Small-space gardening is becoming increasingly popular as outdoor spaces and gardens get progressively smaller in urban areas. There are many ways to maximise the use of limited available space, and one of the best ways is vertical gardening, growing upwards rather than outwards!
Gardeners are very resourceful, and in the gardening world there are many techniques which have been developed to take advantage of vertical spaces, such as espaliered trees grown flat against walls, even more compact columnar ‘cordon’ tree forms, and methods which rely on structures such as trellises and arbours.
Some of the best vertical gardening solutions can be so deceptively simple that it’s often overlooked! One of the least appreciated ways of growing edible climbers is over an arch, mainly because people don’t realize how much growing space is available on a relatively small archway.
How Much Growing Space Can Arches Provide?
An arch at first glances would appear to offer very little growing space. How much growing area can a small 1m (3’) wide x 2.5m (8’) high arch, a little taller than a house doorway, actually provide? If we do the math, we might be in for a bit of a shock.
Most people ignored maths at school, and glossed over geometry. Where will I ever use this stuff? Well, life is full of surprises…
To calculate the total length of an arch, we can simply use a tape measure, but when was the last time anyone did that? Arches are often dismissed as being small and insignificant, and without first considering the value of arches, there is no inclination to seek them out for measurement!
Calculations are useful for design purposes, we can use them to work out the size of an arch required to support a certain length of edible vine such as a grape of berry, or we can determine how much growing space an arch of a given size can provide.
The short answer:
The formula for calculating the total length of an arch = (2 x length of vertical side sections) + (3.14 x 0.5 x width of arch)
The diagram below shows how an arch consists of two main sections, the pair of vertical sections at the sides, and the curved section at the top, and how their lengths are used in the calculation.
If we use the earlier example of a small 1m (3’) wide x 2.5m (8’) high arch and put these figures into the formula:
- total length of an arch = (2 x length of vertical side sections) + (3.14 x 0.5 x width of arch)
- total length of arch = (2 x 2m) + (3.14 x 0.5 x 0.5m)
- total length of arch = (4m) + (1.57m) = 5.57m
What this tells us is that an arch not much larger than a house doorway can support a vine over 5m long, and it only occupies a very small area on the ground where the vine is planted, which can be as little as 50cm x 50cm (around 20” x 20”). That’s a very efficient use of space!
The long (and possibly unnecessary) mathematical explanation:
How was the formula above derived? This is for those curious about the maths, otherwise just skip this section!
An arch consists of two main sections, the vertical sections at the sides and the curved section at the top. To calculate the total length of growing space of a garden arch, we need to add the length of the vertical sections at the sides to the length of the curved semicircular top section.
- The length of the vertical side sections are known.
- The length of the curved portion can be calculated using the formula for the circumference of a circle (the length around a circle).
To explain how the formula given earlier was derived mathematically:
- For a whole circle, the length of the circumference: C = 2π x r , where π = 22/7 or approx. 3.14, and r is the circle radius (half the width)
- For a half circle, we halve the formula: length = 2π x r x 1/2 = π x r = 3.14 x r
- Since the radius is half the width of the arch, the simplified formula therefore can be expressed as:
total length of an arch = (2 x length of vertical side sections) + (3.14 x 0.5 x width of arch)
Permaculture Small Space Intensive Gardening Using Arches
The Permaculture design principle known as the ‘Edge Effect’ is concerned with the use of edge and natural patterns for best effect. In Nature we see extensive use of folding to maximise functional area in a small space. The human intestines, both in terms of their outer form and the structure of their internal surfaces for the absorption of nutrients, are both a perfect example of this.
Now consider how long a 5m (15’) long vine really is, that’s quite a decent productive length of vine by anyone’s books, and a trellis this long to support it would occupy a considerable amount of space. If we do what Nature does and fold the support structure in half into the shape of an arch, the growing space ends up concentrated into a much smaller area no bigger than a doorway.
If the arch is situated to span across a path, it converts unused walkway into growing space without obstructing access. A free standing arch in a garden multiplies space, as the the area underneath the arch can also be planted up, creating a double-level planting.
The photograph at the start of this article is of a loganberry arch in my backyard Permaculture food forest garden, which has proven to be extremely productive. This arch sits over a path, one side sits in the garden, the other beside the back fence. The arch is quite narrow, only around 30cm (1’) wide, and I train around 6-8 canes over it, and allow them to grow right over the arch, where they reach the fence. I then run the canes along the fence for an extra metre or two.
Considering that this loganberry arch has 6-8 fruiting canes, each around 5-7m long, is it any surprise that it’s extremely productive? The loganberry only occupies a very small area in the actual garden bed, the footprint is minimal, approximately 30cm x 60cm, around two square feet, yet it supports a total of 30m-56m (98’-183’) of productive canes.
The same loganberry vine is pictured below, during harvesting time. It’s no exaggeration that people have picked enough berries to fill bags and the plant looked untouched due to the very heavy cropping. Daily harvesting becomes necessary with this much production. To protect the berries from birds, it’s easy to toss a length on 2mm insect exclusion netting over the arch, the fine mesh doesn’t get tangled on the brambleberry thorns and also provides 20% shade for the berries during hot, windy weather, preventing them from over-ripening and burning.
Garden Arch Construction
My loganberry arch was just a cheap pre-fabricated unit from a garden store which you assemble, and was given to me by a friend who didn’t want it. It lasted around 8 years, which is not too bad. Proper commercial garden arches are usually constructed of more durable materials and will last forever. They come either as a single structure or as two pieces that are fastened together.
It’s possible to build your own arches from a variety of construction materials. A popular construction method is to a fasten rebar mesh sheet bent into an upside-down U-shape to the ground with steel posts. The mesh sheet is tied to the posts with heavy galvanised wire, or you can use U-bolts, which are used to fasten posts together.
If rebar sheets are not large enough for an arch, or can’t bend enough, two sheets can be used, one for each side, and fastened to each other at one end with some overlap using U-bolts.
The picture below is an arch at a community garden constructed with rebar mesh (which is used to reinforce concrete slabs) held in place using star pickets or droppers.
I often get questions about what a star picket is, so I’ve included a picture of one below. They’re very sturdy steel fencing posts that are also called Y-posts of droppers, one end is flat, the other is pointed, with holes along one edge to tie wire through. Any sturdy, long-lasting post can be used, and I believe the US equivalent is a T-post which is used for fencing.
A rebar mesh sheet can also be fastened vertically to create a support wall for brambleberries to climb up, and that’s what was done at the same community garden, as pictured below.
Small Arches for Extra Growing Space Over Garden Beds
For extra growing space over raised garden beds, it’s possible to construct small arches for running climbing vegetables over.
A 1.6m long reinforcing mesh arch will span a 1m wide bed, and sit only 50cm high. That’s a lot of additional growing space for such a small structure.
Arches are a simple way to increase vertical growing space, they work very well for all brambleberries (loganberries, boysenberries, blackberries, etc) and can also be used for grapevines, kiwiberries, indeterminate (vining) tomatoes, climbing beans and peas and many other vigorous edible plants which require supports to climb on. A gardener is only limited by their creativity!