I'm wanting to grow (from seed + my own grafting) an Avocado tree in an IBC container. IBC Containers are about 1m x 1m x 1m.
How practical is this, and is this space enough for an avocado tree to yield a meaningful quantity of fruit (assuming I get the grafting right and it is able to pollinate).
Relatedly, are dwarf avocados special cultivars or can any avocado be made into a dwarf by constraining its root system and pruning it ?
I think this is a bad idea. Avocados require freely draining soil, and if you're planting inside an IBC, then you're going to need most of a cubic ton of an artificial soil mix. But most of that might be wasted since the tree is shallow rooted and the main feeder roots are in the first 6 inches of soil. Trees can potentially grow 60 feet high, so you're continually going to have to prune it to keep it under 2 metres, but it's already one metre off the ground making your task harder.
When planting a dwarf avocado they suggest you start with a 60 cm pot, and repot every second year, and change the soil.
Your IBC might last 5 years more or less under NZ's high UV levels just when your tree is about to start first fruiting. And then you'll need to repot it.
If you're looking for a meaningful amount of fruit and you have to plant into containers, then maybe purchasing a number of dwarf varieties is the way to go. You'll do better with two avocado trees anyway for cross pollination, a type A and a type B.
Dwarfing is usually done by grafting the scion onto a dwarf root stock. The root stock controls the height of the tree.
I agree with Graham that this is not likely to produce the results you want if you use regular Avocado stock. There is a dwarf avocado called the Wurtz which will successfully crop when grown in a container. It gets about 3M (10') tall.
Issues will be your temperatures which are right on the edge of what it will tolerate ( -3 Deg C or 25 Deg F).
Pollination is another matter of concern. To get good fruit set you need a type of avocado that complements the Wurtz pattern. I had no idea how complicated this is.
There are two types of avocado trees,Type A (Wurtz) and Type B, defined by the time of day that the flowers are open and are available for pollination. Each flower opens as female either in the morning (Type A) or in the afternoon (Type B). It closes, then reopens on the second day as male, and then closes permanently. This pattern occurs reliably when the temperatures are ideal - above about 70 degrees day and night. When temperatures are below about 60 degrees, or if pollinators are not present when both male and female flowers are open, fruit set is poor.
So you will need some dwarf avocado in containers and a full sized version to pollinate. Protection from cold during winter and flowering is important.
Any trees in containers have an increased demand for water (ten to twenty gallons a day!) so I recommend an automated system. Regular fertilizer and top dressing are required.
Due to the avocado's tendency to shallow rooting any plants in containers should be protected from strong wind. Guying and staking may be a good idea if windy weather is anticipated.
