Active and Passive Bogs

by: Demi Fortuna

Installation of perimeter bogs is simple when building a new pond; just widen the flat rock shelf you’re putting your coping or edge stones on as far back as you have excess liner, and make sure the liner is secured higher than water level at the outer edge of the bog.

The 8” depth of the RSVP Rock Shelf is a perfect depth for a shallow gravel bed that will be easy to clean if ever necessary. The size of the bog or bogs should be at least 10% of the total surface area of the pond, up to 30% if you plan on a lot of fish, and will be easiest to maintain if they run along the edge of the pond without being very wide, maybe 1-3 feet.

A Passive Bog simply allows the pond water to flow into the gravel bed unassisted. Water will seep through the coping rocks into the gravel. To really supercharge nitrate removal, consider installing an Active Bog.

The ‘active’ part refers to running water forced through the gravel, which brings nutrients constantly and directly into the root systems of whatever is planted in the Bog. Typically, this is accomplished by placing a perforated pipe under the gravel and feeding 500-1000 gph into the base of the gravel bed. Not only will the nitrates be removed, fine particles will also be trapped, polishing the water as well or better than mechanical filters, and there are no pads to clean. Simply compost the excess plant material at the end of the season.