Decision Time For My ‘Air-Pot Mini-Orchard’ Apple Trees

For the past few years I’ve been growing three apple trees in Air-Pots in the back garden. It started as a (not at all scientifically conducted) trial / experiment to see whether or not this method might be viable long-term, but I think phase one of the trial has now run its course.

It ought to be a feasible growing method: air-pots are widely used throughout the horticultural industry, particularly by tree nurseries, as a means of developing strong and healthy root systems on young trees, and I’ve seen several examples of quite mature specimens being grown in larger air-pots. Surely they would be an ideal container for setup for apples on dwarfing roostocks? Certainly better than the usual large, plastic plant pots with notoriously poor drainage and solid walls that force roots into becoming pot-bound.

However, after a catalogue of schoolboy errors – all of which can be firmly placed in the “if I only knew then what I know now” category – results have not been great. The trees have struggled to put on any meaningful growth[1], and they’ve always suffered from rather sparse leaf coverage, which in turn has fed back into their poor growth, due to much lower rates of photosynthesis than would have been ideal.

Fruiting has also been poor, with no apples to speak of last year or the year before. And although the ‘Herefordshire Russet’ did have a good showing this year, as did the ‘Cornish Aromatic’ (before… well, see below for what befell the ‘Cornish Aromatic’), their fruits have been distinctly small, as you can see from the picture above, even after thinning and then re-thinning them over the summer.

I’ve therefore decided that the time has now come to knock this alpha pilot on the head and re-start the process next year. Here’s where, in my naivety and over-enthusiasm, I think I went wrong, and how I’m planning to correct those errors moving forwards.

1. The Wrong Trees

First up: my process for selecting the cultivars and individual trees to grow wasn’t ideal. What can I say? Back in 2016 I visited the Grow at Brogdale offices on the way back from a holiday in Kent, on what turned out to be one of their busiest days of the year (I think it was their summer cherry festival). I then got over-excited and ended up snap-buying three trees that… well, lets just say they didn’t turn out to be all that suitable for the growing method I had in mind.

Here’s what I ended up with (from left to right in the pic above):

  1. ‘Herefordshire Russet’
  2. ‘Cornish Aromatic’
  3. ‘Blenheim Orange’

For the record, although ‘Herefordshire Russet’ and ‘Cornish Aromatic’ have seemed reasonably happy (if not ecstatic) in their air-pots, the legendarily vigorous ‘Blenheim Orange’ is definitely a poor choice for container growing[2]. It was my error: I should have been much clearer that I wanted straight, cordon-suitable, single stem trees with a few short side branches, rather than the tall, bowed, already widely-branching specimens that I eventually received.

The New Plan: I’ll be re-starting the process with cordon-suitable trees of varieties that I know aren’t too vigorous and have a natural tendency towards spur-bearing[3]. I have twenty M27 rootstocks on order for delivery early next year and I plan to graft one or two of ten or twelve different cultivars[4] and then start them all off in small air-pots. The three or four young trees that seem to be most suitable will then be transferred to larger air-pots for the longer-term trial[5].

In the meantime, the three trees from the “alpha trial” definitely won’t go to waste. The ‘Herefordshire Russet’, on M27 rootstock, will be planted out on our main allotment plot, or possibly on Plot #79 if room can be found, likewise the ‘Cornish Aromatic’. And I’m hoping to donate the ‘Blenheim Orange’ to a local community orchard.

2. The Wrong Location

In our relatively small, suburban back garden the only space we have for three air-pot grown trees is along a fence outside our back door. Whilst this means the trees are relatively sheltered, it has resulted in a couple of fairly major problems:

  1. Insufficient Light – this part of the garden receives a fair amount of sunlight first thing in the morning, and quite a bit from around 2:00 p.m. or so through to early evening. But for a good four or five hours in the day it’s in the deep shadow of the house, and then later in the summer evenings it’s shadowed by the neighbours’ large, veteran ‘Crispin’ (‘Mutsu’) apple tree, which is nicely ironic. I suspect this definitely limits the trees’ potential for photosynthesis.
  2. Easy Access for Predators – a problem I first encountered this year – it being the first year we actually had any apples on the trees – is the ease with which squirrels are able to run along the fence and grab or bite at the apples on the trees. They took most of the ‘Cornish Aromatic’ and several of the ‘Blenheim Orange’ fruits [6], before I realised what was going on.

There is, however, nowhere else in the garden to put the trees where they won’t be in even deeper shade, or within even easier reach of squirrels. Or blackbirds… or pigeons…

The New Plan: Once I’ve selected the trees for longer-term air-pot growing, I plan to relocate them to our main allotment plot. That way I can place them where they’ll receive much better exposure to light, and with any luck any predators – which, on our allotment site sometimes includes parakeets – will be distracted by the abundance of other fruit and veg produce across the site[7].

I also plan to graft and grow mostly russet varieties, if I can source enough graft material from interesting vareities / cultivars. Our ‘Herefordshire Russet’ apples have remained unattacked by squirrels, most likely because they aren’t red in colour[8] and therefore don’t show up anywhere near as well on tree-rodent radar.

3. The Wrong Care Regime

Pot-grown trees are always going to be dependent on the orchardist for the majority of their irrigation, nutrition and general care requirements. Trees will quickly exhaust the nutrient reserves in their pots and I’ve definitely noticed that the growing medium in air-pots can dry out very quickly in hot weather. The feature of air-pots that provides their unique functionality – the hole-tipped cones that make up the walls of the plastic pots encourage a strong feeder root system by ‘pruning’ the root tips as they reach the air at the end of the cones, but also provide a very fast and efficient route for both moisture evaporation from the growing medium and run-off during irrigation. In short: they leak. A lot.

And I do have to confess: life being tremendously busy as it always is, I haven’t always made enough time to monitor the condition of the trees, respond to any problems or issues as they arise[9] and generally ensure that they all have adequate water and are fed at regular intervals.

The New Plan: The answer to this one lies in the proper scheduling of appropriate irrigation and feeding schedules, after thorough research into the nutrient requirements of pot-grown trees; taking into account the appropriate nutrient balance for the varying stages of annual growth. I’ll also make sure that the growing medium is replenished on an annual basis, and apply suitable top-dressings of composted bark and/or leaf mulch to help reduce evaporation whilst providing a small amount of additional slow-release fertiliser.

In Conclusion

This was an interesting idea, but was poorly executed by someone with far more amateurish enthusiasm than useful knowledge. Hopefully I’ve accrued enough of said knowledge in the intervening years to be able to re-start and successfully carry out what I still think would be a really interesting trial into a viable long-term growing method for small but productive trees. Much better planning, preparation, setup and ongoing management will be the watch-words of my new approach.

I admit, this may turn out to be a little more difficult than anticipated if the trees are re-located to the allotment, although in warm weather I do spend a significant amount of time irrigating the plot as a whole, so the trees can easily be included in that process. And as I’m re-starting the project with newly-grafted trees that means I have a year’s breathing space to ensure that the aforementioned research is as thorough as possible and that the care plan I put in place is a manageable one.

Whatever happens, I’ll be sure to keep you posted. Or, if you would be interested in joining in by growing your own long-term air-pot container trees, please do drop me a line to let me know. I’d be more than happy to collaborate by swapping notes, ideas, and progress reports as we go.

Footnotes

Footnotes
1 Not that I was expecting them to grow too vigorously, but I was hoping for more secondary growth and thickening of the trunk and main branches than has occurred.
2 I’d have to double-check, but I think our tree was supplied on ‘standard’ MM106 rootstock, just to compound its unsuitability…
3 Which means the likes of ‘Blenheim Orange’, ‘Bramley’s Seedling’, ‘Withington Welter’ etc. are definitely out
4 I’ll definitely be grafting scions from the ‘Kidd’s Orange Red’ on Plot #79 and the ‘Tydeman’s Early Worcester’ cordon on our main allotment plot, and via friends at RHS Bridgewater (where I’ve been a weekly volunteer for a couple of years) as well as a couple of other orchards and orchardists of my acquaintance, hope to be able to source a few more interesting varieties.
5 All being well, grafts taking etc., another dozen will be planted out along a new cordon fence on our main allotment plot.
6 It took the furry-tailed rodents just over 24 hrs to reduce the ‘Cornish Aromatic’ crop from 12 apples to just 2…
7 It probably helps that our plot is fairly central, meaning there ought to be plenty of other targets for the squirrels to reach when they venture in from the surrounding trees, before they get to us…
8 I’ll just have to hope that the reasonable amount of russeting on ‘Kidd’s…’ and ‘Tydeman’s…’ will provide just enough camouflage to keep them safe.
9 Or, ideally anticipate likely problems before they arise… the pic at the top of this section shows the leaves of the ‘Blenheim Orange’ tree after a sudden hot spell in September. Overnight, around 80% of them went from green to yellow and then dropped off the tree; surely a drought-response resulting in the tree shedding excess leaf in order to reduce rates of transpiration? And equally surely a response that could have been avoided if I’d paid more attention to the weather forecast and ensured the trees were well-soaked before the hot spell hit, and ideally were well-watered during it. Instead, I was hosing down the rest of the garden and running back and forth with watering cans down on the allotment… so it goes.

2 comments

  1. Can I also point out that the Air-Pot containers are not filled properly. The compost should be right to the top and compacted as much as you can – it will not become anaerobic. The three rows of uncut cones at the top are there to make watering easier. Please watch the video on our website about assembling and filling – its at the bottom of the home page. https://air-pot.com/garden/ The enhanced root development will mean that the trees will need more nutrient and water and this will lead to faster growth.

    1. Thank you Julyan, that’s really good to know. I obviously defaulted to the ‘leave room for the water’ pot-filling method, but if the Air Pot people say they need to be filled all the way – and compacted, too? Interesting… – then that’s what I’ll do when I re-start the new trees. Much appreciated!

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