Avocados

Start with the box

Steve starts every crop with one question: tell me what your market wants. With avocados, the real answer comes days or weeks after the pick, when the fruit ripens. Good fruit softens evenly to clean, buttery flesh, with no rots, no grey or stringy flesh and no bruising. Add the size the buyer wants, a clean skin, and enough oil to pass the dry matter test, and that’s what the box is paid for. The test finds how much of the flesh isn’t water. That tracks the oil.

An avocado can look perfect on the tree and still break down in the box. So the profit isn’t the tonnes on the tree. It’s the fruit that arrives sound and ripens well: Steve calls that recoveries. And a lot of it is settled in spring, months before the pick.

The end of an avocado branch late in the season: three big, dark green, pebbly avocados hanging below its leaves, and at its tip, flower spikes of tight cream-green buds. — An avocado can look perfect on the tree and still break down in the box. What the box is paid for shows days or weeks after the pick, when the fruit ripens: good fruit softens evenly to clean, buttery flesh, with no rots, no grey or stringy flesh and no bruising. So the profit isn’t the tonnes on the tree. It’s the fruit that arrives sound and ripens well, and a lot of it is settled in spring, months before the pick. An illustration, simplified.

A ripe avocado cut in half lengthwise: its big round seed in one half and the hollow where it sat in the other, the flesh clean, creamy yellow shading to green under a dark, pebbly skin. — An avocado can look perfect on the tree and still break down in the box. What the box is paid for shows days or weeks after the pick, when the fruit ripens: good fruit softens evenly to clean, buttery flesh, with no rots, no grey or stringy flesh and no bruising. So the profit isn’t the tonnes on the tree. It’s the fruit that arrives sound and ripens well, and a lot of it is settled in spring, months before the pick. An illustration, simplified.

A tree full of flowers

A grown avocado tree can open up to a million flowers in a spring, and only a few hundred of them become fruit. Each flower opens twice. It opens first as a female, ready for pollen, then closes, and opens again about a day later as a male, shedding pollen of its own. So the set depends on warm, settled days, and plenty of bees moving from flower to flower. A cold snap, or a hot, dry wind, at flowering costs fruit.

Look closely at one flower on each of its two openings. The first time, it opens as a female: its stamens lie flat out on its petals, and the white tip of its pistil stands up in the middle, ready for pollen. By the second, a day later, that tip has browned and closed, and the stamens stand up round it, shedding their pollen. So a flower’s own pollen comes too late for it. What sets it is pollen from another flower, open as a male, carried across by the bees.

One avocado flower, magnified: six pale yellow-green petals spread flat, a white-tipped pistil standing in the middle, and the stamens lying flat out on the petals. — Each avocado flower opens twice: first as a female, then, a day later, as a male. Its own pollen comes too late for it, so the bees have to carry pollen from flower to flower. An illustration, simplified.

The same avocado flower a day later: its stamens stand upright round the pistil, their heads open with yellow pollen, and the pistil’s tip has turned brown. — Each avocado flower opens twice: first as a female, then, a day later, as a male. Its own pollen comes too late for it, so the bees have to carry pollen from flower to flower. An illustration, simplified.

Flowering sets the crop. Boron has to be there for the pollen to grow down to where the seed will form, and calcium for the flowers and the set. A crop that sets short can’t be made up later.

The flush and the fruit

Here’s the avocado’s own twist. As the fruit sets, the tree flushes. On most flower spikes, a new shoot grows straight out of the spike’s tip, past the fruitlets, with soft bronze leaves. The tree is setting its crop and growing its new leaves at the same time, on the same shoots.

Both want calcium, and calcium goes where the water goes. Young leaves breathe out far more water than a fruitlet does, so they pull most of it, and most of the calcium with it. The fruitlets get what’s left, in the very weeks they’re making their cells. A fruitlet is richest in calcium about six weeks after set. After that it keeps taking a little in, but it grows faster than the calcium comes, so what it has is spread thinner. And it’s that calcium that holds the fruit together in the box.

The end of an avocado branch at fruit set: two dark green older leaves, a flower spike with three small green fruitlets, and from its tip a flush of soft, bronze-red young leaves. — In spring the fruit sets while a new flush grows from the tip of the same spike. Its young leaves pull most of the water, and the calcium goes with it. An illustration, simplified.

Steve’s rule of thumb is that the cell division window in avocados runs three to four weeks, where in beans it’s days.

And an avocado keeps making cells, more slowly, for as long as the fruit grows. So the calcium has to keep coming, week after week, right through fruit set, and the flush is pulling against it the whole time.

That’s where nitrogen comes in. Nitrogen at flowering feeds a big, soft flush, and a bigger flush takes more of the water, more of the calcium, and more of the tree’s sugar too. Steve’s line that nitrogen is a liability until it becomes a protein means something very plain here. Hold it back while the fruit sets, and give it when the tree can use it: as the fruit sizes, and after the pick.

It’s Steve’s order, on a tree. Pour the foundation before the flowers open: calcium, boron and silicon. Keep it coming through the set. Then fill the house with potassium, once the fruit is sizing.

Roots in the mulch

Avocado roots are shallow and fine, with few root hairs. Most of the roots that feed the tree are in the top of the soil and the mulch on it. The tree comes from forest country, where the ground is deep in fallen leaves, and it still roots as if it were there. Mulch keeps those roots cool, moist and fed, and feeds the life around them. Pull the mulch back, and look: you want plenty of fresh white root tips.

The same roots can’t stand wet feet. Waterlogging starves them of air, and root rot, the avocado’s worst disease, gets in where the ground stays wet. That’s why avocados go on mounds or well-drained slopes, and why growers keep the soil mulched and up in calcium to hold the rot back.

The ground under an avocado, cut away: fine roots spreading through the top of the soil and up into a thick mulch of fallen leaves, many with fresh white tips. — Avocado roots are shallow and fine, and most of those that feed the tree are in the top of the soil and the mulch on it: pull the mulch back, and you want plenty of fresh white tips. The same roots can’t stand wet feet. Waterlogging starves them of air, and root rot gets in where the ground stays wet. An illustration, simplified.

The same ground waterlogged: water over soggy mulch, the soil grey and wet, the fine roots brown and black with no white tips. — Avocado roots are shallow and fine, and most of those that feed the tree are in the top of the soil and the mulch on it: pull the mulch back, and you want plenty of fresh white tips. The same roots can’t stand wet feet. Waterlogging starves them of air, and root rot gets in where the ground stays wet. An illustration, simplified.

Avocados are also among the trees that mind salt the most. Salt in the water burns the leaf tips and edges first, and a burned leaf feeds the fruit less. The Stress and salt page has more.

Size, and oil

Many fruitlets drop in the weeks after set. That’s the tree matching its crop to what it can carry, and a hot, dry spell or a hungry tree drops more. Once the drop is over, the fruit sizes through summer. That’s sizing, and it’s where potassium has earned its place: an avocado holds more potassium than any other mineral.

The oil starts building a few weeks after set, alongside the sizing. It keeps building on the tree right up to the pick. In late summer or autumn the tree flushes again, with the fruit still building oil. The dry matter test follows the oil, and says when the fruit is ready to pick. An avocado never softens on the tree: it only ripens once it’s picked. So the tree can hold its fruit for weeks, even months, like a cool room.

That has a price. Fruit left hanging is still drawing on the tree while next season’s flowers form, and a heavy crop picked late is one way into the on years and off years that the Tree crops page describes. After the pick, give the tree back what it spent, before it flowers again.

The same branch a few weeks later: the avocados picked, the flower spikes finished, mostly bare, with one small green fruitlet, and a flush of bronze-red young leaves at the tip. — An avocado only ripens once it’s picked, so the tree can hold its fruit for weeks, even months. That has a price. Fruit left hanging still draws on the tree while next season’s flowers form, and a heavy crop picked late is one way into on years and off years. An illustration, simplified.

The season at a glance

A year, from 1 July, as the program builder starts a tree. The months are a guide: your district can run weeks earlier or later, and the tree’s stage is the clock. Build yours in the program builder.

1 · Winter: flower buds early July to mid-August

Next spring’s flowers are forming now.

How you know it’s here Fat, rounded buds at the shoot tips, plumper than leaf buds, starting to swell.

What matters most: Boron Zinc Calcium
2 · Flowering mid-August to mid-OctoberSap test

Boron and calcium for pollen, flowers and set.

How you know it’s here The flower spikes open out, and the tree is covered in small greenish-yellow flowers.

What matters most: Boron Calcium Zinc
3 · Fruit set and cell division mid-October to mid-DecemberSap testCell division

Most of the fruit’s calcium gets in during these weeks, so keep it coming.

How you know it’s here The petals fall, and pea-sized fruitlets hold on the flower spikes. Many will still drop.

What matters most: Calcium Boron Silicon
4 · Fruit growth mid-December to mid-March

Sizing through summer. The fruit has earned its potassium now.

How you know it’s here The fruitlet drop is over, and the fruit is sizing up.

What matters most: Potassium Magnesium Nitrogen
5 · Autumn flush and oil mid-March to mid-May

Keep the engine running as oil builds in the fruit.

How you know it’s here A new flush of leaves in autumn, and the fruit near full size, still building oil.

What matters most: Potassium Manganese Magnesium
6 · Harvest and recovery mid-May to late June

Pick, then give the tree back what it spent.

How you know it’s here The fruit passes its dry matter test, and picking starts.

What matters most: Nitrogen Calcium Boron

Where it fits in a program

Write down what your packer and your market pay for, and what comes back as rejects.
Have calcium, boron and silicon in before the flowers open, and keep the calcium coming through fruit set.
Hold the nitrogen back while the fruit sets. Give it as the fruit sizes, and after the pick.
Save potassium for sizing, through summer. By then the fruit has earned it.
Keep the mulch on, the ground drained, and an eye on the salt in your water.
Sap test before flowering and through the set, and compare each with last season’s. On each walk, count the fruitlets on a few marked branches: how many hold, and how they size.

“Here’s the thing with cell division. Orchard crops, or other crops like limes and avocados, they probably have more of a three to four week window.”

— Steve, on cell division in tree crops

Avo­ca­dos