John and Jacky Marshall live in Whitfield, Cairns, but grow their fruit trees on the family farm at Kuranda. They have 160 acres, with an orchard of hundreds of durians, rambutans, mangosteens and many other exotic fruit trees. The Skyrail cableway passes over the edge of the farm, very close to the Barron Falls. John said that 30 years ago, when he planted his first 100 durian trees he followed the advice of the so-called experts. Ninety per cent of those trees eventually died, from a variety of factors. Mis-information and misleading management advice was the main cause. After 10 years of learning the hard way, the 90% failure rate has now been turned around to a 90% success rate, because John now grows his trees under natural conditions, such as they would experience in their natural habitat.
When planting fruit trees of any type John never introduces fertilizer or mulch into the hole, because fertilizer is always too strong and burns the new roots, retarding growth. Mulch encourages fungal attack on the new roots causing root-rot. He fills the hole around the plant with only the best top soil, eg. the top one centimetre of surrounding soil (minus the leaf-mould). When leaf mould breaks down it produces two chemicals that inhibit root growth. Leaf mould is essential for healthy top soil under the tree, but should be kept to a maximum of 3 or 4 cms thick, and away from the trunk. A thin layer of leaf mould helps to keep soil moist and promotes healthy bacterial colonies. He says that constant soil moisture is very important when trees are developing a crop. Most fruit-drop is caused by irregular watering, allowing soil to dry out in between water applications.
Durian, rambutan and mangosteen usually flower within 3 weeks of each other, towards the end of the northern summer. Durian is the only one of these 3 fruits that has to be hand pollinated. Some varieties of durian will self-pollinate but set only a few fruit, whereas hand pollination can produce up to 120 fruit on a large tree.
Fruit orchards throughout the world suffer biennial or triennial bearing, ie. they tend to crop only every 2nd or 3rd year. The main reason for this is that the trees are being grown away from their natural latitude, eg, a mangosteen that fruits annually on the Equator will fruit less often at the latitudes of 15 - 18 degrees north or south, such as the Innisfail areas of North Queensland.
Durian take about 4 months to mature and fall off the tree naturally when they are ripe. They usually fall around dawn. Most durian fruit is sold to the large population of S.E. Asians who live in the Far North.
Longan is one of John's favourite fruit. However, by experience he has found that grafted longans are usually not very productive. They have small crops and small sized fruit. Longans should be either grown from seed or as marcotts.
Seedling mangosteens can take 10 to 20 years to first fruiting. Grafted mangosteens can fruit within 12 months of being grafted, even while they are still in the pot. However, grafted mangosteen trees will always remain small in size with a corresponding small size crop. Because of this they are not commercial, but ideal for backyard growers. Mangosteen will not grow further south than the Innisfail/Tully area of North Queensland.
Seedling fruit trees can often be brought into fruiting almost as soon as grafted ones, (except Mangosteens). The idea is to grow seedlings of good varieties as fast as possible for 3 or 4 years, then reduce fertilizer to once a year and water-stress (dry soil) them for about one month before they would normally flower. While drying out the soil, do not allow more than about one quarter of the leaves to fall, as the resulting crop will need the support of a good leaf canopy.
Rambutans, mangos and longans etc. can be brought into bearing using this method, when about 5 years old.
In the old days, cincturing of the trunk was used to bring on early flowering, but withholding soil moisture has been found to be a better practice. Seedling fruit trees usually have more resistance to disease and drought, and generally live longer than grafted trees.
John and Jacky grow many other varieties of fruit trees including, Pulasan, Lychee, Imbu, Longan, Duku, Langsat, Mango, Jackfruit, And Salak.
Article compiled by Sheryl Backhouse