For the first time in my adult life I have a greenhouse and some garden space. When we moved into our current house, it had been rented out for over ten years and the occupants had, it appears, little interest in gardening so the back garden was overgrown and contained a dilapidated shed and greenhouse. To be honest, I was in favour of demolishing the latter as it was in a hell of a state and was also, I thought, too big for the garden – my plan was to replace it with a smaller one.

My wife, however, persuaded me to give it a go so I’ve recently replaced all the glass with polycarbonate panels (I recommend Nick Gray for these if you’re in the UK). I then replaced a few more panels after they blew out during the recent record storms. Ahem. Having done this, I am now delighted to have a good sized greenhouse as I’m going to fill it chocablock with plants this summer.

Outside growing space, on the other hand, is a little limited – my garden is small with a capital S. So I’m keen to maximise the space available and have been investigating Square Metre Gardening which is the Anglicised version of the American Square Foot Gardening popularised by Mel Bartholomew.  How can they be the same when a metre is three feet? Read on.

SMG, in a nutshell, is based on a box made of boards one metre on each side. These boards should be 15cm high and I’ve found gravel boards absolutely ideal. This box is sealed underneath with weed suppressing fabric before being placed in position. It’s then filled with a mix made up of 1/3 moss peat, 1/3 peat-free compost and 1/3 coarse vermiculite. This latter ingredient is the most expensive and hardest to get – you can obtain it in the UK in 100 litre bags by searching on ebay. Just make sure you get the horticultural stuff in the coarse size if you possibly can.

Once the box is filled, thin battens are then placed over it at 33cm intervals to make a 3×3 grid – each of them roughly one foot square (hence the Amercian name). Each of these is treated as a separate growing zone and, in theory at least, is much more efficient than the traditional planting in rows.

In my case, the prime location I wanted to use wasn’t conveniently square in shape – it’s actually 1.8m (6ft) by 60cm (2ft) which means I ended up with 12 growing spaces in this first box. The box cost around £40 in total to build and fill. Whilst this may sound expensive, bear in mind that, according to Mel, you will never have to refill it again. Gone are my annual trips to the tip with containers full of dead compost.

The vermiculite is the key to this – its structure soaks up water, loosens the soil and slowly leaches minerals for the plants to feed on. The only topping up required is a single trowel of compost each time you clear a square. It should be possible to grow up to three crops per square during the year so that’s 36 in total for my one box.

How much you can grow in a box depends on the size of the plant and therefore how much space it needs. As a guide, a large cabbage or brussels sprout plant would need a square to itself whereas you could get 16 carrots, four lettuces or 9 leeks in the same space. Initially, I’m going to try broad beans and peas (4 per square – both compact varieties) along with various salad leaves.

I’m open-minded about this technique and want to give it the best possible chance because if it is viable, it’ll make my garden much more enjoyable and productive. I’ll set up a second box inside the greenhouse to maximise growing space in there and see how it compares with the traditional growbag method of growing tomatoes and cucumbers.

For now, however, since it’s still late winter, my bed is under a thick polythene sheet to give it a chance to warm up with the first planting likely to take place towards the end of March (with protection).