The three parts of the fruit, the seed, the stone and the flesh, develop separately over time, and fit in with other growth patterns of the tree, such as growth of new shoots and roots, Bas van den Ende* writes.

An understanding of the development of these parts of the fruit will help you to schedule your irrigation, to time your thinning, and to maximise size of fruit at harvest.

RDI

Many orchardists have heard of RDI (Regulated Deficit Irrigation). RDI can save water and money by reducing irrigation and pruning. Although under RDI, trees are purposely stressed for water, the words Regulated Deficit Irrigation imply, that RDI is not a haphazard neglect of irrigation, but a carefully planned irrigation strategy.

RDI aims to manipulate the seasonal growth pattern of the trees and channel more tree resources into fruit rather than into shoot growth.

RDI only for selected crops

With some fruit crops, such as canning peaches and late maturing market peaches, nectarines and plums, fruit and shoot growth are out of phase, that is, they grow at different times.

RDI can be applied to these fruit crops because the growth of new shoots can be controlled without affecting the growth of fruit.

With peaches, nectarines and plums that mature early in the season, and also cherries and apricots, fruits and shoots grow at the same time, and RDI is not recommended.

Different parts of a stone fruit, for example the peach.

Fruit growth stages

Cell division

After flowering and fruit set, there is a period of several weeks when cells are formed in the flesh and stone. This is called the period of cell division.

Stone hardening

Following the period of cell division, the tree will look after the reproductive part of its fruit, namely the seed.

A hard shell around the seed, called the stone, protects the seed from getting damaged.

As the seed grows to its full size, the stone hardens (lignifies) around the seed. This is called the period of stone hardening.

Cell expansion.

When the stone has lignified and the seed is fully developed, the trees will fill the cells of the flesh with sugar and water.

This is the period of cell expansion and is usually much longer than the period of cell division.

Final swell

Cells expand rapidly, especially towards the end of the growth cycle when time of harvest approaches.

This is called the final swell, and the demand for water by the tree is high.

The growth curve and development of stone fruit during the season. For cherries and apricots, the growth curve
and development of the fruit are contracted into about 90–100 days. In other stone fruit, such as the peach,
shown here, the growth curve and development of the fruit can extend to as much as 200 days.

Leaves

The leaves have to work hard to produce the carbohydrates that form sugar. The leaves can only work hard if the tree can capture plenty of sunlight and this sunlight can penetrate through the canopy. This is where pruning and trellis design comes in.

Follow the growth cycle

By cutting several fruit through the suture line with an anvil-type pair of secateurs, you can follow the growth cycle of your fruit and determine when you should apply RDI, where applicable, and also when you should start and finish thinning.

You can also determine when the fruit reaches ‘final swell’.

Thinning fruitlets or flowers

Thinning fruitlets is one of the most expensive and labour-intensive exercises.

Thinning fruitlets also exacerbates the incidence of split stone.

More and more peach and nectarine growers are starting to realise that size of fruit at harvest can be greatly improved by target pruning , thinning flowers by hand, or thinning flowers chemically, cincturing the trunk of the tree, and timely thinning young fruit by hand.

Varieties that mature early and/or are hard to size, benefit from flower thinning.

To thin flowers and fruitlets to obtain the sizes of fruit that the markets demand, you must know how the fruit of different varieties behave.

Fruit set, premature fruit drop and ‘doubling’ are factors you must put in the equation when you regulate your crop. By periodically examining your peaches and/or nectarines, you take much of the guesswork out of managing your orchard.

*Bas van den Ende was a researcher at the Tatura Research Institute, author, and former consultant in fruit production. Contact: advhort@bigpond.net.au