(Image Source – Paolo Galli, Wikimedia Commons)
With the ever-increasing interest in food growing worldwide, many people are trying their hand at growing nut trees with great success. Pistachio nuts are very popular, just about everyone loves them, and it’s inevitable that some gardeners will take interest in growing their very own pistachio nuts – which is a terrible idea! Why? Let me explain…
The pistachio nut tree (Pistacia vera) is a member of the Anacardiaceae family, and is related to the cashew, mango, and sumac, as well as the toxic poison ivy, poison oak and poison sumac. Pistachios are a small bushy deciduous tree native to western Asia and Asia Minor,from Syria to the Caucasus and Afghanistan, growing slowly to a height and spread of 10m (30’) when fully grown. As far as nut trees go, they’re considered small, and they can be pruned to maintain a certain height.
Pollination and production
Pistachio trees are dioecious, which means that trees produce only male or female flowers, so you need both a male and a female tree to produce nuts on the female tree and they’re wind-pollinated . A female tree won’t produce nuts unless a male tree is growing nearby, and to maximize the chances of pollination, the male tree is best planted upwind of every 10 to 15 female trees.
Bearing nuts takes a while, as pistachios have a long juvenile stage, they won’t typically produce much nuts for the first five years, and reach full production after 10-12 years. Another characteristic of pistachios is the tendency to biennial cropping, alternately bearing lots of nuts one year, then very little the following year.
These trees are classes as phreatophytes, plants with a deep root system that allow them to mine the soil deeply and draw their water supply from near the water table. This adaptation allows pistachios to survive long periods of drought. They’re also considered to be more salt-tolerant than many other nut and tree fruit species. These attributes are consistent with what we’d expect to see in a arid semi-desert tree.
Pistachios do better in favourable soil conditions, they prefer soils with a pH close to neutral, and they need some soil depth – a potential rooting depth of 60cm (2’) above any clay or lime layers which would restrict the roots.
The biggest restriction in growing pistachios is their climatic requirements. They require long, hot, dry summers and moderate winters. More precisely, to grow and produce nuts they require very hot summers (more than 600 hours above 30 degrees Celsius or 86 degrees Fahrenheit ) and very cold winters (more than 1,000 hours chill hours below 7 degrees Celsius or 44.6 degrees Fahrenheit), which translates to a winter dormancy period about 6 weeks with temperatures below 7 degrees Celsius.
What places have these unique climatic conditions? Arid semi-desert locations do. Pistachios actually do best and produce the most nuts in arid semi-desert climates which have long, hot dry summers with low humidity and cool but not frigid winters. During their growing season, pistachios thrive on heat, with summer temperatures of around 37 degrees Celsius (98.6 degrees Fahrenheit) producing large quantities of the best nuts.
Being semi-desert trees, pistachios dislike humidity during their growing season. High humidity, from summer and autumn rains for example, promotes fungal diseases, which will overwinter on the trees and infect them the following year. Pollination is also affected by strong dry winds, late spring rains and frost.
The reality that prospective growers need to face is that there is very few places that are hot enough in summer and cold but mild enough in winter to grow pistachio nut trees!
In Australia, the northern states with their hot subtropical and tropical climates aren’t cool enough in winter, and the colder temperate southern states don’t get summers that are hot enough or long enough for reliable production, and they often don’t get enough chill hours either!
Just to show you how limited the locations for growing pistachios are across all of Australia, I’ve provided an extract and map from Pistachios – “A Handbook for Farmers and Investors, Rural Industries Development Corporation, Australia.
What we find is that “Australia’s production of pistachio nuts and fruit is only about 25% of current domestic sales.Most nuts for the Australian market come from Iran and the USA. The major areas of commercial pistachio orchards are along the Murray River in NSW, Victoria and SA, but there are other orchards scattered through southern and central NSW, Victoria and the SA mallee. There is some interest in development of the crop in WA.”
Looking at the maps, the four tiny orange spots around the northwest corner of Victoria and adjoining states are the only places that actually do produce pistachios in all of Australia, while it may be possible in the zones marked in green but it hasn’t been done yet.
To grow or not to grow, that is the question. Hopefully with this information, gardeners can make a better informed decision about whether it’s viable to grow semi-desert nut trees where they live!
Unless you live in a location that can provide a pistachio tree’s requirements and have space for two trees, my recommendation would be to choose a more appropriate nut tree which is less challenging and better suited to the climatic range where it will be grown.
Pistachio Production Manual, Fourth Edition 2005, University of California, Department of Plant Sciences, College of Agricultural & Environmental Sciences
Pistachios – “A Handbook for Farmers and Investors, Rural Industries Development Corporation, Australia
Growing Pistachios – Pistachio Growers’ Association