Let’s be frank: the confusion about avocado flowers and their pollination is well justified. Their reproductive habits are as mysterious and romantic as a magical realism novel, fascinating but sometimes hard to follow. It’s fitting because these trees originated in the warm, humid climes of Central and South America. As far as floral gender goes avocado flowers are classed as botanically ‘perfect’, that is, they have male and female parts in the one flower. The mysterious thing is that in its natural climate (South Central Mexico and the like) these parts are usually active at different times of the day, so the whole plant has a female phase and a male phase. This reduces the likelihood that one tree will pollinate itself, thus ensuring greater genetic seed diversity.
Avocado trees are usually classed as either A or B varieties. A varieties will open as female in the morning of the first day, and male in the afternoon of the second day. B varieties will open as female on the afternoon of the first day and male in the morning of the second day.
So in their natural climate you would plant an A and a B variety to ensure insects (usually flies) can deliver male pollen to the female flower parts and the tree can produce fruit. Makes sense right? Well, just when you think you are getting your head around it here comes the twist: colder climates disrupt the normal flowering habits and so in places like Melbourne you get flowers in both male and female phase on the one tree at the one time. Bonus! This overlap allows partial self-fertilisation to occur. The cold delays the transition from male to female. The result is in Melbourne you can plant just one avocado tree and expect a good harvest, but plant one A and one B variety, and you will enjoy a bigger crop on both trees. Oh the romance!
Avocado trees can reach a height of five to ten metres at maturity so many suburban blocks will only have room for one. We stock mostly Hass because they are very reliable fruit-setters and have a great flavour. All avocado trees like good drainage but can suffer from drought stress due to their small root systems, so water well in the warmer months while they are establishing. So basically, love your avocado tree and it will love you back, in the form of its delicious, mysteriously-formed fruit.
If you want to get deeper into the science of avocado pollination here’s a great article: http://www.lauriemeadows.info/food_garden/fruit/Avocado_Pollination.html