Brisbane Local Food

Growing local

Having just attended a very busy two days of the Qld Garden Expo in Nambour, I should share some of the things I learnt from talks attended there, before they disappear from the memory. Peter Young of Birdwood Nurseries related that most commercial growers of fruit trees are now restricting the height of their trees to around 3 metres. This done mainly because of WPHS issues for their pickers, all fruit can now be picked from the ground. The growers have pruned the trees so that they spread out more sideways and the harvest has not been affected as much as they expected.  Where possible they have also interplanted. This has further enhanced their harvest. When the trees get their tops taken off, some of the root mass dies back. This knowledge has implications for people like me who grow some of their trees in pots. Obviously it is wise to not allow trees to get too big in pots for many reasons. One of the main worries that I was concerned about was that where I have a tree like a Dwarf Avocado getting taller, I can cut the trees back each year to control  top growth (height), but does the root growth keep on going until the plant is pot bound? I was envisaging having to take these large trees out of their pots and trimming the roots back every few years. Well now I know that I don't have to. If I prune back the top, a corresponding amount of root will die back. So In theory I don't have to repot into ever larger pots, I can control the tree size all round. This means that once the tree has attained a good size that will allow me to get a harvest size that I am happy with, I can leave the tree in that size pot.

Other info relating to growing trees in pots is that the growing mix should be around 30% sand, 60% of a good (four ticks) potting mix, and 10% coir or peat moss. The slow release fertiliser that comes in the potting mix will only provide nutrition for a few months, so you will need to top this up around 4 times a year. I  always put well rotted horse manure in with my mix, down the bottom of the pot so that the roots can grow into it. I then top up the pot with manure a few times each year, and mulch with sugar cane.

If you just use organic materials in your mix, the mix can slump too much, the sand provides some body to hold everything together.

Where a fertiliser bag states " provides food for up to 3 months" (or however long). The nutritional release is like a bell curve, The initial amount is small and gradually builds to maximum after a month and a half. By the time the three months is up the amount is back to almost zero. So to keep food up to you plants, when using the above type of fertiliser you would need to add more after a month and a half, etc. etc.

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Comment by Roger Clark on July 17, 2015 at 17:31


It's good to know that even the "experts" don't always agree on what is best for plants. There is obviously some leeway in what will work and what wont. Obviously sometimes I follow the wrong expert! Most advice allows some freedom and I believe in this collective of "non experts" called BFG, we all do pretty well in our own way. 

Comment by Elaine de Saxe on July 17, 2015 at 15:19

Any mix containing organic matter will slump. That's your friendly soil microbes doing their job munching away and giving you free fertiliser. Only way to stop that is to use all non-organic materials and use manufactured fertilisers or go to hydroponics.

Comment by Michael Hoff on July 17, 2015 at 9:19

I attended a lecture by Jerry Colby-Williams at Qld Garden Expo in Nambour last year, he uses a potting mix of 25% Coir, 25% Compost and 50 % good quality Potting Mix, plus a 400g tin of Blood & Bone and a 400g tin of Poultry Manure.  I have been using this for the last year and it works well but does slump a bit.

Comment by Lissa on July 14, 2015 at 6:29

I have two of those female tools also Roger. Know what you mean. Neither is inclined to being useful in the garden. Love em to bits. The Son Tool is known to mutiny when it comes to lugging quantities of pungent stuff like composted horse poo. That is unless another Male Tool is around in which case he likes to show off his prowess and general usefulness.

Comment by Roger Clark on July 14, 2015 at 6:18

You are very lucky having one of those tools Lissa. Very handy, but as you say, the tool may not last. I have 3 medium to small female versions, but the only one strong enough to be useful in this regard is not inclined to use in the garden!

Comment by Lissa on July 14, 2015 at 5:13

Good infor Roger, thank you.

When it comes to replenishing the soil for my Jackfruit in a pot I use the Giant Son tool. I position the tool holding the plant in the air while I madly fill the bottom of the pot with composted horse poo. I will most likely continue with this method as long as the tool is available to me. It's a fairly lazy tool, so that may not be forever.

Comment by Roger Clark on July 13, 2015 at 17:22

I repotted two blueberries today using the stated percentages, well as close as I could. I took a ph test of the sand (from my back paddock) about 5.5 (surprising), my home made compost about 5.5-6.0 and some Azalea / Roses potting mix, about 5.5-6.0 and coir soaked in seaweed rich water. I mixed this all together in a wheel barrow and then potted the plants up. So this should be a good mix for these acid loving plants. I then used pine needles as a mulch, which should maintain the acid levels. The only thing I didn't do was to test the ph level in the pots that they were in. Bugger! Oh well if they don't do well, I will give up.

Comment by Elaine de Saxe on July 13, 2015 at 15:06

Sand is so heavy for we old boilers to haul around that I never use it. Just el cheepo potting mix with plenty of coir, composted animal manures and mulch. A high organic-matter mix which does indeed need topping up from time to time. With the necessity of re-fertilising the pots (and I mean my wicking bins) topping up the mix is not such a big issue.

As for trimming roots - that's what the Bonsai people do to make the tree smaller and smaller. If the roots self-trim as it were when pruning, perhaps the result is different. I really don't know that. I keep the Figs down to about 4ft high and so far they've produced well but how it'll work in future, I just have to wait and see.

When plants are root bound and facing death, they often flower well and fruit well too. Rushing to reproduce before they die. That's how orchids are made to flower and why they don't flower in big pots. So a pot-bound plant probably will fruit but longterm it won't survive without help from us.

Comment by Florence on July 13, 2015 at 10:15

Thanks for sharing Roger! Looks like I need to add more sand and less coir, my current mix is more like 30% Coir, 10% sand, and the rest potting mix plus sometime put in mushroom compost or whatever composted material I can get...

The one problem is, sand makes the pot very heavy ~

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