How to Make a Pond Using a Flexible Liner
Credit: Opensource

Building your own DIY Koi pond with a flexible pond liner gives you the ability to customize your water feature. If you would like a larger sized pond, some stores carry large rolls that you can simply pull out and have it cut to your desired size by an employee. If not, you can special order it.

Flexible pond liners are typically made of polyethylene or synthetic rubber. The density of polyethylene can vary, but it is less expensive than the pre-molded pond shells you can buy in stores.

If there is a downside to using a liner it is that it can be susceptible to punctures if you are not careful. If that is a concern for you, you should look into other options for pond liners.

What is a koi pond?

The most critical decision of designing your own DIY pond with a flexible liner is deciding where to build it because will affect how much maintenance is involved in the future and if plants or fish will thrive in the environment.

You need to ask yourself some basic questions such what is the ultimate goal of the pond, how accessible should it be from your home and how it will be affected by the sun or wind.

Would you like the pond to be visible for the inside of the house through a window or from an outdoor deck area? Are you going to be growing live plants and creating a koi fishpond?

Furthermore, do you want this outdoor space to be a reclusive getaway from the main part of the backyard?

If so, do you have proper vegetation in a particular area to provide privacy?

Are you planning an elaborate waterfall or water feature?

If so, you need to make sure the area you choose is somewhat shielded from the wind by a privacy fence or adequate shrubbery to prevent the wind from evaporating the water in the pond at an increased rate.

Making a Site Plan

Before starting, it helps to draw your design to scale on grid paper using exact measurements.  

At some point before you begin the design, you need to check with any local codes to see if there are any restrictions on how far a pond can be set back from property lines.  If so, mark these as red lines around your property on your grid paper to ensure you do no go to close to the edge of your property line when you are building.

Also, you need to mark any utilities such as water, phone, cable lines and the location of a septic tank if applicable.

Begin making a site plan with grid paper using a scale of one quarter inch to 1 foot. Mark the northern direction on the paper then draw the property lines accordingly.

Next, mark any existing structures in the landscape area. If only a small portion of your yard is affected, just focus on that area on the grid. Mark any existing trees or shrubs. Next draw the exact size of the pond, garden or fountain to scale on the grid paper in the appropriate area.

This site plan can be as elaborate or as simple as you want, but it will give you an idea of the type of space you will have in between your new and existing structures and if modifications are needed before you begin.

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Sizing and Laying Out the Liner

Pond Underlayment

The first thing you need to do is clear the area of the site as designated by your site plan.

Outline the area of the pond on the ground using landscaper’s spray paint or simply using a water hose for the boundaries of an irregular shaped pond.

If your design will be square or rectangle, simply mark it with stakes and batter boards to identify the boundaries.  However, this is not a typical design since most people want their outdoor pond to look natural and nature does not follow lines.

Next, measure the overall width and length of the pond and determine the smallest measured rectangle that would enclose the pond. Basically you are measuring the maximum width and length that will enclose the pond in a rectangle.

Now you will need to estimate the amount of polyethylene liner will be needed. You do not need a pond calculator, just some basic math. Consider the measurements you just took and be sure to account for the pond depth.  In most municipalities, the maximum depth is 24 inches. 

Take the maximum depth, then double it and add that number to the width and length or the rectangular.

To allow for 12 inches of overlap, add an additional 24 inches to the width and length of the pond liner. So in all, you are adding 48 inches to the length and width of the maximum length and width of a rectangle you measured earlier.

How to Make a Pond - Preparing the Site

Now it is time to dig. First, you need to remove and save any existing sod so you can use it in other areas of your yard.  Use a flat head shovel to remove strips of sod within the area you have outlines, plus about 12 inches beyond the boundaries.  You may need to relay the pond outline if you removed it after measuring the area for the liner. Some people find that helpful, others find that it gets in their way when digging.

If your pond will have layers, or shelves, carefully dig the entire pond out to the level of those edges. Most shelves of this type for shallow water are about 12 inches assuming the deepest part of the pound will me around 24 inches. Then use a tamper or other heavy flat device to tamp down the soil.

Make sure your shelf is level using a 2x4, then proceed to digging the interior portion of the pond to a deeper depth. Make sure you check the depth regularly as you do not want to go deeper than code.

The sides of the pond should slope inward slightly dropping about 1 inch per foot toward the center.

At the lowest point of the pond, dig another hole about 6 to 12 inches deep to incorporate a sump hole for draining the pond if you desire.

Using a flat blade shovel, cut about a ledge about a foot wide around the pond rim for the edging material. Make sure you cut the ledge to a depth that accommodates the combined thickness of the edging material plus any underlayment materials, including any mortar bed you will be installing to hold rocks in place.

Also, keep in mind that any edging around a pond looks more natural if it slightly overhangs the pond by a few inches.

As you go along, always check the sides for level. If not, the pond itself will tell you once you fill it with water and you do not want that.

Before laying the liner, check the hole to make sure there is nothing in it that could possibly cut the liner. Then fill the bottom of the hole with sand to act as a cushion. Typically 2 to 3 inches is sufficient.

Small Pond Ideas - Installing the Pond Liner

Pond Liner

This entire project does not have to be done in one day. In fact, you definitely want to wait until you have good weather and the ground is relatively dry or you will be dealing with a muddy mess. If you cannot get all of this done in one day, relax, there is no rush.

On a warm sunny day, spread out the PVC liner to allow it to warm a bit so that it is more flexible and easier to handle.[2]

After about 15 minutes, drape the liner into the hole making sure it overlaps all sides of the hole. If you did your measurements correctly earlier, this will not be an issue.

Next, weigh down the edges of the liner with some heavy rocks to hold it in place. Tamp down as much of the liner inside the pond and make sure it follows the outline of your shelves as much as possible before beginning to fill it with water.

As you fill the liner with water, adjust it to conform to the sides of the ponds and smooth out as many creases as possible.

As the pond fills, remove some of the stones so that the liner does not stretch from the weight of the water and the weight of the stones holding it in place.[2]

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Finishing Up the Edges of the Pond

How to Make a Pond Using a Flexible Liner
Credit: Opensource

Now that the pond is full of water, cut off the excess edges of the lining using a heavy duty pair of scissors or yard cutters. However, leave enough around the rim and underneath the first course of edging stones you will apply later.

To keep the liner edges in place while you install edging, put nails through the liner into the ground for temporary support.[2]

Place coping stones around the edge of the pond as you desire. To prevent rock slides or people injuring themselves around the edges, you may want to mortar them in place.

Finally, if you placed your pond in a wooded area, you may want to lay a stone path leading to it.

Types of Pumps - DIY Pond Filter

How to Make a Pond Using a Flexible LinerCredit: OpensourceA pump for a pond is used to agitate the water for effect, for cleanliness or if you decided to install a water fall.

If you plan on having fish inside your pond, there are also requirements for keeping the water clean through filtration.

All of this is going to depend on the type of pond you decided to build and what you are going to use it for.

Pumps are sold in all varieties with varying pumping power based on how many gallons it will pump per hour. If you want a flowing water fall cascading into your pound, look for one with a strong pump as you will be bring water up from the bottom of the pond up 2 or 3 feet to allow it to flow downhill.[1]

Pumps are easy to install but they do require an electrical outlet so you will either need to have a new line run out to the pond area or bury an extension cord from an outlet outside your home.

In any event, follow the manufacturer’s recommendations for whatever pump you decide to buy.

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Final Thoughts

Flexible Pond Liners
Credit: mjpyro

In order to be satisfied with whatever type of pond or water garden you build, you need to analyze what is the purpose and how will it fit in with your existing landscape. If you do not take the time to do this upfront, you might end up with something that you never really planned initially.

I have known people that have pulled their ponds or fountains out of the ground after a couple of years because they simply did not plan anything out. They had no idea what they actually wanted and did no pre-planning. They just saw something in a home improvement store and bought it. Then without any real thought, they ended up with drainage and maintenance issues. The last thing you want to be doing is pulling leaves out of your pond every week because you did not think about the location in the beginning.

So take my advice and really ask yourself what you want an outdoor pond, do some research on your property, come up with an estimate and go from there. If you want to create a flexible design with maximum creativity, a flexible pond liner is a must.