Do I need a biological filter for my garden pond?

Anglo Aquarium plant water garden at the Hampton Court Flower 2003, where they hoped to demonstrate a sustainable water garden where the plants are able to keep the water clear by being defended from the over inquisitive and semi-destructive koi carp by a hidden block wall.

If you (a) live in a warm country, (b) have small pools well stocked with fish, (c) prefer to see your fish than have masses of plant life in the pool, a biological filter system with an incorporated Ultra Violet Clarifier is pretty much essential. What should go on with those bacteria in the bottom of the pool in breaking down the waste and organic compounds in the water is essential to the well being of the whole pool. With a biological filtration system you have a turbo version of pool bottom at your control at the touch of a switch. Nowadays the filtration boxes have evolved into small systems working under pressure, which can be hidden out of sight at ground level and that can be serviced virtually by a twist of a lever.

A modern style pressure filter (with a cut-away to show its workings). Highly effective for its size, it reduces maintenance to at least a half, because it can be flushed out at the twist of a lever.

July is good for the late season marginal plants and the march of the bog brigade. And of course there are the lilies. Most of the real wet footed marginals have done their thing by now. There is still the big pickerel weed and purple loosestrife blazing away with the demur Flowering Rush all competing with the big grasses. In the bog there are the Ligularia, Astilbes and Hemerocallis or Day Lilies. Hostas are flowering and the Bistorts (Polygonums) are looking good. There are spectacular displays of Primula florindiae and P viallii and yellow loosestrife and soon there will be the Schizostylis to wind things up. Meanwhile variegated and yellow grasses keep up the brightness and Gunnera and Rheum palmatum (Ornamental Rhubarb) provide the big green backdrop. The Hampton Court Palace Flower show is the place to see these plants and how they can work in a damp garden, bog or water garden.

Pete Sims in his garden at the 2005 Hampton Court Flower Show managed to use many of the popular moisture loving and waterside plants like Hemerocallis, Astilbes and of course Primula florindiae.

What to look out for in July:

Leeches are getting pretty big and sassy at this time of year. So try to get a good look to see there arent any hanging off your fish. A very dilute salt bath will see them off if you cannot bear to screw them of.

If youve got a bog garden, make sure there none of those big weeds getting a foothold into it. Also make sure it is well watered. You ought to have a tube going right down into it thats perforated with holes. This helps watering in the hot and dry, getting the water down to the roots where it is needed.

Watering newly established bog gardens. Note the pipe at the back can be used to water the plants right down to the bottom of their roots once they plants get established.

NOW is the time to thin out those oxygenators if they are getting out of hand. Not in Autumn and not in Spring.

Plants that need a good long growing season to get going can be sown from now on. Some experts recommend that it is time to sow the seed of Tetragona waterlilies. It would also be a good time to sow the likes of Marsh Marigolds (Caltha palustris) or Ragged Robin (Lychnis flos-cuculi).

Sow seed of plants that need a head start for spring flowering now. They can be sown thinly on the surface of damp compost in a small pot or tray and cover with a thin layer of compost. Place this in a larger watertight container half full of water and cover with a plastic bag to retain the moisture. The bag can be supported by stiff wire in the pot. Both can removed after germination. This was a sowing of watercress that can be started at any time in the growing season.

If it looks as though there are small fish that may get eaten, rescue them. Keep them in a tank and feed them up until theyre bigger.

And if you are going on holiday and you were going to get the neighbours to feed the fish while you were away. Dont. Let the fish starve for a week or two. It will do them good. Unless your neighbours are experienced and successful fish keepers they will always overfeed for fear of underfeeding. The result will be disease and algae and God knows what. Leave it to God. He organises nice fat flies and things for this time of year.