, testing and our increasing knowledge of this particular site. Then we apply what’s needed in the purest form possible.

Our growing methods gradually improve the conditions for our avocados and we think that in time we may be able to equal, or even exceed, the yields of the best orchards in the country as well as providing a sanctuary for precious harried unique indigenous species. We now can sit typing out articles like this on our computer with kukupa (native pigeons) only inches away, pigging out on the kawakawa berries on the other side of the office window! A few years ago, it was all grass and thistles.

Avocados are multipurpose perennial trees that live for years – they not only nourish us from the inside out, but make the best face packs, hair and skin conditioners and (not only in California but Tai Tokerau/Northland as well) are the best for naked “Twister” or sliding around on rubber sheets!

 

“Our life is frittered away, by detail – simplify, simplify it”
– Henry David Thoreau

Tim and Zelka Vallings farm a 35-acre property in Maungakaramea, growing avocados and other subtropical fruit as well as being co-partners in Forest Floor native tree nursery.