Mango seedlings as a rule start to bear fruit within 4–7 years, while grafted trees (if allowed) may bear a few fruits in their second year in the field. Mango production in Kenya has to be differentiated according to the production system. There is traditional mango growing, and commercial and market-orientated mango cultivation. Out of an average annual mango production in Kenya of about 140,000 tonnes (t) during 1999/2000, approximately 3300 t (2.3%) were exported (source: Annual Report, Horticultural Crops Development Authority (HCDA), Ministry of Agriculture, Nairobi). Some distinct differences between the location of production and the performance of the orchard can be identified, such as the harvest period, the fruit quality and the yield level. Due to the varying ecological conditions in Kenya, mangos are available almost all year round (see Appendix 3 - Provincial Mango Production Stats).
In the main production area, the Coast Province, two supply seasons can be differentiated. The first and main season runs from November to February and the second from June to August. In areas of higher altitude such as Murang’a and Mwea (Central Province), the harvest season is 4–6 weeks later than at the coast, with a peak in February and March. The mango picking season in Kenya competes with that of other mango producing countries (Mexico, Brazil, India, Pakistan, Israel, South Africa) and extends over a period of between 5 and 6 months (see Appendix 4 - Supply Seasons of Mango Exporters). Interestingly though, Kenya exports only about 3000 t out of the worldwide export tonnage of 580,000 t/year (FAO, 2001).
Productivity depends on a number of factors, including quantity of previous crop, weather and soil conditions, altitude, control untreated subjects used for comparison with those given a particular treatment of pests and diseases, fertilization pollination and cultivar variety, type. Even in the case of the same cultivar, yields vary greatly because mango is grown under widely varying agroclimatic conditions and cultural practices.
Biennial or irregular bearing occurs often with the mango and it is common for some cultivars to bear heavily in one year and sparsely the next. One of the reasons for this phenomenon is that trees over-bear in one year, thus inhibiting adequate flower bud formation the following year. Under these circumstances, it is difficult to get accurate local long-term yield records. However, it is well known that yields of 25 t/ha and more for Kent, Sabine, Tommy Atkins and Keitt are not uncommon.
Cultivar trials carried out under rainfed conditions at government prison farms in Kenya indicate that even higher yields could be achieved. Table 1 and Table 2 show the performance of some imported mango cultivars planted in the Central Province of Kenya. Additional performance figures are also shown in these tables which are taken from Griesbach (1992, page 87).