Inside the polytunnel, the width and position of the beds and paths inside it is the most important piece of planning you will do. While it’s tempting to make the paths narrow, resist the urge – you’ll be spending a lot of time in the tunnel, so don’t leave yourself short of work space.
Even if you’re trying to maximise your veg-growing space (and who isn’t), don’t forget to allow plenty of room when you’re planning paths. To allow you to get through with a loaded wheelbarrow as well as room for kneeling down, paths should usually be between 50 – 75cms wide. It’s helpful if they have a clearly defined edge so that you know where the path stops and the bed begins. The boards at the sides of raised beds do this for you, but for soil-level beds a row of bricks or narrow planks will do the job.
Stepping off the path onto the beds is a bad idea, because it compacts the soil. If your path layout leaves you with awkward spots to reach (and sometimes this is unavoidable), keep a short plank to hand and lay it on the soil to use as a stepping stone when you need one. This is an old gardeners’ trick to spread your weight out, and causes far less compaction than your foot alone.
Digging the beds
Once the plan is ready, it’s time to start digging. If the ground being turned into beds has not been cultivated before, it will be rough grass and weeds. The easiest way to deal with it is simply to cut it into chunks with a spade and turn them upside-down. Over time the inverted turf rots down into compost, and this is adequate for most types of fruit and vegetables. Double-digging is exactly the same, except you put the turf to one side while you remove the soil to a further spade’s depth, so that the grass goes right at the bottom.
Whichever method you use, digging will clearly define the bed area. Once that’s done, it’s time to lay weed-proof path membrane. This can be tucked down into the edge of the beds as shown.
If you’re creating raised beds you’ll need boards for the sides, and stakes to hold them in place. Visit your local building supply merchant and check for a skip of unwanted off-cuts of wood. If you’re lucky you’ll find some lengths of 25 x 50mm timber – but make sure they’re untreated. If you can’t find any in a skip, they’re usually cheap enough to buy. Cut them into at least 50cm lengths (assume roughly 25cms below the ground at least that much above it) and trim one end to a point. When hammered firmly into the ground, these will hold the sides securely.
These make ideal sides for raised beds. Call your local scaffolding company and ask if they have any damaged planks for sale. They’re not allowed to use these on-site, and usually have a few available. Tell them what they’re for, and they’ll probably know exactly what sort of thing you want. Gardeners have probably been calling them for years.
Remove the protective brackets from the ends of the scaffolding planks, cut them to size, and lay them flat alongside their final position. Scaffolding planks are hefty pieces of wood, and if you’re cutting them by hand you won’t need to go to the gym for a day or two. A chainsaw is much faster and easier (after all, the digging was strenuous enough, wasn’t it?), but don’t use one unless you know how to handle it. Always wear ear protectors, goggles and gloves, and don’t be tempted to use a chainsaw inside the tunnel – not only could flying chips damage the cover, but the noise is unbearable.
Whether or not you decided on raised beds, spreading plants such as squash will flop all over the paths unless you plant them far enough away from the edges. Being somewhat brittle it’s difficult to point them where you want them to go. Other plants may surprise you: bush beans, for example, might stay fairly small in an outside bed…but in a polytunnel the climate will be so much more to their liking that they may grow better and faster – so be prepared for plants to be considerably bigger than you’re used to.