Vegetable filters or mini reed bed systems

What is a vegetable filter?

The principle of the Reed Bed system or vegetable filtration was a part of a sophisticated garden design at the Chelsea Flower Show 2002. The garden was called Clearwater, designed by Mark Walker and Sarah Wiggles worth. So what relevance does this have to the ordinary garden owner or pond keeper?

Solar cells apparently driving pumps that pump domestic grey water (water that has been used for washing) to the top of the reed bed system. By the time it reached the bottom it should be clean.

It is mid-summer; the fish in your pool are really active, they are healthy and growing, you are feeding them everyday and the sun is out and everything should be just koitastic. But it aint. You know the fish are there, but the water is so green the best you see are ghostly green shadows at feeding time with a flash of whiskery jaws. You know what the problem is, it is nitrates, not harmful to the fish, but it causes the algae to proliferate so much your filter and U/V system cant keep it clear. After all the algae are bound to multiply. They are plants and nitrates are pure rocket fuel for plants.

So would it not be not only logical but also biological to get plants on your side in there in the water to be munching up the nitrates before them bleepin algae get to them? Yes it would. All you need to do is call in what they call higher plants, which are basically plants that are bit more sophisticated than your average algae and preferably more greedy, and with greed comes vegetable muscle. Now when we are talking muscle in the plant world, the best crew for dealing with this situation are not the sort you want to have direct access to the pond, because they would undoubtedly take over and you would have a worse problem than the algae. It would be like inviting the local chapter of the Hells Angels for a drink at your sophisticated soiree; you would be asking for trouble. You need these guys as bouncers at the door! And so let it be with the heavy weights of the water garden. These are essentially plants that grow fast, so have them nicely confined in a container and let the fluid contents of the pool flow through their roots systems. Working in conjunction with the normal micro flora you find round the root hairs and in the bottom of ponds, a lot of those undesirable nitrates will be just taken out of the water and absorbed by the plants.

Not only that, any soluble toxins or pollutants will be extracted. Factories, mines and breweries have all taken advantage of using this capability of plants. All human waste, tin, lead and even radioactive uranium can be extracted from water as long as the root hairs of these plants have access to the water. In large domestic situations and controlled industrial applications, using plants in this way, they are referred to as reed bed systems and for a pond or pool Im calling it a vegetable filter.

The huge tank of reeds processing the human and kitchen wastewater at the HDRA gardens at Ryton. The cleaned water runs over into the pond.

If you are going to use Phragmites australis or the common reed or Norfolk reed in a filter bed try to stop it seeding. It is liable to get everywhere.

The common reed or Norfolk reed, Phragmites australis, is the top performer in these filters, because not only has it got a phenomenal growth rate in the right conditions, but also obligingly oxygenates the water as well; essential for many of the bacteria that need oxygen to sustain them. Other plants that do well in my books are Water Cress, Rorippa nasturtium-aquaticum, although it succumbs in very polluted water, Bittercress or Cardamine praetense and Fools Water Cress, Apium nodiflorum, which loves alkaline water.

Water cress: Rorippa nasturtium-aqauticum.

Apium nodiflorum; the rampant root run is revealed, sprouting at virtually every leaf node.

Is it easy to add to my set up?

If you already have a stream, or waterfalls with header pools, you can place aquatic baskets planted up with cress or reeds in strategic places. In fact any plants that are easy to keep in order will help. Keep an eye on them in order to stop them from seeding or running adventitious shoots under your rockwork. A regular cut back ensures they are kept working producing new growth most of the season.

In this header pool to the waterfall I planted Villarsia, Nymphoides peltata, a useful vegetable filter.

You can just about see the clarity of the water in the pool . N.B. The heron trip wires.

If you have a relatively small pool and you would like to buy a proprietary product off the shelf in kit form with everything you need, then there is the Oase Filto-Fall, which is a basic kit for processing the water in a 2 cubic metre pool. All it needs to work is a pump capable of handling the conditions you will put it in (see Add on the Mechanics later) that will turn over 5000 litres per hour, which needs a power supply and hose, and of course half a dozen clumps of Norfolk reed.

Oase Filto-Fall . It is designed to sit embedded into the ground on the edge of a pool or at the top of waterfall or stream. Water pumped up from the pool will enter at the front base of the tank (note the hole for a fitting in the bottom/front) and rise up through the plants and cascade into the header pool. Because it rises up in the tank from pressure from the pump, it could not be incorporated in an existing filter system unless it was of the pressure type like the Hozelock Bioforce or the Oase Filtoclear filters. This will cost you at the time of writing in the region of 50 or 60 but will only effectively process 2cubic metres of pond water.