Be they grand or modest, all potager gardens have one thing in common. Their beds, generally but not always rectangular, are invariably surrounded or supported by something. The nature of this edging is one of the most important decisions a new gardener must make.
The square foot garden, that is in my humble opinion, a rather anaesthetised version of the classic potager, is divided into foot square, or 30cm square sections. A bed can be 90x120, 120x120 or as in my case 60x240cm. Oh woe is me, that when I designed the garden, I forgot about edgings. Allowing for the width of a wooden or brick upstand, the thickness of a fringe of herbs or the bulk of a box mini-hedge, can make the minimum size much larger.
In the beds where I have placed edging plants I allow about 15cm for the mini-hedge. But even this tiny size will overshadow the first few centimetres of soil. In a 60cm square, edged all around the actual growing space could reduce to 30cm square.
Do not reject attractive edgings because they take up space. Edgings protect against winds, distract pests and attract pollinators. They also look pretty.
The modern French potager plot is often laid out as a series of 30cm square vegetable patches. It is called the 'potager en carre'. But more often than not this rigid arrangement is softened by provision of an extra 15 or 20cm on one, or all sides to allow for an annual, perennial or herbal edging. I've drawn some example layouts for you below.
- Four 90cm wide plots with the narrowest paths between them. In my view 50cm is about as small as paths can be. My paths are 60cm wide. Here the centre strips would be nice as perennial herbs, like lavender, or annuals like marigolds. An extra strip across the back, the norther side of the garden, allows for a protective trellis of climbers or fan trained fruit trees.
- Four 120cm square sections, each with with an extra 20cm on two sides and 80cm wide path between the beds. Each bed could be edged with a contrasting vegetable or herb. Red basil and unheaded lettuces both make good edgings. Choose low growing species to avoid overshadowing.
- This is a more elaborate layout with four 120cm beds, wider paths between them and some infill pieces to east and west. The most favourable southern aspect has been filled in with another bed, 60cm deep. It is important to be able to get to the farthest corner of each bed without needing to stand on the soil, hence the setback in the centre. This would be a wonderful position for a bench. The central, circular bed might have something like a specimen standard rose in a pot, fringed below with a single vegetable cultivar.Chervil or parsley, would make a nice annual fringe, alternatively a succession of cut and come again red leaved lettuces would complement a magenta rose. Alternatively, as illustrated below, fill the urn with pollen rich flowers like Buddlea, to attract butterflies right into the heart of the garden.
My beds are 15cm high, built on top of wooden pallets that allow drainage below. The timbers are untreated softwood, 18mm thick, which for smaller beds are light enough and strong enough to sit on my rooftop. Ask me in ten years’ time whether that was the right decision. It is also quite easy to get 225mm or 300mm timber boards in DIY shops. If you are making the beds on solid ground, the extra depth of soil might be worth it, but for me the weight was the limiting factor. The wider the boards, the thicker they must be to stop bowing. In between the raised beds I have placed 60cm square timber decking. These disguise the edge of the pallets. At the time it was the architect in me that made the whole thing modular, using the 60cm squares as my module. However, now I am starting to change things around, a grid layout has proved very useful. It is quite easy to take things out, even to move an entire bed, without destroying the integrity of the whole arrangement.
There are hundreds of proprietary raised beds on the market, ranging from plastic and cotton bags, plastic clip together systems, metal struts and very solid timber systems. There are also natty little willow fences that you can use to edge the more unsightly ones. You could also use recycled boxes, Alys Fowler advises Champagne boxes and I’ve noticed some very cheap lattice boxes in Ikea, which come with a fence type slatted backing, which would be ideal, in the right location.
My plain timber beds looked a bit utilitarian before things started to grow. But it is the plants you look at not the box, especially if you edge very visible beds with trailing flowers. So I would advise not getting too carried away and not spending all your money on the bed itself.
In my garden, each bed has a Terram, horticultural lining. This matting holds the soil inside the beds, allows good drainage and stops slugs from burrowing into the soil from below. When I moved one of these beds a week or two ago, I was very pleased to see that slugs had not multiplied underneath the beds. My guess is that the Terram matting makes the underside relatively uninviting. It is slightly rough to the touch and may irritate them. If that is the case, then it was a good choice!
Each bed started out with a mix of ⅓ compost, ⅓ vermiculite and ⅓ expanded coir. As time goes by, this mix has changed. I'm not re-stocking with vermiculite. It does have a nasty habit of ending up clinging to lettuce leaves. Though it is relatively inert, I don't like to find it on the salad plate!
Every year I have buried half rotted vegetable matter where I want a hungry crop to grow, and I’ve top dressed, composted and mulched! This gradually modifies the soil. See October Soil Fertility, Slowly the thickness of soil is increasing. The original mix seemed to be perfect for leaf crops, tomatoes and potatoes, in the first years, but I didn’t have much luck with root crops like carrots, radish and celeriac at first. I think the mix might have been too nourishing. I now grow these in special locations.
The soil in rasied beds is rarely more than 30 or perhaps 45cm deep. I maintain that deep beds are not essential, unless you have difficulty in stooping to maintain them. The arguments are complex. The roots of plants fall into two categories. There are fiberous rooted species, like legumes, where the roots grow out in a maze of fine feeding fingers. These wide-rooted plants do well in containers. Tap rooted plants like carrots have a central root that may grow downwards for many feet. Tap rooted species need depth and even the shorties like radish and beet may not be happy in shallow beds. Show carrots are often grown in special rasied bins that are over a meter tall.
Roots grow in response to a search for water as they grow they amass nutrients within their structure which they release to the plant as the water is percolated upwards. In some plants the water seeking roots may be quite different to the feeding roots. in tomatoes fleshy roots may travel several feet to seek water, but a mat of fine surface roots develops around the top of the soil. This mat absorbs nutrients. If you water plants well they don't need such a large root system. (thought they might need staking.)
Nutrition seeking roots do not go deep, where soil oxygen becomes scarce. Roots make use of this oxygen to metabolise nutritients. That is why compacted soil will not produce good crops. A glance at soil profiles will reveal that the most nutritious soil is rarely 15cm deep. Even in forests that support large trees and an undercanopy, the topsoil may be less than 50cm deep.
Roots rarely grow down like an inverted branch pattern, the are much more likely to grow outwards. Thus shallow but wide raised beds allow the plant roots to fan out for nutrition and even six inches of good quality soil may be more that you will find in the wild.
The question of the northern most side of the plot is an important one. Here you can add a trellis, or other means of gaining height. This can magnificently increase the growing area, and provide wind protection from the north. Vertical planting will be the subject of a whole article later in the year (probably about the time I start to plant out my climbing courgette.) But for now the important point is not to forget to allow for the extra space that a trellis will require.
First published March 2013, Updated March 2014