pond marginal planting pockets

construction note no.5006

Aquatic plants are the most vital element of any water garden or pond, yet are often treated as an afterthought. Planting areas need to be built into the very design and contruction of the pond. This is especially important as insufficient use of plants is probably the biggest cause of unclear water (along with overstocking of fish).

Marginal shelves built into the side of a pond are traditionally used to sit baskets on - but these are not so good as a shelf filled with soil, even in the smallest of ponds. The only exception to this rule is when you really want to grow one of the most aggresive species, which will fill and soon choke up a smaller planting pocket Once choked in a confined space, they can then prove very difficult to remove. You have to choose your species carefully and that will be the subject of a future Plant Note.

The beauty of a good marginal planting pocket is that the soil appears to just slope straight down under the water, giving a very natural planting effect and hiding all signs of the liner. It also gives a range of soil heights, from above water level to several inches/cm under. This increases the range of plants that can be used, maximising biodiversity.

Construction method:

1. When excavating the pond, cut wide marginal shelves of 500 - 1000 mm wide out, to a depth that will be 300 - 400 mm below the final water level (allow for concrete pad on shelf).
2. Lay the sand and felt-liner-felt layers down as described in 5002: pond lining. Fold liner neatly int curves and corners, minimising creases
3. Once whole liner is in place, trim down excess to 200 - 300 mm above final water level. Cut a horizontal ledge as far above the water level as needed and lay liner over. Replace soil over liner. Note: there are many ways of dealing with the back edge, depending upon what's happening outside of the pond. These will be covered in another design note.
4. Place a concrete pad 50-70 mm thickon the chelf and up the sloped back face of the liner to above water level (but not so that it will show above the soil). This should end at the same point that the liner has been tucked into the bank.
5. Once concrete pad has set, a retaining edge needs to be built along the edge to retain the soil on the shelf. Usually this will be from rocks or logs, set in with mortar. They can be to a finished height below, or above, water level, depending on circumstance.
6. Backfill the shelf with a poor soil - subsoil from the pond would be ideal Note that “aquatic soil” obtainable from garden centres is really just subsoil - ie it is nutrient and humus poor. If this is contaminated or very stoney, sieve or replace. Slope the soil up to the back of the shelf to meet the existing ground level.
7. Plant up the marginals either before or after the pond has been filled. A gravel mulch can be placed on the soil if desired.

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