Introduction: water collecting, water conservation

Introduction: water collecting, water conservation




Above, Above, an early use of a water collecting surface, in my lower growing area. The plastic surface supplies a below-ground storage container. Also shown, an early wooden composter. On the left, two circular structures with netting for plant protection. To the right, structures for support of runner bean plants.

The structures and the techniques I use for water collecting  are much more varied and elaborate now. They are described on the page Gardening / construction: introduction, with photographs in the section for 2018. Here, I provide further information, about, for example, the materials and equipment I use, including suppliers. As on the section for 2018, I've more to say about water collecting  than water conservation, but I do include some material here on water conservation techniques, for example, the use of mulches

Often, I draw attention to some additional advantages of materials, equipment and techniques for water collecting and water conservation. They can be used to provide benefits in areas other than water collecting and conservation. Relying on mains water less, or not at all, isn't achievable without expenditure of money, obviously - and isn't achievable without work, and sometimes hard work, and the expenditure of time, equally obviously. The time, money and effort can always be devoted to other objectives - and not just objectives to do with growing. It's easy to justify if the benefits are more wide-ranging.

Like water collecting and conservation, composting can provide real benefits. Not much money has to be spent to carry out composting - a proper composter isn't a necessity at all - but the results can't always be justified, it may be felt, by the care and the effort. This is also the case with water collecting and conservation. The benefits of providing water for plants without dependence on mains water, or not nearly as much, can surpass the rewards of composting, in my experience ,but the work and time required are much greater, and the expense much greater too.

I don't provide guidance at all on 'standard stuff.' I don't explain how to construct a pond for storing water - and helping wildlife and creating, if possible, beauty. Helpful information about excavating, laying pond liner and filling the pond with water is plentiful. I don't explain in very great detail how to construct the water collecting surfaces I've designed. I hope the information I do give will be useful. It generally concerns matters which aren't standard. To give a minor example, it can be much more convenient to fill containers with water to weigh down the edges of pond liner before starting to fill a new pond with liner rather than to use rocks or bricks. Water containers weigh not nearly as much as rocks or bricks, until they are filled with water. It's less effort to bring them to the site of the pond, unless a quantity of rocks or bricks is near the site to begin with. Even then, rocks or bricks may damage the liner, whereas a water container with rounded edges and contours won't.



















 

 

 

 

 

 

Introduction: composting
Hedge, wall and fence composting
Obtaining compostable material and bed-extension
Disadvantages of plastic composters

Structures and techniques: composting, water collecting, water conservation


The main composter
Turning the heap
Other aspects of composting

Using the right tool
Making tall raised beds

See also other gardening pages:

Gardening/construction: introduction, with photos
Gardening: beds and boards
Structures: plant protection and support
Structures: greenhouse and cloches

Some design principles in gardening

Introduction: composting



Above, the main composter.

There are TV programmes which pretend otherwise, but fruit and vegetable gardening on any scale, for any length of time, involves disappointment as well as fulfilment. The harsh realities come in many different forms: weeds, the worst of which can seem like one of nature's bad jokes, although it would be difficult to see the funny side of Japanese, giant or hybrid knotweed or some other weeds, pests - insect, bird, mammal and human (allotment vandals included here in the category of pest),  plant diseases, pests which spread plant diseases such as aphids, weeds which are the hosts of disease-causing organisms (yet another disadvantage of weeds), watering in times of drought, the time-consuming watering which isn't just a token gesture but enough to satisfy the voracious thirst of potatoes and other crops and ensure a good yield (subject to potato blight and perhaps other diseases), the difficulty of obtaining a good yield.

Even if most things go well (it's unlkely that all things to go well - if temperatures are right and rainfall is just right, not too much, not too little, things are going well for the weeds as well) then there can still seem  a disproportion between effort and yield. Some crops are markedly superior to others in this regard. Runner beans give a better yield than broad beans, courgettes give a better yield than peas.

Composting gives a low yield. The  disproportion between effort and yield is very marked. A huge mass of compostable material gives not nearly as much compost as the gardener would like or the soil needs. To collect a huge mass of compostable material in the first place is very often impossible, or requires so much effort. The end product is very desirable, but its contribution to soil fertility is more peripheral than central. In economics, there's a great gulf which is often cited, the gulf between infinite wants and scarce resources. In gardening, there's a gulf between the needs of the soil and the scarce resources of compost.

Every gardener should compost - it would be a breach of gardening ethics in most cases not to compost material which can be composted, or have the material which could be composted transported to a distant site - but a gardener has to be careful not to give too much effort to composting at the expense of other gardening tasks, and non-gardening tasks and duties, for that matter.

There are many  dedicated composters, as well as fanatical composters, who devote great effort to securing diverse materials to build a well-balanced heap and who turn the heap to ensure that the heating effect continues. At the end of it all, the compost they produce is still a marginal product.  Manure, unlike compost,  is generally obtainable in large mass and makes correspondingly greater contributions to soil structure and soil fertility, despite the lower concentration of plant nutrients in manure. Composting should be viewed as a gardener's duty, an absorbing interest as well, perhaps, but no more than that, and certainly not the semi-sacred preoccupation of some organic gardeners.

My discussion here is in accordance with this thinking. I discuss ways of increasing the supply of compostable materials and ways of saving work -  the work of bulk handling, when compostable materials are available in quantity, and work once the composting process is under way.  I also discuss compost containers - plastic, traditional wooden, and the composters I use myself, designed to minimize the effort in producing compost: this valuable material, but one whose worth can easily be exaggerated.

So far as possible, composting should be integrated - unobtrusively, as I see it - into the other aspects of gardening. I discuss some gardening techniques which have a linkage with composting, such as hedge-cutting and weed clearing. Although nettles are a much finer compostable material than hedge clippings, hedge clippings may well be  obtainable in much greater masses than nettles.

As well as the composter above, I use composting systems which have a larger area than most of the ones commonly used, including hedge composting (there's also wall composting and fence composting). These techniques don't make use of a compost bin. 

Hedge, wall and fence composting

These are all forms of composting at a boundary. I use hedge composting in both the upper growing area and the lower growing area, in both cases near to a privet hedge. I use a long strip of land next to the hedge, about 035 m wide, as a long composting area. The hedge forms one of the long sides. The other long side is formed by boards supported by stakes, the system explained on the page beds and boards. This is a very flexible system. The boards can be moved very easily, for example nearer to the hedge or further away. When I work on beds near to the hedge, it's convenient to throw weeds and other suitable materials into this composting area by the side of the hedge rather than to take them to a compost bin or to put them in a wheelbarrow which then has to be wheeled to a compost bin. The materials are out of the way and if they're the least bit unsightly, grass or other things can be thrown on them to cover them up. The compost materials will play a part in hampering the sideways growth of the privet hedge. - these hedges grow outwards as well as upwards, of course. Whenever the hedge is trimmed, clippings fall onto the compost area, increasing the compostable material and avoiding the need to transport the clippings to a separate composter. Other boundaries, walls and fences, have similar benefits, except, of course, the benefits of restricting growth and the benefits of clippings, unless a fence supports climbing plants which are sometimes trimmed. I can't claim that this is an important source of compost, but it makes a contribution and it has a range of other benefits. Upward growth of one of the privet hedges is checked by a novel technique - using the top of the hedge as a growing bed! It retains most of the growing medium during a growing season. Since roofs are often used for growing, why not use the tops of hedges? I'm not a great admirer of privet.

Obtaining compostable material and bed-extension

To begin with, I emphasize the well-known fact that cooked food, bread, cheese, anything that omnivorous rats can eat, should never be regarded as compostable.

Even a large allotment or garden produces a very modest supply of compostable material, and even in autumn, when such plants as  runner bean, courgette and tomato are generally  available for composting.

Anyone who takes on an overgrown, neglected garden or allotment is  fortunate, although it may take time to realize this. An overgrown hedge 5 metres or more high is a great asset. Placing a composter near to a hedge like this is often a good idea, or composting near to it without using a composter.

I've made extensive use of twigs and the smaller branches from nearby hedges to extend the growing area: 'bed-extension.' This is a form of composting. The twigs and branches form an open network, allowing weeds to continue growing for some time (the weeds include grasses, and not just 'weed-grasses' such as couch grass.) The weeds contribute nitrogen, helping to offset the woody twigs and branches, which are high in carbon. I place a thick layer of manure over the twigs, preferably manure in clods or coarse pieces, which will remain on top of the twigs and branches and not fall through. Some of the nitrogen in the manure is washed away to the deeper level and helps to speed up the breakdown of woody material. In less than a year, crops can be grown in the area, although not crops such as carrots, which are harmed by manure. Soil is spread on the manure before planting. Only a thin layer is needed.

Books and articles often stress the need for a mixture of materials, giving a good balance of textures and a suitable ration of nitrogen to carbon. What they don't stress is the disproportionate effort often needed to ensure this, the difficulty of obtaining sufficient of these varied and contrasting materials. A compost heap made up almost entirely of hedge cuttings, high in carbon, with a very open texture, despite the leaves, is well worth having and certainly much better than nothing. There's no need to worry unduly, or at all, about bringing up materials with a less open texture, with a greater concentration of nitrogen, if they are unobtainable. In time, the hedge cuttings will form good compost, even if, as always, there isn't enough of it. Lawrence D Hills claims (in his classic but flawed and outdated book 'Organic Gardening') that hedge cuttings thicker than a pencil won't decay in a compost heap. This isn't true, of course - given enough time, all wood will decay, whatever the size - but it's a good rule for the short term.

A powered hedge cutter or shears can be used for mildly overgrown hedges, but for grossly overgrown hedges, I've used a different tool, a small hand-saw and loppers. I use loppers to detach many of the smaller branches, giving access to the larger branches, which I saw away. Before very  long, a grossly overgrown hedge has been reduced to a short, very bare-looking one, which will, however, revert to its previous size if allowed. A powered brush cutter or chain saw can avoid some but not all of this work.

During the season when the pictures on the page Photographs 2 were taken, I spent a very great deal of time constructing the wooden paths, designing and constructing the raised pond and composters shown on the right, designing and constructing transframe, and on all the other work of the allotments - and, amongst other things, watching the flight of swifts. There was no time to see to the privet hedges, which grew to a great height. When I did cut them to a fraction of their overgrown size, I piled up the cut material:

This is an area which, like the area occupied now by the raised pond and composters, and adjoining it, was obviously used as a dumping ground at some time in the past. Plastic, glass and metal were visible. The soil was only of an adequate depth  in one very restricted area, where I planted an apple tree, just visible, with its supporting stake, in the photograph above, taken  later in autumn.

Since the photograph was taken, I've added a thick layer of manure and a thin layer of soil and the bed is now available for planting. Without an enormous amount of effort, a large bed has been created. I've followed the same procedure to make a second, smaller growing bed.

When possible, composting should be in situ, or not at a great distance from the compostable materials.  Bulky compostable materials should so far as possible be composted near to the supply of bulky compostable materials. Composting can often be carried out at the place where compost will be needed - composting on the growing bed, or the weed-infested ground which will be converted to a growing bed. A compost bin can often be placed on a particularly rampant area of weeds. They will continue growing for quite some time and well benefit the mix of compost materials, without any effort in cutting and transporting them. There are any number of other activities which can be carried out in the time saved.

Disadvantages of plastic composters

Plastic is generally the best material to use for a water butt - making a watertight wooden container isn't an easy matter - but not at all the best material to use for a compost bin, even when the plastic is recycled. There are various objections to the use of plastic compost bins:

  1. Recycling plastic uses large amounts of energy. This energy cost has to be set against the environmental benefits of breaking down kitchen or garden waste into compost in a plastic bin. The resources a plastic container wastes can be considered more significant than the ones it saves.
  2. Unlike metal or glass, which can be recycled many times, plastic in general can only be recycled once, due to contaminants. It's very probable that the plastic will end up in a landfill site sooner or later.
  3. Plastic is discordant in a garden or allotment, a synthetic material at odds with organic life. It's far better to restrict its use to things such as water butts where plastic is obviously the best material to use.
  4. Wooden bins are far more flexible than plastic bins, and can offer better insulation when they are placed next to each other. Three wooden bins can be placed in contact, giving the same benefits for heat insulation as three terraced houses in a row, which insulate each other. Three plastic bins are only available separately (although it would be quite easy to manufacture a set of three adjoining plastic bins) and have the same disadvantages for heat insulation as three detached houses. If a large amount of composting material becomes available, the volume of a plastic container can't be increased to take all the material.

I used a Rotol plastic composter for a time, many years ago. It can produce very good compost and the design has undeniable appeal - a conical shape which looks very good. For all that, the Rotol has the disadvantages of other plastic composters. The top diameter is 45cm and through this fairly small opening all the compostable material has to be inserted (after being lifted up to a height of around 75cm.) The Rotol composter is made of unrecycled plastic.

Composters, then, if at all possible, should be made from a renewable resource, wood, and if it can be obtained, reclaimed wood.

The main composter

This is an improved wooden composter. One advantage is that it can be placed on sloping ground.

The upper surface of the composter can be of varied materials. The version shown in the image towards the top of the page has an upper surface made of wood. This can be replaced with a  PVC top is dual-function. It can be used for rainwater collection, if the composter is on sloping ground - the slope may be a very gentle one -  fand or increasing the temperature inside the composter. The greenhouse effect increases the temperature inside polytunnels and cloches as well as greenhouses, but it can also be used to increase the temperature inside a composter. The biological processes which produce compost are speeded up and the compost is made in less time.  When the composter is empty - and when the composter is almost full - materials for composting can be grown inside the composter to make a contribution  to the common problem, lack of compostable materials, and the PVC panel enables them to be grown more quickly.

The composter is solidly constructed and large but it can be moved from place to place without difficulty, after it has been dismantled. (When I constructed a solid and large workbench for my workshop, I designed it to be easily moved. The bench can be raised using a hydraulic jack, castors can then be fitted and the bench can be moved from place to place. Alternatively, the bench can easily be dismantled and the separate parts taken to a different location and reassembled.)

Turning the heap

The Centre for Alternative Technology's Factsheet  on composting is completely realistic in stating that very few people turn the compost heap, even if they have gone to the trouble of forming a heap which has heated in the first place. The heap is turned - if at all - after the temperature has reached a maximum and has then begun to fall. This is because moving such a heavy load deters almost all but physically strong and very committed people. Cold composting, which may take a year or more to make compost, is the dominant method of making compost now, and not just because, unlike cold composting, it doesn't require a large mass of material to start off the heating process. It requires far less effort than hot composting.

When the improved wooden composter is placed on a slope, then the physical effort required becomes easier. Gravity aids the process of moving the material and whilst the material is being moved, mixing and re-distribution take place. Growers who use a sloping composter will find that the system makes hot composting more practicable. Hot composting has great advantages. It can make compost in about six weeks and is far more efficient in killing  disease organisms and weed seeds. Using a sloping composter,  gardeners may well find that hot composting doesn't require enormous effort.

Other aspects of composting

I don't deal here with large-scale composting, the composting systems needed if compost is to be sold, the composting systems subject to legislation, the composting systems which require an energy input (such as the composting systems produced by Accelerated Compost Ltd) with in-vessel composting systems in general.

The advantages of the restrictions? The advantages of composting in the garden or allotment, rather than sending the material to an in-vessel composting system, are very substantial ones. Compostable materials are mainly water, and transporting heavy masses of water - along with the valuable organic matter - may make economic and environmental sense, or it may not. Not if the distance is great. Like paper recycling, organic waste recycling can have great benefits, negligible benefits or no benefits at all, and one of the most important considerations is the distance the compostable material has to travel - the 'composting miles.' The reason is to do with use of fossil fuel, of course. In situ composting, composting in the garden or allotment, has the advantage of composting distances amounting to yards not miles.

Another advantage of in situ composting is the benefit to wildlife, unless the composter is a closed vessel, such as a compost tumbler. The composter as a valuable wildlife habitat is often overlooked, but Ken Thompson's very lively, very interesting and very informative book 'No Nettles Required: the reassuring truth about wildlife gardening' outlines the advantages to wildlife. Ken Thompson is a researcher at Sheffield University and his book gives some of the findings of the 'BUGS project.' BUGS stands for 'Biodiversity in Urban Gardens in Sheffield.' The project was supported by the major government funder of environmental research, the Natural Environment Research Council.

Of compost heaps, he writes (Page 76, 77): 'Unfortunately, the BUGS project had neither the time nor the money to look at compost heaps in detail, but other research (much of it from Scandinavia) reveals that compost heaps are hugely important wildlife habitats in their own right. This is because warm, decaying plant material is a habitat that would otherwise be absent from gardens. Reptiles in particular like these conditions, and a survey in Bristol found that gardens with compost heaps were twice as likely to have resident slow worms as those without compost heaps. Given the appetite of slow worms for slugs, this has to be another good reason for starting a compost heap...compost heaps go a long way towards replacing a whole catalogue of wildlife habitats that would otherwise be rare or absent from gardens, and are increasingly rare in the wider countryside. Another interesting feature of compost heaps is that by providing a warm, insulated habitat, they allow many species to spread further north than they would otherwise do. Many native species live further north in compost than in any other habitat...' And, in a summary box: 'Compost heaps are...a uniquely valuable wildlife habitat...No gardener with any interest in wildlife should be without one, however lacking you may be in the raw materials.'

Using the right tool

Using the right tool  saves a great deal of work in compost making, as in other gardening activities. In this case, the correct tool is a manure fork. 'The Organic Gardener's Handbook' by Margaret Elphinstone and Julia Langley' is excellent, and has a very informative chapter on tools. This is their section on the manure fork:

'The manure fork is related to the pitch-fork, designed to lift material and throw it or load it somewhere else. It is the most useful tool for building compost heaps. You can use it to load seaweed into sacks on the beach, to throw muck into a trailer, to mix up your weeds and grass mowings into a good compost ... It is a pleasant tool to use properly, because when rhythm and balance are right there is very little strain involved. You can shift a ton of manure with no aches to show for it, and work comfortably all day with it at a steady pace.

'Manure forks have four or five rounded prongs which curve upward, and the prongs are set at an angle to the shaft to assist the lifting movements for which it is intended. If you cannot find a manure fork at your garden suppliers, try an agricultural store.'

Agricultural stores are well worth a visit - well worth regular visits - as a source of garden supplies.

Making tall raised beds

A photograph of some of the tall raised beds is provided to illustrate the section below on Rainwater collection, but for convenience I provide the photograph here as well:

The very tall raised beds on either side of the pond (there's another raised bed out of sight, to the left of the trellis) needed a sizeable quantity of a 'growing medium.' Obtaining sufficient soil to fill the beds would have needed a great deal of work. This is the  method I've used in this area and other areas. I've added only a small quantity of soil. I depend upon the fact that quantities of compostable material will be available later. I began by adding a thick layer of  hedge clippings, with thick stems, which are available in quantity. I aimed to preserve the open texture of this base layer. The vegetation growing here, such as nettles, could carry on growing relatively easily, for quite a time. Eventually, it would die, but the green material would fill the spaces in this layer. On top of the base layer, I added manure, in large pieces. (Large clumps dug up with a spade could have been used as well. These large pieces formed a foundation for the finer material to be added, to prevent the finer material falling into the base layer and filling the spaces. On the manure foundation, I added what compostable material I had at the time and a layer of soil. To summarize, the layers are these, from ground level up:

Hedge cuttings, with thick stems.
Large manure pieces.
Soil and compostable material.

Eventually, the soil level will sink and can be topped up with new compostable material (and manure and soil, if available). The technique allows growing to begin, without the work and delays of importing sufficient soil to fill the containers.

Hedge, wall and fence composting

These are all forms of composting at a boundary. I use hedge composting in both the upper growing area and the lower growing area, in both cases near to a privet hedge. I use a long strip of land next to the hedge, about 035 m wide, as a long composting area. The hedge forms one of the long sides. The other long side is formed by boards supported by stakes, the system explained on the page beds and boards. This is a very flexible system. The boards can be moved very easily, for example nearer to the hedge or further away. When I work on beds near to the hedge, it's convenient to throw weeds and other suitable materials into this composting area by the side of the hedge rather than to take them to a compost bin or to put them in a wheelbarrow which then has to be wheeled to a compost bin. The materials are out of the way and if they're the least bit unsightly, grass or other things can be thrown on them to cover them up. The compost materials will play a part in hampering the sideways growth of the privet hedge. - these hedges grow outwards as well as upwards, of course. Whenever the hedge is trimmed, clippings fall onto the compost area, increasing the compostable material and avoiding the need to transport the clippings to a separate composter. Other boundaries, walls and fences, have similar benefits, except, of course, the benefits of restricting growth and the benefits of clippings, unless a fence supports climbing plants which are sometimes trimmed. I can't claim that this is an important source of compost, but it makes a contribution and it has a range of other benefits.

Rainwater collecting: introduction

Gardeners in arid areas have always had to find ways of saving water. Now, in this country, rainfall isn't taken for granted, and there's more and more interest in ways of conserving water. In this section, I discuss amongst other things ways of collecting rainwater from hard surfaces such as paths.Gardeners in arid areas have always had to find ways of saving water. Now, in this country, rainfall isn't taken for granted, and there's more and more interest in ways of conserving water. In this section, I discuss amongst other things ways of collecting rainwater from hard surfaces such as paths.

Techniques and equipment  which don't work or which require an  effort completely disproportionate to the results should  be abandoned or modified or at least recognized for what they are: token gestures. An example: water butts, intended to make a contribution to water collecting. Their contribution is negligible. This is for the obvious reason that the collecting area is very small. For a water butt with a diameter at the top of 0.4 m (there are many water butts with smaller diameters than this), the collecting area is only about 0.12 square metres. In general, even five water butts will collect a negligible proportion of the rainwater which falls on a growing area and will make a negligible contribution to satisfying the demand for water. Virtuous feelings of contributing to 'conservation of resources' aren't sufficient justification.

Water butts are most useful for storing water which has been supplied by a tap - if, of course, a mains water supply is available. There's a water tap near to my allotments, but the supply of water has sometimes been interrupted and this has happened in spring, during a period of extended drought, when I was planting asparagus and other crops, I used up all the water in the large tank which stores water collected from the greenhouse roof, which holds 1 000 litres (a tonne of water) and after that, my only supply of water came from the small pond in the upper allotment. Since then, I've extended the facilities for water collection and storage in the ways I describe here. If gardeners in this country can't take for granted an assured supply of mains water and adequate rainfall, gardeners in arid climates face much greater difficulties, of course. It's possible to collect only a proportion of the rainwater which falls on a growing area or an area near to the growing area. It's obviously not possible to make the whole of a growing area into a collecting area, but it's necessary to have available collecting areas much larger than the collecting area of a water butt, or a number of water butts. I use paths and reservoirs to collect water.

Rainwater collecting: using paths

 

In this photograph, just visible, on the left, is a black water butt in my lower allotment. The water butt collects a little water but its main use is  to store water from a much larger collecting area. (The wooden structureto the right of the water butt is a transframe, shown here with only a PVC top-panel, no side-panels. The PVC top panel can be fitted with a section of guttering and can be used for water collection too.)  The  two principal hard surfaces shown in the photograph are  the two paths constructed from wooden boards, with raised wooden edging. I've laid down heavy-duty plastic sheet material on the path on the left and covered it with netting (not clearly visible in the photograph) so that it's possible to walk on the path without slipping. The rainwater which falls on the path runs down  into a container at the bottom of the path, buried in the soil. A wooden board covers the container. Containers of very large capacity are obtainable which can be buried in the soil, but the container here is much smaller. At intervals, I pump the water from the buried container into the water butt, using a  hand pump.   The pump can be used to pump water to growing areas or other water storage containers uphill. Alternatively, a watering can can be  submerged in the water container. This is often a convenient way of using the water.

This method of collecting water wouldn't be possible in the case of a path which is on level ground, but the slope needn't be at all steep. Paths on gently sloping ground can be used for water collection.

The system shown can be regarded as a prototype, but the only  improvements needed are to do with appearance, not functionality. The system works perfectly, and the volume of water collected is substantial - given a modicum of  rainfall, of course.

More recently, I've developed techniques, not described here, for rainwater collection which don't require the conversion of paths.

Rainwater collecting: a raised reservoir / pond

The image shows  another large water collecting surface, a reservoir. 

The bulky material on either side of the reservoir withstands the pressure exerted by the water in the reservoir. There are supporting structures hidden from view but these are cheap and simple to make. Their role is to support and keep level the rectangular edging of the reservoir. The reservoir can be constructed on sloping as well as level ground - the ground here is sloping and uneven - and doesn't require a wall as the boundary on one side. It can be constructed anywhere in a growing area, in fact.

The wall here is south facing, so this is a very favourable situation for growing, but the soil in this area is very thin. Beneath it is a deep accumulation of rubbish which must have been deposited a long time ago - broken glass, rusting metal and plastic.  The  beds on either side of the pond allow crops to be grown here now.   

The reservoir is functional. A primary function is collection of rainwater which can be used to irrigate crops, using the handpump, water syphoned from the reservoir or a watering can. It would also be possible to add an overflow system which includes piping. It's intended, though, to be more than functional, a pond  So, one of the things I've planted in the pond is the native white water lily, Nymphaea alba  (dormant at this time of year, of course). The rectangles of soil and water form an effective contrast, I think.

This shows the areas of the water-collecting surfaces in my allotments in square metres.

water butt 0.4
small pond 0.7
PVC top-panel of transframe 1.5
reservoir 2.7
water-collecting path 6.3
greenhouse 36.5

The greenhouse is a comparatively large one, over 11 metres long. Growing areas are water collecting areas as well, of course, but not the growing area inside the greenhouse. The large contribution to water collecting made by the greenhouse roof is subject to this {restriction}, then: not all the water collected by the greenhouse roof can be used in other areas.

 The water collecting path is narrow. Adding a water collecting surface to the wider and longer curved path to the right would increase the water collecting surface significantly. The method used for a straight path has to be  modified for a curved path but is straightforward to implement.