Fruit trees: basics and beyond

If you’re new to growing fruit trees you might find some of the commonly used terms and phrases a little bamboozling at first! Here’s a breakdown of some of the most frequently used terms and what they mean.

Basics

Growing terms

• Dwarf or semi-dwarf: Trees with a compact size at maturity usually because they have been grafted onto dwarfing rootstock. Ideal for home gardens.
• Grafting: The process of joining two different plants together, usually the top section of one tree with desirable fruiting traits onto the roots of another, to create an improved tree. Sometimes several different fruit varieties are grafted onto a single rootstock, which can be a great space saver.
• Rootstock: The root system selected for grafting to control size, improve hardiness or disease resistance, while the grafted on top determines the fruit you harvest.
• Suckers: Leafy growth or shoots that appear below the graft. Remove these or else the rootstock plant can take over, reducing yield and vigour.
• Root zone: The area where the roots have spread, generally to the outer edge of the tree canopy.

Climate & seasonal terms

• Chill requirements: This refers to the total hours below 7°C a deciduous fruit tree needs over winter to wake up properly and fruit well. You’ll see this listed as hours, units, or simply low, medium or high chill. Low-chill trees need less cold, making them a good choice for warmer areas.
• Frost tolerance: How well a fruit tree copes with frost from ‘no frost tolerance’ to ‘light frost tolerance’ and then ‘heavy frost tolerance’. Some, like avocadoes citrus and mangoes, may require protection in early years but develop tolerance as they mature.
• Dormant season: For deciduous trees from late autumn when leaves have fallen, to early spring when flowers and leaves emerge. This will impact on maintenance and pruning.

Pollination terms

• Self-pollination or self-fertile: Where pollen moves within the one tree. Many fruit trees, including citrus and peaches, are self-pollinating using their own pollen to produce fruit.
• Cross-pollination: Requires pollen from a different tree of the same type. For example, apples and most plums require cross-pollination from a compatible variety, so you’ll need two trees to produce fruit. A compatible variety is often called a ‘pollinator partner’.
• Fruit set: The successful transition from flower fertilisation to a baby fruit.

Life cycle & fruit formation terms

• Bud swell: When new flower and leaf buds become plump in late winter and early spring but have not actually opened.
• Bud break: When the buds break open, revealing new leaves or flowers.
• Winter clean up spraying: Typically a lime sulfur or copper spray applied before bud swell and again before bud break to control or prevent various pests and diseases, including stone fruit leaf curl.
• Thinning: Removing excess immature fruit to improve size and quality of the remaining fruit.
• Biennial bearing: When a tree produces an abundant crop one year and a poor one the next year. Common in mandarins. Thinning can help reduce biennial bearing.

Pruning terms

• Canopy: Upper part of the tree, including branches and leaves.
• New wood: Branch and stem growth in the current year.
• Old wood: Growth from previous years. Most fruit forms on wood that is least one year old.
• Fruiting spurs: Short side shoot on a branch where flowers develop on some trees. For example, apples and pears mainly fruit from long lasting spurs on their old wood.
• Summer pruning: undertaken in summer after fruit is harvested with the aim of controlling tree vigour.
• Winter pruning: Structural prune when deciduous trees are dormant to shape the tree for better airflow and fruiting.
• Training: Any pruning or bending done to shape growth into a specific form, such as an open vase-shape or espaliered against a wall.

Did you know?

Bananas are not fruit trees! Technically they are a herbaceous perennial that produce a berry (the banana fruit).

Beyond

Science behind fruit formation

• The process starts in the stamen (the male part), where pollen is produced in the anthers, which are supported by the filament. The pollen is transferred by wind, insects or birds to the stigma at the top of the pistil (the female part). The pollen then forms a tube that grows down the style to the ovary and fuses with ovule(s) to form seeds. As the seeds develop the ovary wall enlarges into the fruit flesh. For most fruit, fertilisation is essential but for some, such as most figs, they can form without fertilisation through a biological process called parthenocarpy.
• The basic structure of a fruit includes three layers collectively called the pericarp. The outer skin is called the exocarp, the fleshy middle layer is the mesocarp and the inner layer, often hard or stony, is called the endocarp.

Fruit types

Fruit types vary based on how the pericarp, or layers, develop.

• Drupes, like peaches, cherries and plums, have a fleshy mesocarp and a hard, stony endocarp enclosing a single seed. Most drupes have superior ovaries, where the ovary sits above the attachment point of the petals, sepals and stamen.
• Pome fruit, like apples and pears, originate from an inferior ovary, which sits below the attachment points for petals, sepals and stamen (as pictured above), their core surrounds the seeds, and the surrounding edible tissue becomes fleshy.
• Berries, such as grapes, have a soft pericarp throughout, with seeds embedded in the flesh.