The cage doesn't employ the fairly thick and heavy tubing of the traditional cage. This is an advantage, I think. There's a saving in cost and material, and a saving in material imposes less of a pressure on resources. A cage doesn't have to withstand great forces. It doesn't have to withstand great wind forces. Obviously, even gale-force winds can't blow the netting away. It doesn't have to bear heavy loads, except for snow. A lightweight structure is perfectly capable of doing the job, and a heavy, solid structure would be excessive. A building which uses slender, graceful columns or pillars rather than very thick ones to bear a load is in no danger of collapsing - it's using a sophisticated design to carry the load rather than a crude design.
I tend to construct large cages and generally use netting of 6m x 4m dimensions. Netting of smaller dimensions can be used but whatever the length, the width has to be adequate - 2m is generally not sufficient.
The cage can be constructed perfectly easily, simply by pushing the ends of the support into the ground and using tent pegs to secure the netting, 2 at each end. Alternatively, small sections of bamboo can be used. With the two ends of the netting secure, work down each side, securing the netting to the ground at intervals. Again, tent pegs or small sections of bamboo can be used. These need not be visible later.
Two flexible supports of the same height or different heights can be used.The two supports can overlap or they can be placed further apart so they are no longer overlapping. The possibility of using single supports or two supports at varying distances apart gives the system great flexibility - very different lengths can be covered. Different widths can be covered too. If the same netting is used but the supports are lower, then obviously the netting can be brought out further at the sides. A second further flexible support can be used to make a cage of greater width, as in this image:
Whether tent pegs or small pieces of bamboo are used, the method of securing the netting is the same, if moveable boards are used to surround the bed. (See my page on boards for the system which I use.) Before the netting has been secured, it will be hanging down in front of the board, near to you. Lift the board slightly, push the netting underneath the board so that the netting is now on the other side of the board. Push down a tent peg or piece of bamboo on the inside of the board so that it goes through the netting. The netting is now secure at this point. Go on to the next securing point. Only a few are needed for the entire length of netting. When you've finished one side of the cage, push the board back down. The board secures the netting as well as the pegs or bamboo. In fact, when a board is used, the netting can be secured without using any pegs or bamboo at all. If moveable boards aren't used, then simply peg the netting into the ground. (The cage in the top photograph is secured without the use of boards.)
One disadvantage of the system has to be admitted, but in my experience it's not at all an important disadvantage. There are metal connections in the support. After a time, these will corrode to some extent so that it's difficult or impossible to separate the sections of the support. I store the support as a single long section, without taking it apart when it's not in use.
These cages can be used for protecting fruit and brassicas such as cabbage, purple sprouting broccoli, oriental vegetables and other crops from such pests as pigeons and other birds, and cabbage white butterflies (if fine netting is used.)
The horizontal wires of the system not clearly visible here. The raspberry plants are young and have not yet grown as far as the lowest wire.
I still use a conventional post system for supporting raspberry crops, set up many years ago, but when I had to replace two old posts in one row of runner bean plants, I gave thought to the disadvantages of the post system, including the time it would take to anchor the posts solidly in the earth, and designed a system using curved supports, the supports used to construct curved cages. This system has many advantages, discussed below.
This is the support, with horizontal wires for tying the raspberry canes.
Shapes with different curvature are easy to make, as in the case of protection cages which use these flexible supports.
The curved support is put in place. The ends are simply pushed into the soil - there's none of the work involved in setting posts in the soil, whatever method is used. Two wires are attached to the flexible support at about 80cm and 110 cm from the soil. A tall support can be used, with a third wire 170cm from the soil (not shown here.) Alternatively, using a lower curved support, the raspberry canes are attached to the curved support itself when they have grown to this height, the system shown above. The system of curved supports is flexible, and can be used for rows of any length. For long rows, intersecting supports are used.
I've devised a simple method of fixing which adds effectively nothing at all, or virtually nothing, to the cost of the system. The curved support is smooth but this method of fixing prevents any slipping of the wire on the support. The tension of the flexible support gives tension to the wires, without the need for straining bolts.
This is a lightweight system but with more than enough strength to support raspberry canes. Much of the support comes from the stems of the plants, after all. They only need help.
The simple system shown in the photograph at the beginning of this section is suitable for fairly sheltered locations, but a second support can be added, with greater curvature than the main support and of smaller diameter, at right angles to the main support. It prevents lateral movement of the main support in strong winds. (The system will withstand gale-force winds - but not hurricanes.) In a site with a little more space, a system with two identical supports can be used. Looking at the supports from above, the upper diagram here shows a main support with a thinner subsidiary support. The lower diagram shows two equal supports, giving four branches for support of raspberry crops.
If protection of the raspberry canes is considered essential, then a second, longer curved support is added, with netting, and the raspberry support is within a curved cage,
In the conventional system of supporting raspberry canes, which uses posts, the erection of the posts is the most laborious stage. Use of a concrete mixture such as 'Postcrete' involves transportation of heavy material, a spiked support such as 'Metpost' has to be hammered into the soil and both methods need care if the post isn't to be too far from vertical. If straining bolts are used, then holes have to be drilled in the posts, of course, and the bolts add to the cost of the system. The productive life of raspberry canes is far longer than that of strawberries, about ten years, but time passes ... This system can be dismantled and erected in a new area in a matter of minutes. Dismantling the conventional system is much more difficult, involving removal of the the posts and getting the spiked support or the concrete out of the ground.
I use the cage system described above for protection of brassicas - essential on my allotments - and for protection of redcurrant and whitecurrant bushes. I haven't found it necessary to protect the raspberry crop, or the strawberry crop, for that matter, but other people's experience may be very different. Dr D G Hessayon writes of soft fruit, in 'The Fruit Expert,'
'Raspberries and strawberries are the types most at risk. Chemical sprays are of little use [the author has a great fondness for chemical sprays, not to be imitated] and mechanical bird scarers are of limited value. The only satisfactory solution is to erect a bird cage. For strawberries and low-growing bushes and canes a temporary cage will do, but for standard-sized bushes and canes a walk in cage is a better idea.'
Information about his 'temporary cage' is given above. My system which uses curved supports is vastly superior.
For raspberry crops, not a low-growing bush, of course, I give an alternative to the walk-in cage, one which is far more cost-effective.
In 'traditional' systems of supporting and protecting raspberry plants, support is separated from protection. To support the plants, leaving aside the single post system, which is inadequate for more than a few plants, either the post-and-wire system or the double fence system is used. For the post-and-wire system, the uprights at the ends of each row are typically about 2m high, for the double fence system the uprights are a little lower. If it's decided that it's necessary to protect the crop against the extreme damage that birds can do then by far the best solution is to erect a cage to protect the crop. So, a large cage, with its own supports, is either bought or constructed. The cage consists of a framework made of horizontal and vertical members with netting attached.
I still use a conventional post system for supporting raspberry crops, set up many years ago, but when I had to replace two old posts in one row of runner bean plants, I gave thought to the disadvantages of the post system, including the time it would take to anchor the posts solidly i the earth, and found that it was possible to replace it with a system using a curved support. This has many advantages.
If the conventional post system is used and protection of the crop is found to be essential, the support system is integrated with protection. There's no reason to erect a supporting system for the canes and then to erect a second, independent supporting system for the netting which protects the raspberry canes. Fruit cages are expensive, and a significant part of the cost comes from the supports. This is unnecessary duplication.
The vertical posts at the ends of each row in my system are higher than the vertical posts generally used in the traditional systems. They are about 2.5m high and have at the top short horizontal members about 1 metre long, like the short horizontal members of the double fence system. This is because attachment of the galvanized wires to which the canes are tied or which support the canes isn't their only function. These posts are also used for attachment at a higher level of two galvanized wires, running the length of each row, over which the netting is draped. These galvanized wires, like the lower wires, are secured by straining bolts. The netting is tied to the wires at intervals with small loops. The edges of the netting at ground level are secured with tent pegs. The whole system represents a very big saving in time and money.
It takes quite a time for runner beans to reach this stage (the photograph was taken in one of my allotments a few years ago.) Whilst the seeds are germinating in the soil or beginning their climb towards the top of the supports, these supports are exposed. Like many other people, I use garden canes. People who can use rustic, gnarled supports of character need not worry about precision, but a degree of precision is desirable in constructing a support made up of canes. Otherwise, the supporting structure won't have the irregular charm of a rustic construction but will seem simply ugly. Constructing a support isn't craftsmanship, but it shouldn't be too casual and careless.
Fortunately, a degree of precision is very easy in this case. By using a suitable technique, the job can be carried out very quickly. I favour spires, that is, pyramidal structures, often called wigwams. To construct each spire (or wigwam) only takes about 5 minutes. The same principles can be used to construct other shapes.
This is the technique I use. Decide on the area to be used for a group of support-spires. Each support spire is 80 cm long by 80 cm wide. If the spires are to occupy a bed, decide how many spires can be fitted in, allowing some space between the spires, of course. There are five canes on each of the four sides, with 20 cm between any two canes.
Lay a tape-measure on the ground - it acts as a straight edge as well as a measuring device - and with a dibber make holes at 0cm, 20 cm, 40 cm, 60 cm and 80 cm. Make holes on the other three sides. If a dibber isn't available, a suitable stick can be used. All this can be done very rapidly. The holes made by the dibber will mark the positions of the canes but also make it easier to push the canes into the soil. Simply push the canes into the holes made by the dibber, tilting the canes towards the centre of the structure, and tie the canes towards the top with two loops of twine (just in case one loop breaks.) The procedure is, then, simply this: mark out the positions with the dibber, using a tape measure, push in the canes, tie the canes.
The result. Some minor adjustments could be made to improve appearance - by retying the twine, for example - but the structures already have harmonious presence.
Below, in the foreground, a structure for supporting climbing peas (variety 'Alderman')
(The curved, corrugated iron structure visible on the right is an air-raid shelter from the Second World War (an 'Anderson shelter.')
This star will support a fig tree, planted not long ago in the container visible in both photographs - the container is small, to restrict root growth. The structure can be used to support many other plants. It's intended to be more than functional, to have visual interest not just in the growing season but throughout the year. When the fig tree, which is deciduous, loses its leaves, the structure adds visual interest to the wall. In construction, it's not as simple as it seems in the upper photograph. The spokes are made up of double pieces with a gap between them. This tensions the pieces, increasing their strength, and also increases the visual interest. A front view is of a wheel without a rim. A side view is of something more like a piece of contemporary sculpture.
The structure is a better way of supporting a fig plant and many other plants than the use of wires, which have to be tensioned. Wires contract in cold weather and expand in warm weather. It's difficult to avoid unsightly sagging, unless straining bolts are used, which add to the cost of the sytem.. A trellis can be used for support, but a trellis which would cover this area is much more expensive than the system here, which only costs about 10 GBP in materials. The wooden pieces are 2.4 m long. It only takes a short time to construct and it's supported by the lower part of the vertical piece, with one fixing higher up to the wall. Whereas a trellis and a system using wires need two supports, this only needs one.
More spokes can be added if necessary. The extra spokes add very little to the total cost. A rim can also be added very easily, made up of wooden elements or, alternatively, one continuous loop of wire. To prevent the wire from sagging, a small straining bolt can be used - a system which uses horizontal wires needs multiple bolts. Other loops of wire can be installed, inside the outer rim. The system is provided with holes on the main spokes for fixing of additional wooden members or wire loops. All these additions give further securing points for plant stems, although the basic structure is likely to offer enough. An extension is provided for the vertical member, to anchor the structure in the soil.
This is a larger support star, with a shorter vertical, to be used to support a climbing rose ('Compassion'). The vertical element can be extended as the rose grows.