In our recent blog posts we have been discussing ways to have a beautiful water garden while also helping the environment by utilizing sustainability tactics and reducing our carbon footprint. Another way to be kind to our planet is by using bog garden filtration, which turns waste into a resource. The benefits of bog garden filtration are clear water and low maintenance. It creates an ecosystem that maximizes the breakdown of organic matter and nutrient absorption, stunts the growth of algae in the pond, and keeps the water looking gorgeous!
Bog filters are extremely effective at removing nutrients from the pond water. This process is achieved by pumping pond water evenly through a gravel bed via a grid of perforated PVC pipework. The gravel offers a surface area for nitrifying bacteria to colonize. The bacteria reduce fish and plant waste and turn it into plant food, which is consumed by bog plants growing in the gravel. The water is returned to the pond stripped of all nutrients, thereby preventing the algae from forming and multiplying.
Here is a quick way to construct a bog gravel filter in your water garden:
- Excavate an area: Find an area next to the main pond you’d like to place your bog filter and excavate it to a depth of 12-14".
- Install a liner: Place the liner in your pond and bog filter, following the liner installation instructions. For decorative purposes, hide all liner after construction.
- Create a partition: The filter is within the pond, separated by a porous retaining wall, commonly made up of concrete or concrete blocks. The top of the wall should be 1-2" below the pond surface when filled. Remember to make the wall for the bog filter level, and to allow extra liner for the sides of the retaining wall.
- Make sure the filter is raised: The filter is built next to and higher than the pond; water flows back via a stream or waterfall.
- Create a border: A ledge, 12 inches deep and as wide as it needs to be, is constructed around the perimeter of the pond. At the edge of the ledge a porous wall is built to retain the gravel. If you’d like an island, build a porous retaining wall on all sides in the middle of the pond. You can use decorative rocks to use for aesthetic purposes. You can also place the bog filter across from where people normally view the pond as it provides a beautiful background for the water garden.
- Pump installation: Install the pump in the pond as far away from the bog filter as possible, using a pump which circulates pond water at least once every two hours for ponds under 4,000 gallons, and at least once every four hours for ponds over 4,000 gallons (the more the better).
- Piping: Use PVC pipe to build a distribution manifold the length of the bog.
- Gravel: Fill bog filter with 3/8” diameter rounded pea gravel, mounding the gravel so it is 2” to 3" above water level for most of the bog. Most gravel is not very clean. Wash it as best you can before adding to the filter, but be aware it will muddy or cloud up the pond. The filter will clear that up very shortly.
- Planting: There are two main categories of moisture loving plants; tall plants with persistent fibrous roots and short “ground cover” plants. The tall plants provide great sites for colonization for beneficial microbes in summer and winter. Some examples are various rushes, Thalia, Iris psuedacorus, Iris versicolor, and cannas. You can also use cattails, pickerel, Louisiana iris, lizard’s tail, ribbon grass, horsetail, hostas, and daylilies. The short “ground cover” plants will look nice around the edge of the bog and among the tall plants. Some fast growing kinds are parrot’s feather and creeping Jenny and if you’d like to incorporate some edible plants you can use variegated or green water celery and aquatic mint. There are also shade-loving plants like aquatic forget-me-not and watercress. These fast growers provide the majority of the nutrient absorption and soften the transition between pond and land. Be sure not to over populate as it can stunt growth, which affects absorption, and also can look untidy.
- Culture your water: At first it is a good idea to inoculate the pond with a pond bacterial culture, like pond cleaner tablets. This can help with a new pond, or if the pond accumulates organic debris quickly, but should not normally be needed.
- Pottery Bog: Get creative with your bog filter! You can create a filter from decorative pottery, barrels, convert a waterfall filter, or other household items. Pottery bog filters are great for small ponds or additional filtration for larger ponds!
- Maintenance: The best part about bog filters is they are low maintenance! It entails just some trimming of dead foliage in fall and harvesting extra plant material.
Get started setting up your bog garden filtration system! You will not only be helping the environment, but with the low maintenance you will be beautifully decorating your pond while ridding it of the dreaded algae. All you’ll be left with is gorgeous crystal clear water all season long.