Now, if the seed companies and garden centres and all those people trying to sell you stuff are to be believed, this is the Next Big Thing.

Personally, I don’t know quite what to make of it.

On the one hand, I know people are running out of space: the good Lord knows I’ve come face to face with that particular trend while combing the south of England for a new house. Gardens are undeniably getting much, much smaller: in fact unless you’ve got a million or so to spend (or are willing to live in the lee of a motorway), large gardens don’t seem to exist anywhere within a 100-mile radius of London.

This is particularly true in cities, of course: my last city garden was in Chiswick W4 where I had what was considered even then (and I go back some way) a massive garden: it measured 40ft x 20ft including the patio.

At the same time, city folk – and not a few people who don’t live in the city – are mobilising en masse to grow their own grub. This is a fantastic and rather delightful phenomenon which I hope continues indefinitely as it’s altogether a Very Good Thing.

Only one problem. Growing grub – if you want to actually feed yourself in some form – takes room. And a lot of it. Allotments, as we all know, are more difficult to get hold of than a Lib Dem spokesman in a crisis: so you can forget that, then. That’s when those inventive folk at the commercial end of horticulture started wittering on about vertical gardening. The trouble is – it doesn’t work.

Well, that’s not quite true. I’m sure it does work if, as at Thompson & Morgan where this rather wonderful vegetable wall was photographed, you have a industrial-standard automatic irrigation system running along the top of the wall into which the exactly-measured amounts of fertiliser are being dripped.

And it probably also helps if, as here, you were only growing for a display to impress journalists rather than actually produce stuff to eat: this wall had lettuce growing alongside beans (so in real life, when it’s sunny, the lettuce bolts, and when it’s shady, the lettuce is fine but the beans sulk). And a melon, greedy plant that it is, growing in a pocket which would have allowed a rootball all of about 8″ across. No melon I know would grow at home kept constrained like that.

I don’t want to bash T&M as this was really quite a spectacularly beautiful wall and did show just what’s possible. It did however undeniably overlook the fact that the number of people growing at home who can put in the expense and effort required to give their veg growing in this way such ideal growing conditions is vanishingly small. Most people, let’s face it, just muddle along: and for these people, growing veg in pockets on the wall is surely setting yourself up for a crashing disappointment.

Growing veg in pots is fine – in fact it works, really well, and I do it all the time. But the First Law of Patio Veg Growing is that the bigger your pot, the better your veg: and in terms of volume, pockets are really, really small.

There are aspects of growing in pockets which definitely do work: shallow-rooted plants like lettuce (if kept in a shady spot and not grown alongside beans) do very well in them, as do drought-tolerant veg like kale, spring onions and chillies. Dwarf French beans don’t mind and tomatoes do sort-of OK, if you choose one of the tumbling container types, though they do look very sickly towards the end of the season and it’s hard to keep them adequately watered.

I liked the idea of dwarf peas as I haven’t tried them yet – they had ‘Twinkle’ on this wall which is a good type – but how many are you going to pick off that lot? A handful? Maybe two?

And that’s the other problem: if you’re going to grow your own at home you need to have a reward of some sort to show for it at the end of the day. A handful of peas is simply not worth the expensive compost, pockets, irrigation system and/or time, both in setting it up and looking after it.

And as for growing potatoes in compost sacks…. I went around chuntering for days after reading Sarah Raven’s article on growing potatoes in containers in last Saturday’s Telegraph Gardening. It all sounds quite sensible until you look more closely at the yields she got from each 60-litre sack.

Largest yield: 3lbs 12oz (‘Foremost’)
Smallest yield: 1lb 5oz (‘Anya’).

My Delia recipe tells me that a single shepherd’s pie, serving 4, requires 2lbs potatoes.

So, let’s see. For £4.99 (peat-free multipurpose compost) plus the cost of fertiliser – never mind water and time – we’ve barely grown enough for one meal’s worth of food. That’s about £1 per potato. Heck, even Waitrose’s best organic only costs £1.33 for 2lbs.

It’s this sort of thing that gives growing your own a bad name. Harrumph. Rant over.