Creating Garden Ponds

It goes without saying that water is a vital part of any garden but it can provide so much more than just being fundamental to the growth of plants. Water used in ways which create still, reflective surfaces has the ability to produce a feeling of rest, peace and relaxation.  With the aid of a pump the same water body can also provide a more dynamic feel with the wonderful movement and sound of water from waterfalls or fountains which can literally be switched on and off as required. The garden pond can also be home to a whole range of plants, insects and other animals which otherwise might not be able to visit or survive in the garden. Someone once said “build it and they will come” and this is definitely true of a garden pond which introduces a whole new environment and dimension to any garden. Water indeed seems to hold a fascination for most people all of its own. How many times have you visited a garden and despite all its other attractions either headed straight for a water feature or been lifted in spirit by suddenly coming across one? The design, the way it fits into its surroundings, the unusual plants and all the life that the water contains holds a fascination for both young and old. It has been for all these reasons that wherever I have gardened over the years I have always added some form of water feature and I have always felt that both I and the garden have been better for it! I hope therefore that what follows will encourage you to at least think about doing the same.

At this point I think it is necessary to issue a short health warning. Clearly water can be dangerous and this should never be overlooked. Even the shallowest pond is deep enough to drown someone, especially a small child, and therefore should not be constructed where unsupervised children are liable to play. Water and electricity are also a dangerous combination and need to be treated with respect. If at all unsure leaving it to a qualified person is my advice. However, if you do decide for these or any other reasons that a pond is not for you there are still lots of ways of enjoying the movement and sound of water in the garden by using self-contained and re-circulating features such as pebble fountains and all sorts of sculptures and naturalistic designs. Have a look at the Old Railway Line website for some ideas on what is available. Those of you who were able to visit the garden centre in the summer and autumn will already know that they have greatly expanded their water gardening section offering plants and fish in most seasons as well as all the accessories needed for successful water gardening.

If at this point you have decided to explore the idea of creating your own garden pond this is an excellent time of year to make a start. The physically hard part of the process, the digging of the hole, can be done at a time when there is less to do in other areas of the garden. Hopefully as a result the new pond will be filled by spring by which time pond plants will be becoming available at garden centres or when friends and neighbours might have excess plant growth in their own ponds which they are happy to share with you. This is a great way of getting a new pond to come ‘to life’ as shared plants often bring with them lots of often unnoticed but very welcome pond life. Just be careful not to accept offers of invasive plants of which I will write later. If you intend to add fish to the pond this can be done a month or so later at a time when aquatic centres will have their new stock available. By the end of the summer you won’t believe how good your pond is looking!

Before putting the spade to the ground, however, there are a few decisions to be made. These include choosing a suitable site, choosing a design which fits in with the rest of the garden and deciding on the method of lining the pond in order to make it watertight.

The good news about choosing a site is that ponds do not require perfect conditions or pampering  so there is always a degree of latitude which allows gardeners a certain amount of choice of position. The single most important consideration is that the pond is planned in terms of the garden as a whole so the layout of the existing garden will help to determine the position and to some extent the size and shape of the pond. Firstly choose a site which has adequate sunlight ie. away from large trees and other features which create large shadows so that the water plants can photosynthesise efficiently and thereby produce the dissolved oxygen which water organisms require. It is true that green algae which can become a problem in many ponds also like a lot of sunlight but it only really becomes a serious problem if there is an excess of nutrients and an absence of predators to control it. Ponds can be sited near to small trees but just remember that leaves can build up in ponds as they decay so it is best to remove as many leaves as possible in the autumn to help maintain water quality. A second consideration might be the actual lie of the land in that ponds which are intended to look ‘natural’ will generally be found in the lower parts of the garden to which water would naturally drain. Once the site is chosen the next decision concerns the shape and size of the pond and as suggested earlier these choices should be informed by the design of the rest of the garden. The shape is often suggested by the degree of formality of the garden design as generally formal gardens are best complemented by formal circular, oval, square or rectangular ponds. Informal designs on the other hand with their sweeping curves and more naturalistic planting are enhanced by ponds with similar curves often in the form of a ‘kidney’ shape. Size will also be suggested by the surrounding design and size of the garden as a whole so that a sense of balance is maintained. From the point of view of the life of the pond, however, it is always a good idea to make the pond as large as the general design will allow. The larger the pond the fewer problems it will face in terms of over-heating and algae growth and the wider range of wildlife it will attract and sustain. Depth is also a key factor and the general advice is to have some parts of the pond at least two feet (60 cms) deep. This will allow waterlilies to grow well and prevent the pond from freezing solid in a severe winter.

The next decision concerns the method to be used to line the pond and there are basically three ways of doing this- with concrete, with a flexible liner or with a pre-formed, semi-rigid liner. For many years the concrete option was the only one available to gardeners. Today though it is the most expensive as even small ponds require strong walls at least 4” (10cms) thick and involves considerably more physical work in terms of moving and mixing sand and cement than with the other methods. For these reasons and also the fact that all the ponds I have created over the years in my own gardens or for other people have involved the use of the more modern methods, I will concentrate on these two methods. If you are interested to find out more about concrete ponds there is plenty of good advice to be had on the internet and in water garden books.

Flexible pond liners represent the more versatile of the two types as they are not rigid and can be used to create all sorts of shapes and depths of water which tends to produce a more natural looking pond with gently sloping sides. The lining sheets are mainly one of two materials- Butyl rubber or Plastic (PVC). Butyl rubber is generally thicker than plastic and has the ability to stretch a little when  the pond is filled. It therefore tends to last longer, have a longer guarantee, is less shiny but is more expensive than plastic.  Whichever you decide to use it is vital to have enough to do the job in one piece for obvious reasons and the method of calculation is to use the length and the width and to increase each of these by twice the maximum depth with a further 3 ft (0.9m) added to each as an overlap all round the pond. For a rectangular pond measuring 9 ft by 6 ft by 2 ft  the liner length is 9+2+2+3=16ft (Metric 3+0.6+0.6+0.9=5.1m).

The width required is 6+2+2+3=13ft  (2+0.6+0.6+0.9=4.1m)

For an irregular shaped pond it is important to measure the largest length and largest width and then make the calculations as if it were a rectangular pond. This will result in some waste when the liner is finally trimmed to shape after filling but there is no way round this except to create a shape which is not too far removed from a rectangle, square or circle.

Pre-formed, semi-rigid liners are generally made out of fibreglass or some form of plastic with the fibreglass being used for the larger, more expensive shapes. They obviously come in standard forms and sizes and although they have planting shelves at various depths they do have quite steep sides which makes them less natural looking. However, in gardens where space is restricted, for those with stony soils and certainly for first-time pond builders they are well worth considering. In our current garden we wanted to add a wildlife pond but hadn’t the room for one with the gently sloping sides which we would have preferred so we chose to use a kidney-shaped pre-formed liner  measuring about  8 ft by 5ft by 2.5ft deep  (2.4 m by 1.5 m by 1.25m) and we have been delighted with the results. This size was just about manageable for the two of us to lift in and out of the whole during the construction period but I have to say that for any larger pond the flexible liner would be my choice in future.

Although it is of course possible to have raised ponds they require a very strong wall and are therefore technically more involved and expensive than digging a hole and simply sinking a pond into the ground so I refer you again to books and the internet if this is your choice.

If a flexible liner is to be used the outline of the pond needs to be marked out on the ground using a rope, hosepipe or line of sand. Remember that you have probably already bought the liner based on your original measurements so don’t be tempted to make the pond larger at this stage! I imagine that most ponds are created on a grassed area so the turf needs to be lifted first. This can be used to repair other areas of lawn, to extend the lawn elsewhere or can be piled up in an out of the way corner to rot down into valuable loam for later use. The pond can then be dug out in your own time! One good use for the excavated soil is to establish a raised area at one end of the pond which can be used to create a rockery, waterfall and possibly even a stream course. If this is the case put the excavated top soil on one side and use the sub-soil, which will be lighter in colour and probably stonier, to build up the base of the raised area with the top soil added to the top as the final layer. In any digging process it is always best to keep these two parts of the soil separate as it has taken nature a long time to produce the rich top soil and it shouldn’t be wasted! One of the great advantages of using a flexible liner is that you can create not only interesting shapes but that you can also add a variety of depths however, don’t be tempted to make the shapes too intricate or curves too tight  as this leads to a lot of folds in the final laying of the liner. One or two shallow areas around the edge are always worth incorporating so that birds can drink and bathe and hedgehogs and other animals can access and leave the pond safely. It is also a good idea to include several reasonably flat shelves at various depths for planting the water plants which will require different depths of water and at least one deep area over 2ft (60 cms) deep as mentioned earlier. It is also a good idea in my view to aim to add a 2” (5 cm) layer of sand to the whole area before the liner is put into place to protect the liner from any sharp stones which may get overlooked so the pond needs to be dug a little deeper to allow for this. Once the digging is complete any sharp stones should be removed from the sides and base and the ground firmed with the ‘boot’ to consolidate the soil and provide a firm base. Before adding the sand, which always holds better on the sides if it is moist, the area around the edge of the hole needs to be dug out to a depth of about 2-3” (5-8 cms)  and width of around 1ft -1.5 ft (30-45 cms) to make room for the liner overlap and to ‘sit’ the pond nicely into the ground. Eventually this overlap can be covered by the lifted turves of grass or by flat rocks or pebbles. Now is the time to check that the edge of the pond all the way round is at the same level otherwise when filled there will be different amounts of liner exposed and this is the one thing that can really spoil the look of the finished article so it is worth spending time to get it right. Levels are checked by using straight lengths of wood and spirit levels and the edge can be adjusted by adding or removing soil from low and high areas around the edge. Now is the time to add the sand both to the main hole and to the overlap edges. This is just ordinary builders sand and therefore very low cost compared to the liner so is well worth the extra time and effort. I always check the levels again at this stage as it is easy to add or remove sand around the edge at this point. At this stage the liner can be laid but I like to add another layer of protection especially if the soil is quite stony as the last thing you want is a leaky pond! This is a layer of special pond underlay matting which doesn’t need to be laid as one piece, is relatively inexpensive and is much easier to lay than the actual liner itself. Some people use old carpet, carpet underlay or even cardboard sheets instead and these are fine although I think that these are best laid before ie. under the sand layer. Laying the liner itself is not a one person job particularly if you are using the heavier butyl liner so you will need help at this point in the process, the more hands the better really. Position the liner over the hole with an equal amount of overlap on the opposite sides and then let the liner begin to sag into the hole and rest on the base and sides. Place a few rocks or pieces of wood around the edge of the liner to keep in in place as it begins to fill but be careful not to damage the liner. When you are happy with the position of the liner you can begin to fill it slowly, don’t be tempted to rush it at this early stage. Ideally you would want to use rainwater as tap water contains not only chlorine but also dissolved salts such as calcium and magnesium but for most people this is not possible so tap water is the only option. The chlorine will dissipate over the next few weeks and the salts are not likely to be a problem as they are diluted by rainwater over the following weeks and months. However, if possible it is better to top the pond up in dry periods with rainwater so as not to upset the balance of the pond. Water can be stored in butts or even run directly into the pond from nearby gutters. As the pond begins to fill the weight of the water will force the lower parts of the liner to take the shape of the ground beneath and the liner will begin to sink further into the hole and as it does so the rocks or timber around the edge need to be lifted to allow the liner to move. Around the inside of curves the liner will start to fold to take up the excess sheet and these folds can be made neater by hand before the weight of the water holds them down flat. At this early stage just make sure that you have enough overlap all the way round as if you haven’t you will need to get the water out and adjust the liner before starting again! Hopefully you won’t and you can continue to fill up to the top. This is when you will find out if the water agrees with your levelling of the edge! If it is not quite right you can make minor adjustments by adding or removing sand from the pond edge until it is as good as you can get it. You always tend to find that there are one or two areas where the water begins to spill out of the pond first and these will be the drainage points after heavy rainfall and are perfectly acceptable. In fact they are quite useful in that just outside them you can position plants which like a wet soil. At the drainage point of our pond we have planted Cotton Grass (Eriophorum angustifolium) and Lady’s Smock (Cardamine pratensis) both of which love a moist soil. At this point you have a hole full of water but not yet a pond although you are well on the way! Over the next few weeks as you allow the water to ‘air’ you can get on with the crucial work of edging the pond to disguise the liner. This is a matter of covering the overlap once you have trimmed off any excess liner with your chosen material such as grass turves for a really natural look or a combination of flat rocks and pebbles. Pebbles work particularly well where you have gently sloping sides where the pebbles can continue into the shallow water. In my experience covering the liner is a really vital exercise and is worth spending some time on even if it takes a few attempts to get it right. Just work on the principle that the less liner you can see out of the water the better the pond will look.

Digging and preparing a hole for a pre-formed liner is much the same process as above but with a few differences. The main one being that the three dimensions  of the hole are determined by the size and shape of the liner mould and you have to dig a hole into which it will fit with a space of 1-2” all around and a little deeper on the base into which sand will be placed. To start place the mould on the ground where the pond is to be sited and using some vertical canes against the outer edge of the mould lip mark out the shape out on the ground surface. This will give you the basic shape of the pond to start you off with the removal of grass turves and top soil. Keep the mould near to and lined up with the hole so you can attempt to match your ground shape with that of the mould ie. the various planting shelves and ultimately the shape and depth of the base. You will probably need to place the mould into the hole several times before getting a good fit. This is why the mould needs to be of a manageable size for one or two people to handle. Dig the hole a couple of inches deeper and check that there are 1-2” of space all the way round to allow for the sand which will support the sides and keep stones away from the mould, but do remove any that are obvious. Pre-formed moulds are usually quite a lot thicker than flexible liners and therefore don’t require additional protection from matting or carpets. Once you have the hole prepared in this way as with the first method remove from around the edge of the hole the turf or top soil to a depth of a couple of inches and wide enough to accept any rocks which you plan to edge the pond with. This ensures that the pond is sunk into the ground which makes it look more natural and later allows the turves or rocks to cover the lip. At this stage check again that the hole edge is level all the way round and then add a good layer of sand to the base and firm it down. Lower the mould onto it and check that the lip is lined up with the hole edge and that the top edge of the mould itself is level all the way round. You may have to adjust the base several times before you get this right followed by a final check with the lengths of straight wood and spirit levels of the pond edge. I then like to add water just to the bottom part of the mould up to the edge of the lowest planting shelf. This keeps the mould firmly in place and gives you a first sign that you have the levelling right. If you are happy still with the levels you can then add the rest of the sand to the gap between the mould and the hole sides. This will support the sides before you add more water. Just let the sand fall into the space and compress it gently down with a length of wood until the gap is filled to the top. The rest of the pond can now be filled and when it is full you will know how well your levelling really went! Having got this wrong in the past I can’t stress enough how important it is to get the levelling right the first time, especially with a pre-formed liner which can’t be adjusted at the edge as much as a flexible liner. Once this is all done you can concentrate on finishing the pond edge and allowing the water to settle. I prefer to use flat rocks for a pre-formed liner which can be placed so that they fit together quite tightly and overlap and help to hide the liner rim and the top part of the liner sides. They can be left loose but I have found that they can get dislodged by animals and large birds so I cement them in place for a firmer construction. Try to avoid getting mortar into the pond by using it just up to the outer edge of the lip of the liner and not actually onto it. As you can see from the photographs we decided to site our pond at the base of the steps down from the gravel bed so that a small waterfall could be added above the pond. For this we used the same local rough slate that we used for the pond edging. The actual turf and soil from the hole which we could have used for a raised area went instead into a new raised vegetable bed which we were building at the same time.

I am going to end the blog at this point and leave the planting and finishing of ponds to a second blog which will come out in mid-February. Pond plants are not really available until well into the spring and I think you have more than enough information to be going on with! However, as an encouragement to seriously think about creating your own pond I have included a couple of photographs of our pond taken just a few months after it was first filled. It always amazes me how quickly ponds mature and give the impression of being a long-standing feature of the garden.

Don’t forget that you can ask questions or make comments on any of my blogs in the section at the end of each blog and I look forward to hearing from you. Until then keep safe, healthy and get digging!

Keith