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Avocado trees only flower once a year. So when they flower and they usually have a lot of flowers, you want them to set fruit. As has been previously discussed they have an unusual method of pollinisation. The flowers are both male and female, but at different times. Type A trees first open as females with a long central stigma standing erect and the male stamens which have the necessary pollen trapped underneath them lying flat. The flower then closes and when it reopens it does so as a male with the stamens now standing up to release their pollen. Unfortunately the stigma is now usually unreceptive to this pollen and has in most cases withered. To effect pollination it seems that some overlap of these happenings must occur, (if on the same tree), or if other type A trees are around. Type B trees, have the same process, but in the reverse order. On top of this, not all avos flower (or overlap flowering) at the same time. European honey bees seem to be the main pollinators. Unfortunately the nectar and pollen produced by Avos are not very attractive to bees. So if there are other sources around they will visit these instead. Another complicating factor is that if the night time temperature is too cold the flowers will not perform as they should. I.E. if night time temps are around 10 degrees this will adversely affect the chances of pollination. So here I am hoping like mad that everything will be good for pollination, but, so far I have not seen 1 honeybee in my garden this pollinating season, not near the avos, not near the nasturtiums, basil, lavender, daises, etc. etc. Are they all dead, or have they deserted me in my hour (read many days), of need? There are also no native bees around. I have always had plenty of both types around, but just not now! I have seen ants and small flies on the avo flowers, but not in any numbers, so I doubt very much whether there will be any fruit forming this year. The cooler night time temps are also conspiring against good pollination, so not a lot is going right just now. I thought that I may be able to hand pollinate, but the literature does not deem this very successful. It seems that a lot of other people have not had huge success with trees setting fruit either, am I right in this?  Or am I just wallowing in self pity? Man up Clark!!

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Comment by Lissa on October 27, 2015 at 17:40

Sorry Elaine - I meant multi graft. Not just grafted.

Comment by Lissa on October 27, 2015 at 17:30

Wish I had bought one of both sorts at the time now and planted them in the one place.

Comment by Elaine de Saxe on October 27, 2015 at 11:58

Interesting! Thank you for the research, Roger. You've got nothing to lose! The common rootstock when I was involved in selling them in a Nursery, was Guatemalan. I know nothing about it except that a lot of buyers asked about the rootstock. I am assuming that it is more suited to Brisbane conditions whatever they may be.

The observations in the American article are quite apt; thinking about the growth habit of the individual plants. Sensible.

Probably the simplest solution is 2 plants, 1 hole that way you get the right rootstock and the growth habit of the individual plants is not so important.

Comment by Roger Clark on October 27, 2015 at 8:01

Upon investigation, yes people are grafting Type A to type b or vice versa. The Sub Tropical Fruit website advises people to plant two or more tree types in the one hole. 

Here are two articles about grafting Avos.

American

I assume you are asking, if we know of anyone who is grafting A to B and vise versa? If that is what you are asking, then yes, I think many, if not most of those who graft, do it. Like many plants, often a particular root stock may be better for your soil or climate. For many of us, Mexican Root Stock is root stock of choice here in Central/Northern CA. Commercially, Duke and etc Mexican rootstock has been used in Southern CA over the years.
The only thing I take into consideration in multi grafting Avocados is matching variety for aggressiveness and growth form; Some are spreading, some columnar and a less are spreading, and a very few are dwarf or very spreading, with drooping growth, to various degrees. One more consideration, in colder areas, you can graft to put a harder protective variety on top, and a slightly more cold sensitive ones below it, if you just need a little more protection.
Mexican strain wood, does seem to take best on Mexican wood, but grafting Guatemalan on Mexican is just a bit more shaky. In this line of thought, I find that some Guatemalan and Guatemalan X Mexican take well with no apparent resistance or difficulty, but some small percent of Guatemalan on Mexican does.
I have even encountered a slight problem of Duke, a Mexican strain, on Mexican Root Stock, but the problem seems to be more about needing better sap flow, to and no high heat, to take well.
Over all, avocado plants don't seem to have a lot of intolerance issues between the 3 different strains, an no real intolerance issues over whether the flower type is A or B.

 

ABC Australia

To get a good crop of avocados, (or any fruit!) there are a few things to consider - soil, space and sex.
The sex life of avocados is fascinating! Avocado flowers are botanically 'bisexual' or 'perfect' - as they carry both male and female reproductive organs. However, different avocado varieties are classified as A- or B- flower types.
Each type has flowers that open twice over a two-day period - the first day as a female and the second day as a male.
Type A avocado flowers are ready to be pollinated in the morning, but any blossoms flowering in the afternoon are releasing their pollen.
Type B, therefore, release pollen in the morning and are ready for fertilising in the afternoon.
This means the crawling and flying insects trying to harvest the pollen don't always get to their female counterparts to fertilise the fruit. Luckily, the trees usually flower for up to a month!
In alphabetical order, the most common varieties in Australia are:
Type A - Gwen, Hass, Lamb Hass, Pinkerton, Reed, Rincon, Secondo and Wurtz.
Type B - Bacon, Edranol, Fuerte, Llanos Hass, Ryan, Sharwil, Shepard and Zutano.
Of these, Edranol, Hazzard, Shepard and Walden do best in the north; Pinkerton, Rincon and Wurtz are better choices for temperate zones; and Bacon remains the best cold-weather avocado, although Zutano will also survive.
You can get fruit with just one type of avocado, although multiple trees help. But for a cracker crop at your place, you can try to squeeze in a plant from the B side or just graft a branch of a B type onto your tree!
However, even if your avocado flowers don't get pollinated, sometimes trees can produce tiny 'cocktail' avocados.

There are obviously also lots of websites with explanations on how to graft. As I have a couple of rootstock (grown from good avos that I've bought, eaten, and planted seed from, I will give this a go. What have I got to lose?

Comment by Elaine de Saxe on October 27, 2015 at 6:54

All true-to-type Avos are grafted. Seedling offer variety but in a commercial situation, seedlings would not be viable.

I am talking about a double-graft: 2 compatible varieties to ensure pollination without having to grow 2 trees. That is what I have not seen. They may be around though, who knows what has happened in the nursery world.

Comment by Lissa on October 27, 2015 at 5:47

I mentioned earlier, my neighbours Dad reckons he has seen grafted Avo trees around (he mentioned the Caboolture Mkts) and intends buying one eventually. Hopefully he will show it to me if he does.

Comment by Elaine de Saxe on October 26, 2015 at 21:00

In the commercial situation, double-grafts would not be appealing. Or would not have any real use. They perhaps interplant compatible trees - I've never looked into this; it makes sense to me.

There's division of opinion in the nursery industry about the viability of double grafts anyway. Some vehemently opposed: e.g. in Kiwi fruit, so easily can you cut off the male graft so you're left with the female only and no fruit. Kiwi fruit are the only plants I know about first hand with double-grafts. For the home gardener, even 1 Kiwi fruit vine is more than enough, having to provide trellis space for 2 just to get pollination is more than most yards can stand. Mine included.

The Cherries that some of us bought recently are double grafts. Both grafts are of equal size and arranged in a Y so there is no doubt that the tree is in two parts. Unlikely to cut one off if it's the same size.

Although I've not heard of an A with a B graft (and vice versa) at the moment, I can see how it would be useful when space is limited. I'm interested to know how you go, Roger.

Comment by Roger Clark on October 26, 2015 at 17:03

I will explore the idea of grafting. I can't believe that the industry hasn't tried this, but maybe the production isn't there so they are not interested. For home gardeners, we want a few fruit each year not bucket fulls. I guess that the Sub- Tropical Fruit Tree organisation would be a good place to start. I'll also do some research on the web. Thanks Elaine. Florence, yes I would really like to find someone who has type B trees that flower at the same time as my type A's, somewhere secure where I could leave the trees for a few weeks at the appropriate time of the year. One problem is that the bees need to do their work and I don't know how you guarantee that they will attend your trees. Apparently the nectar and pollen on avo's is not as attractive to them as a lot of other tree flowers, so I could leave my trees in an ideal spot and still not get good pollination. It's certainly worth a try though. If only I lived on a block with good soil 5 metres deep!!! It's interesting to me that of the flowers which received pollination on my trees there are two pairs of avos developing in close proximity. I think this confirms that the pollination was performed by ants, with their lack of mobility in comparison the bees.

Comment by Florence on October 26, 2015 at 9:57

I think it would be a very welcome pot if you can find someone with an opposing type avocado tree needing pollination!

Comment by Florence on October 26, 2015 at 9:34

re: Roger moving your potting Avos around ~ I have seen a lot of avocado trees on many not-yet-developed acreages in Rochedale... I don't know how close the trees have to be to each other to get pollination, but maybe check with Rochedale community garden about fostering your tree during flowering? Just an idea...

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