Proven to Work Tips on How to Edge Garden Abyss...

Turn not the first sod, until you have mentally pictured the whole project right through to ‘pointing’ your last slab.

There seems to be many people that think creating a pool, even a water garden, is just about digging holes. As a landscaper I often found myself being asked to view the site of a potential water garden with the assurance: “We’ve done most of the work, we’ve dug the hole”.

Then I’d arrive at the site to be presented with a site not unlike a film set facsimile of a scene from a 1st World War battle of the Somme and an enormous bomb crater. This would only serve to confirm that the process just had not been worked out at all. I would return home, sketch out a plan and spend the best part of 4 hours, working out a detailed price, whilst seeing the costs of the excavation pale into insignificance against the equally onerous expenses of lining, power supply for pumps and for would-be koi keepers, and filter systems themselves…….

And then there was the edging.

How was the pool to be finished off? Then, what was going to support the liner around the top edge? If it was just going to be soil it would have to be a “natural looking” pool in a wild area of the garden.

But even these water gardens must have the liner must finish somewhere, tucked away and hidden and that requires some forethought and some design in the excavation. In both the informal landscaped garden and the formal, neat or stylised pool perhaps in a patio area, there has to be a support for the liner and a visually definable point at which water ends and another surface takes over. At that point the liner needs support and the material that borders the pool needs support.

This is even more important in sloping ground where the top edge of the pool emerges above ground level. Here you need skeletal support. Water is floppy but heavy stuff and it needs firm containment and it all adds to the expense. Then you need to hide how this is done, and that material needs to be in tune with the whole design of the garden.

(Drawing 1: The simplest method of pond construction and dealing with the problem of what to do with the edge.)

Anyway back with my aspiring pond owner, I very often knew that just the cost of the liner would be enough to dampen the spirits and that all my work on estimating and any other expenses would be wasted, but in considering the options we all learnt a little and I became ever more determined to give up landscaping.

SO WHAT WERE THE OPTIONS?

Starting off with the simplest option, using a flexible liner and just hiding the liner around the top edge. The top of the liner is tucked into and up the outside edge a 45° groove around the shape of the pool.

The British Trust of Conservation Volounteers adopts the simple method for their pond construction. They use just Holme sand to line the pool and to fill the ‘v’ trench or groove round the edge. This is layed on top of a protective underlay over the liner.

This will be filled with soil or sand and topped of with inert gravel. The inside level of the groove must be cut level a little below the height of the liner on the outside of the groove to ensure water laps over into the groove that will be either a beach area and or the marginal planting area when the plants soon mask any definable edges

Plants will soon mask the edges. This is the most popular method for conservationists, wildlife gardeners and Euro pool builders. However, it does not allow for a lot of human traffic around the edge especially in the wetter months.

The usual method of overcoming this is by suspending some decking over the edge.

This allows man to observe the contents of his pool at close hand without encroaching too much on the idyll of his creation.

 

Suspended decking hides the edge effectively

The beach area, as it will seem, can be made to look more ambitious and less contrived with a mix of larger pieces of rock and stone, but these have a tendency to sink over a period of time and get in the way when it is time to clear out the plants.

 

A mix of large and small stone gives the beach more credibility.

Plant maintenance is another bugbear since most of our rugged native marsh lovers, given a whiff of the empty bog rimming this pool, will be off like a shot and instantly entwining on a root level with long lost soulmates on their circumnavigation of the pool. Four years down the line, the net result is a giant circular sausage of root.

 

 

The giant sausage roots can only be sawn apart to remove them

Apart from that, the more ambitious and adaptable marginals seemed to have leapt out and interknitted with the surrounding grass, soil or even gravel, firmly anchoring the sausage in place.

ESSENTIAL REQUIREMENT FOR ANY ALTERNATIVE

Where the surface of the water ends and a new surface begins, is where the liner is supported up to the ordained water level. This is where an edging material like slabs or timber disguises the liner. It can be supported on the structure that supports the liner, which in turn can be a visible and useful part of that structure, like facing the inside, or outside of the pool if it is raised, in the form of a stone wall, timber face or rock edge. Whatever way you decide to do this, you must first establish the marginal planting level. This is where the plants can sit in aquatic planting baskets up their necks in water. This will be a level that is no less than 220mm below the final water surface.

Excavation ready for a liner. Here many landscapers would have cast a concrete ring at the shelf level before completing the excavation. The landscaper here thought the integrity of the compacted soil was firm enough to take stone straight onto it.

There are some landscapers that will excavate the whole shape of the pool down to this level and will cut a trench down 300mm and around the whole circumference of the excavation. This will be the width of the desired marginal shelf and then plus the width of the facing material, be it building stone or rocks. Pegs will be driven into the trench to establish a precise level to which a concrete mix will be poured. This can be delivered “Readimix” for big projects or a home-made concrete mix of 4 parts 15mm chippings, 2 parts sand to 1 part cement. Once the concrete is set you dig down within it to the final depth that you envisaged the pond would be.

What you are left with is a concrete ‘donut’ that will provide effective support for any heavy rocks or walling that you may use to face the inside of the pool. This is a technique favoured by the ‘big-boys’ like Dougie Knight and the Tinsleys that are often looking at rocks as edging stones of between 2 and 20tons, where they will use 100mm to 200mm renders of reinforced concrete rather than flexible liners.

Pool edging Tinsley style

If your project is relatively modest and the soil is firm and undisturbed, you may feel that the concrete ‘donut’ is not necessary and that it would be adequate to just cut the level and the profile of the marginal shelf into the soil, lay the liner on an underfelt or sand bed and then lay any rock work on top of that with underfelt or a mortar mix to cushion the liner. Many landscapers that don’t make water gardens a speciality will do it this way and haven’t yet learnt there is an element of Sod’s Law in this. They build up the facing stones on the inside of the liner and pull up the liner behind to the level required. The liner is then wishfully held in place by soil, hardcore for a path and paving slabs.

Stones go in on the shelf.

 

 

 

 

 

 

…the liner is pulled up behind the stone work.

 

 

 

 

 

 

…similarly.

 

 

 

 

 

 

In a level lawn the end result looks great.

Personally, I have always been happier building a concrete block skeleton laid on the marginal shelf level, to establish a permanent visible level at the water level. It is easy and firm to work to and provides a positive support for the edging right at the water’s edge. They are also a neat face to work to in the event of having to dress a raised pool or pool emerging out of sloping ground.

 

Treble landscapes show how to do it. Two different stages of two very similar projects

 

 

 

Rather than use concrete blocks, there are advocates of the ‘donut’ at water level, when concrete is poured directly into a trench 250mm deep cut on the perimeter of the pool shape. The soil then can work as shuttering. Once the soil is dug away on the inside of the ‘donut’ it will provide direct support for the edge of the liner and provide firm support to any edging stones or slabs sitting just above the water.

If you want to dispense with any facing to the inside of the pool to keep the effects of the concrete on the fish to a minimum, an overlap of the edging slabs by 25 to 30mm is enough to shade the liner out of sight and mind. The depth of the blocks is the same as a large marginal planting basket – the perfect depth for a marginal shelf.

The marginal shelf is left at the depth of the concrete block.