Gareth Carter: Like avocado? Which variety - there are at least eight

One of the most popular fruit trees at the moment is the Avocado. Photo / Supplied

One of the most popular fruit trees at the moment is the avocado. They have been recognised for their health benefits as well as a wide range of meal and snack options.

The reporting of health benefits in the media too has driven avocado popularity. They are rich in mono-unsaturated oil, proteins, vitamins A and B, while being low in cholesterol and sugar and contain a large amount of minerals.

Now is the best time of year to plant an avocado tree in Whanganui. Planting now gives the maximum time to get established before next winter.

Correct site selection is the biggest influencer of the success or failure when growing avocado trees.

They grow best in a warm situation with fertile, well-drained soil in full sun and need protection from both strong winds and frost while the plants are young. Once they are established the trees can withstand frost to -2C or -3C.

Avocado trees need a good sized area to grow. If left to their own devices they will eventually (after about 15-20 years) grow to a tree of about 10-12 metres high and 4-6 metres wide.

For those who are keen, avocado trees grow easily from seed but the downfall is they will take up to 10 years to fruit. Trees that are grafted will produce fruit after about four years and after seven years should be producing 200 or more avocados annually.

Many homes do not have a spot large enough to have a tree of this size but by pruning each year a much smaller tree can be maintained.

Intensive planting and pruning is now being practised by new commercial plantings where traditional tree spacings of 10 metres apart is now being halved to about 5 metres apart. Skilled pruning is undertaken to keep trees maintained at 3-4 metres high, while not removing the tree's ability to fruit.

BBQ Prawn and Avocado Salad with lime aioli. Photo / File

This means fruit production is far closer to the ground, reducing the labour input needed at the time of harvest. The high labour input to extract fruit from tall trees is one of the contributing factors to the high cost of avocado fruit relative to other fruits.

Many people know the avocado variety Hass and to a lesser extent Reed which are sold widely throughout NZ.

There are other varieties that should also be considered for the home garden. By planting several different varieties you will not only increase the flower pollination with better fruit set, but you will also have fruit throughout many months of the year as the varieties ripen at different times.

The varieties

Hass: NZ's favourite avocado, crocodile skinned tasty fruit, heavy cropper. Fruit mature from September to March, A type flowering pattern. Cross pollinated by Fuerte or Bacon.

Reed: Large cannon ball fruit, heavy cropper and very nutty flesh. Fruit mature from February to June, A type flowering pattern. Cross pollinated by Hashimoto, Fuerte and Bacon.

Fuerte: Very vigorous green skin avocado with some cold tolerance. Fruit mature from September to December, B type flowering pattern. Cross pollinated by Hass or Reed.

Bacon: A smooth skinned green avocado, with fruit maturing July to September, B type flowering pattern. Cross pollinated by Hass or Reed.

Hashimoto: Very vigorous green skin avocado with some cold tolerance. Fruit mature June and July, B type flowering pattern. Cross pollinated by Hass or Reed.

Zutano: More cold hardy than Hass and the earliest to fruit, ripening in July and August. Fruit has a fibrous texture with a higher water content and a lower fat/oil content. Yields well with thin skinned pear shaped fruit resembling Fuerte. B type flowering pattern.

Ettinger: Plentiful crops of smooth skin, pear shaped fruit. Lime green flesh has a buttery texture and a nutty taste. Fruit matures from August to October. B type flowering pattern.

Sharwil: Creamy with a mild rich flavour, not as nutty as Hass. Oval shaped fruit similar to Fuerte, the skin is hard. A major commercial variety in Hawaii due to its high quality and exceptional flavour and a smaller stone than other varieties. It fruits for a long time starting before Hass about August and overlaps with Reed into February. B type flowering pattern.

Pollination

Avocado trees have an interesting arrangement with their flowering. Avocado trees have been classified into A type and B type tree varieties. The trees have both male and female flowers on the tree.

A type flowering pattern (Hass and Reed): The female opens in the morning the first day for two to three hours and then closes. The male flower opens in the afternoon of the second day for two to three hours then closes. Hence cross pollination of two varieties helps in the warmer climates. In the cooler climates opening and closing of the flower tends to overlap, therefore making them more self-fertile. Cross pollination should be from a B type flowering variety such as Hashimoto, Bacon, Ettinger, Sharwil, Zutano or Fuerte.

B type flowering pattern (Bacon, Ettinger, Sharwil, Zutano, Fuerte and Hashimoto); The female part opens in the afternoon on the first day for two to three hours then closes. The male part opens the morning of the second day. Hence cross pollination of two varieties helps in the warmer climates. In the cooler climates opening and closing of the flower tends to overlap, therefore making them more self-fertile. Cross pollination using A type flowering variety - Hass or Reed.

During cooler weather the flowering can be delayed and quite erratic. This can mean the opening and closing of the male and female flowering can overlap, increasing rates of self pollination. When the temperatures are warm and reach 21C or above the flowering becomes much more regular.

So to summarise, all varieties are somewhat self fertile but the weather conditions will make a significant part to the amount of fruit set. If you have issues with fruit setting then planting a mixture of both A and B flowering types will increase the pollination.

There are good range of avocado trees available at the moment, why not treat yourself or give one as a Christmas present!

•Gareth Carter is general manager of Springvale Garden Centre.