Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.
Whilst the digging and shaping of a pond can be arduous and time consuming work, preformed ponds are designed to make the job simpler.
With their hard, molded plastic design, the preformed ponds act as a predesigned shape, meaning that the only necessary step is to dig a hole big enough to set it in.
This takes away the need for manual shaping of the interior of the hole, something that can prove tricky from a design, and maintenance standpoint.
Whereas self-dug ponds (see also our article on pond retaining walls) require stepping of the pond bed, the laying of black, waterproof tarpaulin, and the associated upkeep (such as tending to rips and perishes in the material), a preformed pond is tougher, longer lasting, and often looks smoother (and more uniform) once installed.
Preformed molds also come in a wide variety of shapes and sizes, meaning that you can often have a much more interesting layout design than you’d perhaps be able to achieve via a manual installation.
For the majority of pond owners, it is their source of pride and joy, so achieving an attractive, interesting, and effective aesthetic is of great importance.
But Which Is Better?
One major positive, aside from the aesthetics, is the fact that preformed ponds are generally less expensive than pond liners.
Of course, this depends on the size and depth of the preformed mold, but by and large this is the case.
When combined with the ease of installation, this makes the preformed molds a popular choice, especially amongst first time buyers.
Another positive aspect of preformed ponds is that they are incredibly durable, and can withstand heavy impacts, like for example if stones or tree branches fell into the pond.
This is where they stand apart from pond liners, as these are just sheets of plastic, making them more susceptible to damage from such foreign objects entering the pond.
They also play host to beneficial algae and bacteria that will improve overall health of the pond, as well as the internal ecosystem.
Of course, the negative aspects of the preformed method are that there is less option for customization.
This is because they are an off the shelf product, so they cater to general use.
If you want a design that is more complex, unique, or specifically designed for a garden with unusual or limiting dimensions, then manually digging and using pond liners might be the option for you.
There is also the fact that with preformed ponds, you don’t have the option to extend the existing pond, or customize it should the need arise.
This limits the amount of fish you can purchase and have in the pond, and seriously limits their growth potential.
On the topic of size, most preformed models are generally smaller than self-dug designs, meaning customers are limited to a smaller pond overall.
Of course, this doesn’t mean they are “small” in the true sense of the word.
They are still large and cumbersome in their preformed state, which means a lot of people do not have the means to transport or store them until the installation can begin.
Whilst most companies will offer delivery on such items, it does mean extra expense, as well as the inconvenience of having to wait for delivery before you can install the item.
There are also environmental risks to be mindful of, most notably heaving and sinking.
If the pond is not filled enough (and thus heavy enough), then there is the risk of it rising out of the bed.
Similarly, if there is heavy rain, there is the potential for the weighty pond to sink further into the ground, trapping water between the bed and the plastic.
This is especially true of ground types like clay, which doesn’t allow water drainage to the same extent as normal soil.
The first benefit of pond liners is that they aren’t expensive, making them more accessible to a wider range of customers.
As mentioned previously, with the inexpensiveness indeed comes harder work, but also an added flexibility.
This gives you the option to be more creative and personalized with the overall design of your pond, allowing a one of a kind layout.
You can also expand or amend as the years go on, as the flexible shape of the liner means that changes can be made.
This allows for creativity down the line, whereas the rigid form of the preformed models means digging them out and exchanging them for bigger models should the need arise.
There is also the possibility of establishing beneficial bacteria in the pond floor, as the rough, textured surface of some liners can help microorganisms to grow and thrive, proving healthy and beneficial for the ecosystem of the pond.
Aside from this, they are also watertight, thanks to the synthetic rubber, which is flexible, durable, and long lasting (under the best circumstances).
Of course, the main negative (and the one that dissuades people from choosing them) is the work that is involved.
The shape of the hole needs to be dug to a much higher level of precision than with preformed ponds, and that is before the liner can even be placed.
It is also important to ensure there are no sharp or jagged objects in the bed before laying the liner, as these could penetrate the surface, causing drainage and flooding.
This is also true of any tree roots that could be growing near to where the pond will be placed.
Depending on the size of the tree, and its propensity for growth, this too could puncture the liner and cause the same problems.
If this is the case, then it is advised to line the ground with old carpeting or thick material to act as an extra line of defense between the liner and potential invasive plant roots.
The Installation Process
Installing the preformed pond, whilst a relatively simple task, still needs to be done correctly.
The first thing to do is to choose a spot with a lot of sunlight. At least 4 hours of sunlight will suffice.
This is important for maintaining water levels, as well as for drainage.
It will also ensure that the water within the pond doesn’t get too murky and remains clear and bright.
It is also important to make sure that the area is relatively root free.
These will not cause any damage to the preformed mold, but depending on the size of the roots they could dislodge or offset the balance of the pond over time.
Next, mark out the dimensions of the pond using chalk or aerosol paint, before digging the corresponding hole a little larger and deeper to allow ease of entry, and room to compact and fill in afterward.
Once you have dug the hole to required dimensions, make sure the ground is firm and compacted to ensure a sturdy foundation.
It is also important at this stage to ensure that no obtrusive stones, branches, or roots are present in the space, so as to start with a clear and free base.
Once the foundation has been laid, use play sand (less coarse) to act as a layer beneath the preformed mold.
This will help with firmness, drainage, and cushioning, creating a smoother surface than the ground.
Place the mold inside the hole, layering it where necessary to ensure levelness and proper depth.
For reference, the edge of the preformed pond should be slightly above ground level, so that dirt, soil, rainwater, and any gardening fertilizers or weed killers do not get washed into the pond water once setup is complete.
This will create a slight slope that will prevent any of these adverse consequences.
Once the mold is level and sits securely in the hole, backfill around it with loose dirt and sand, getting about half way.
Then begin to fill the pond with water.
Continue filling the pond, carefully backfilling around it with dirt and sand, monitoring the swell of the mold, as well as the firmness of the ground around it, to ensure it remains secure and tight.
For the best result, try to finish both of those tasks around the same time.
This will allow the loose soil and sand to accommodate the swell of the mold, creating a firmer seal.
Before you can add any plants and fish, you need to make sure several things are completed.
Firstly, if the water is mildly chlorinated, allow it to stand for 48 hours before setting any plants in the water.
If you are going to add fish, you need to make sure that the water is dechlorinated first.
This can be done by using products such as Ammo Lock 2, which will neutralize the water, making it safe for the cold water fish.
If there was any dirt added into the water during the backfilling, it would probably be best to either fish out as much as possible, or simply drain and refill the water.
This is to ensure good pond health going forward, as well as making sure that the water at least starts from a clean state.
Finally, many people like to decorate around their pond, with either rocks or additional foliage.
This will hide the outer lip of the preformed mold, and conceal much of the sand and dirt used to backfill.
The addition of rocks make great homes for insects, such as woodlice, spiders, and waterborne flies, as well as improving the chances for healthy bacteria to form around the exterior of the pond, enhancing the pond’s ecosystem.
These not only improve the health of the pond, but the attraction of insects will also prove extra food for water creatures, such as common garden frogs, as well as particularly adventurous, and larger, breeds of fish.
Whilst this will be helped by the bacteria and algae that will take root in the pond, it is important to check the overall health and cleanliness from time to time.
If you have been cutting your grass, ensure that any stray clippings are removed from the water.
The same goes for any loose flower petals, branches, or shrub clippings which might have been blown into the water.
If you have fish, a good biofilter will help to ensure their health, and the cleanliness of the water.
This can also be improved with a “filter media”, the area where the bacteria can grow and thrive.
Traditionally this was achieved using gravel, but modern methods can include plastic coiling slices into sections, bioglass, aqua rocks, or Japanese filter mats, which are woven plastic sheets made from mixes of bonded fibers.
Once your pond is completed, you will be amazed at how calm and relaxing your garden can be.
With the attraction of helpful insects (such as bees and dragonflies), lush foliage, and decorative plants and rocks, it can make an excellent addition to any space.
And as an added incentive, the babbling sound of water created by the pond’s pump will add a sense of tranquility and peace to any garden.
The only thing left to do is give it a try. You won’t be disappointed!