Limiting Factors in Growing Apples in the Tropics

 By Kevin Hauser

Kuffel Creek Apple Nursery

When an article is published about our nursery supplying apples to the tropics, inevitably we will get several emails from interested parties in other tropical locations asking if I think apples will grow there also.  This paper is intended to help explain the limiting factors in growing apples in the tropics.

 Nigerian Study

 In the early 1990’s a study¹ was done in Nigeria and Southwest Cameroon over three years in strictly tropical zones consisting of 18 sites in Nigeria and 8 in Southwest Cameroon, intending to find sites appropriate for apple cultivation.  Apples have been grown for years in cooler tropical highlands, but this study focused on hotter tropic lowlands.  They also tested 100 apple varieties from the Voinesti Research Station in Romania for suitability to the tropics.  They compared growth habit and yield from the different areas and plotted them on a matrix, as well as testing different methods of culture.  As a benchmark of a successful highland apple growing areas they used the Batu region of Indonesia and Baguio and Spencer Farm in the Philippines , as well as Kitale in Kenya .

 Heat and Chilling Hour Units

 Two elements that were not limiting factors were heat and chilling hour units, the number of hours between freezing and 45 degrees F (7C).  Even here in Riverside we have found that well-watered apple trees can tolerate a great deal of heat (115 degrees F or 46 C is common here during our hottest month). Many varieties can endure this heat even during ripening times, and still be productive and attain good quality.  In the tropic lowlands the temperature never does get below 45 degrees F (7 C) and so the apples will receive zero chilling hours, so the chill-our rating of the variety is mostly irrelevant.  However in tropic apple culture, after cropping any irrigation is shut off and the leaves on trees are stripped manually by hand.  This has the affect of making the tree think that it has gone through a period of dormancy and chill need (whatever it may be) has been satisfied.  After 6 weeks irrigation is started up again, and coupled with consistent day length and temperatures in the tropics, the tree then thinks that it is spring and starts the blossom and fruiting cycle anew, typically falling into a pattern of fruiting twice a year.  Different apple varieties respond better to this tropic apple culture, which is more important than being “low chill”.  Oddly enough Rome Beauty responds quite well to it and is very popular in Indonesia , even though it has traditionally been considered to have a high chilling requirement. 

 Rainfall

 The biggest limiting factor turns out to be excessive rainfall during blossoming period.  Excessive inundations of rainfall damages the flower petals, prevents pollinating insects from flying, decreases the fruit set, causes premature fruit drop, and spreads foliar disease.  The best areas are those that are relatively drier but have the potential for irrigation, which can be used to control the fruiting cycle.  Areas with moderate rainfall can also be suitable if the young trees receive sufficient water to establish them.  Drier areas lacking irrigation are difficult to establish orchards in, as typically the water has to be hauled by hand from a bore hole until the trees are mature enough to reach the underground water table, a heavy and difficult task.

 Soil Fertility and Location

 Apple trees actually prefer low nitrogen and have the ability to grow in poor soils if cultivated deeply and well-drained (however quality and yields will increase if the soil is subsequently fed and cultivated).  Standing water for long lengths of time will damage the tree roots, but vigorous rootstocks can tolerate sandy and heavy clay soils.  It has been a standard practice for years to till vegetable and grain crops in the flat areas and plant orchards on hill sides, with or without terraces.  In alkaline soils where cotton has been grown before they are susceptible to Cotton Root Rot (Phymatotrichum omnivorum) which will require lowering the pH of the soil before planting, not always an easy task.  Apples can tolerate acidic soils fairly well.  In areas where wooly aphid (family Eriosomatidae) is present in the soil apple trees should be grafted onto wooly aphid-resistant rootstock such as M111.  Apple trees require full sun exposure for at least 8 hours a day.

 Interplanting Crops

 Shallow-rooted crops that do not require deep cultivation such as beans, berries, and Irish potatoes can be planted between the apple tree rows until they start bearing apples.  This will also depend on the water availability and soil fertility.

 Best Varieties for the Tropics

 The apple has great genetic variability and thousands of varieties exist, many of which have been shown to be adaptable to tropical environments.  I have identified at least 20 varieties that may be commercially important in the tropics and am undergoing testing of them in several places in equatorial Africa .  Emphasis has been places on fruit quality, color, productivity, and disease resistance.  Some like Anna and Dorsett Golden have been successfully grown in the tropics for years.

 Risk of Loss

 Whenever introducing a new crop to an area that’s never grown it before the enterprise should be considered speculative, as all the conditions cannot be known until the crop has been grown for many years.  The farmer should be prepared to experience 100% loss of the investment (which has happened many times).  Many areas that have started growing apples have lost whole orchards multiple times before discovering culture methods that allow the orchard to be successful.   That being said it should be noted that just because growing apples is harder in your location, doesn’t mean that it cannot be done.  Growing apples is hard in many colder climates also, and 100% loss of a season’s crop is quite common even in the best growing areas due to harsh weather or insect and disease damage.  Yet the financial reward of a good harvest of a fruit in high demand can encourage innovative ways of growing apples in unlikely locations.

 ¹Apple Production in Strictly Tropical Zones: First Observations in Nigeria , Prince Nduka Alum and Romana Magherini, Acta Horticulturae 409, 1995, Temperate Zone Fruits IV