One of the lesser known but nevertheless delightful tropical fruits which is relatively easy to grow is the Sugar Apple. It is often called Custard Apple, and it belongs to the botanical family, Annonaceae.

The species like so many other exotic fruits, originated in the tropics of South America. They were obviously well-known to the early inhabitants of that continent, as it is now widely scattered in places like Mexico, West Indies, India, Spain, Israel and Australia.

This sweet, delicious fruit is heart-shaped, 3 to 4 inches in diameter, skin bumpy and green with juicy, sweet, white flesh, neatly encasing several shiny black seeds. The fruit is classed as excellent.

The trees are semi-deciduous, shedding a large portion of their leaves by the end of winter. They are usually an open tree; fairly small, but often grow to around 5 metres tall. Flowering usually occurs first in spring after bud burst, but very few of these flowers set fruit. Sometimes a poor set of misshapen fruit will occur, mainly due to poor pollination. Humid weather seems to help pollination, and further flowering after spring seem to have a better fruit set.

Being a tropical plant, they require a fairly hot climate, such as coastal regions of northern NSW and Queensland. In such areas the temperatures are not excessive, and there is normally sufficient humidity during the flowering period to ensure a good crop. Young trees must be protected from frosts but when mature, will usually withstand light to moderate frost.

Lighter textured soils which are well-drained and will grow bananas successfully, are quite suitable for the sugar apple. Care should be taken that the soil is well-drained. Mounding is a good idea when soils are of heavy clay. The amount of water applied during the growing season will depend on the frequency and extent of the rainfall received. When rainfall is low, the trees should be regularly and thoroughly watered, but care must be taken to avoid excessive watering, as it may cause the onset of root rot.

The sugar apple responds to regular application of nitrogen, phosphorous and potassium.

As they are also a member of the Annonaceae family, zinc deficiency symptoms are frequently seen in the form of stunted shoot growth, with small mottled leaves. Zinc deficiency can normally be corrected by spraying the trees in spring with a mixture of 10 grams of zinc sulphate in 10 litres of water. Sometimes a follow-up spray will be required again the following spring.

Seedlings usually come into flowering when three to four years old. Some are more productive than others and there is much variation in the size and quality of fruit produced by different trees. When there is an unusually good tree, it should be propagated by budding on to sugar apple seedlings.

Pruning of mature trees involves cutting off any branches which crowd the centre of the tree, and any other whip-like shoots are shortened back. After bud burst is the best time to prune, when the sap flow has begun. Fruit is produced on shoots which grew the previous season, as well as those which grew two years earlier.

The best way to pick the fruit is when it matures. That is when the spaces between the segments fill out and become lighter in colour. The fruit should be clipped from the tree level with the shoulder of the fruit while the fruit is still firm, then allow it to ripen at room temperature. If the fruit is harvested too early, it will not ripen and soften properly.

Although only a minor crop in our northern states, there appears to be little reason why more of this fruit should not be grown, as this delightful fruit should easily find a ready market.