As cherry growers move towards high density production systems, their main goal is more precocious flowering on young branches for early yields and quick economic returns, Bas van den Ende* writes.

With the exception of some size-controlling rootstocks such as Gisela 5, most cherry rootstocks available in Australia impart strong vigour on the scion (variety).

Generally, cherry trees are vigorous and want to grow upright. They are also rarely willing to form lateral branches. The only branches that a cherry tree naturally develops are those around the tip of strong shoots. This growth habit makes it difficult to make trees fruitful early, unless special chemical and cultural methods are used.

If you try to tame a cherry tree by frequently pruning it, you develop many new shoots, which are often not fruitful and crowd the canopy. Crowding causes shading. Cherry trees are very sensitive to shade. If trees have yellow leaves inside the canopy in mid-summer, it is usually a sign of not enough sunlight getting through the trees.

Achieving early production

To make cherry trees productive early, you must first change their growth habit from being apical dominant (strong in the head, weak in the base). This can be done within three years from planting by forcing trees to develop proleptic shoots and then correctly positioning these shoots so that they become permanent productive fruiting branches. Proleptic shoots are one-year-old and older.

Painting the upright leaders with a mixture of dark acrylic paint and Cytolin at bud-swell, notching and bud thinning are methods you can use in spring to develop lateral shoots.

Whatever high density tree training method you use, make sure that all the future fruiting wood is about as thick as a pencil.

Singulating the tips of the leaders is a job for late spring. As the season progresses, tree training and branch manipulation during the first and second year take increased importance.

When this is done and the trees have become basal dominant instead of apical dominant, it is important to keep the trees calm. You can successfully do this by keeping the trees thirsty after harvest.

When the vigour of thirsty trees slows down and shoot growth has stopped, flower buds form on branches that receive adequate sunlight. Restricting water to cherry trees after harvest, also called regulated deficit irrigation or RDI, is the most important strategy to control vigour and sustain productivity.

Here are some tasks you need to do to make new lateral shoots fruitful:

- Use a mild water stress immediately after harvest to keep the new shoots quiet

- Stub the thick shoots

- Cut about one-third off any long horizontal shoot you want to turn into fruiting wood

- Remove any weak thin shoots

- Keep the trees at the correct height

- Do not prune cherry trees when dormant, because of the risk of bacterial canker infection.

However, if Mother Nature does not cooperate, you could use as back-up foliar sprays of paclobutrazol, sold in Australia as Payback, to stop extension growth. Always read the label to ensure that paclobutrazol is registered wherever your orchard is.

For more details on the chemical and cultural methods, go to orchardmanuals.com – Sweet Cherries – Orchard Management.

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