Persea americana Mill.

Persea americana, the Avocado, is the best-known species in the genus, cultivated throughout warm temperate and tropical areas for its large, nutritious fruit, consumed by itself or as a component in salads. The ease with which its seeds germinate (whether or not supported by crossed toothpicks over a glass of water) makes it a popular novelty subject, and the resultant seedlings are sometimes planted in temperate gardens – usually to be killed promptly by frost. Indeed, its inclusion in this book might seem dubious, but for the fact that there are several trees growing and fruiting happily in central London. A more striking example of the effects of microclimate could hardly be sought: Johnson (2007) mentions trees in Chelsea (6 m) and Stepney (4.5 m), while Martin Gibbons of the Palm Centre, Richmond (pers. comm. 2006) has drawn our attention to another in Ladbroke Grove. This one was about 5 m tall and rather broad at the base, fully clad in healthy dark green foliage and bearing many unripe fruits when observed by Martin Gibbons in July 2006. These specimens are, of course, exceptions, but they demonstrate the point that plants may well be ‘worth a try’ and that with care, and/or luck, boundaries may successfully be pushed when planting marginal species. Hogan (2008) comments that similar individuals can be found in western American cities ‘between freezes’, but that the species is more generally successful on the southern Oregon coast, specially around the mild enclave of Brookings. Similarly, there are substantial trees in Cornwall and on the Scilly Isles. For those of us who do not garden in such benevolent areas, however, the climate will have to change dramatically before we can safely plant P. americana (for which any persistent frost is a danger). A useful summary of Avocado culture under commercial conditions is given by Huxley et al. (1992).