HOW TO STOCK AND MAINTAIN A GARDEN POND

A garden pond can be left to its own devices as a miniature nature reserve, but will be a much more attractive feature if it is stocked with aquatic plants and ornamental fish.  Get the natural balance right and the pond will be virtually self-sustaining, needing only occasional attention to keep it is good condition. 

If you are stocking a new pond from scratch, get the plants established before introducing the fish. 

Always buy fish from a reputable source, to ensure that they are healthy to start with.

POND PLANTS

There are several distinct groups of plants you can grow in or around a garden pond.  These are the main ones:-

Oxygenators are essential plants for keeping the pond healthy.  Some are rooted, but most simply float in the water, absorbing carbon dioxide and releasing oxygen as they grow. Since they multiply fairly rapidly, start with a few small clumps and be prepared to cull the plants ruthlessly as they spread.   Simply hook out excess growth with a garden rake and put it on your compost heap.

Water Lilies are planted in containers that sit on the bottom of the pond and produce leaves and stunning flowers on the surface in the summer.  There are many different varieties.  Do not be tempted to over plant, they grow rapidly and can soon swamp a small pond.

Marginals are planted in containers set in shallow water on shelves around the pond margins.  This group includes various species of Iris, Flag, Marsh Marigold and the Arrow Head.

Floaters such as Fairy Moss, Greater Bladderwort and Water Soldier are flowering plants that simply float on the pond.  The Water Soldier sinks to the bottom in winter.

Marsh Plants, such as Bullrushes, can be planted at the edges of the pond, if the liner is extended and filled with soil to create waterlogged bog conditions.

Get specialist advise when choosing plants to suit your particular pond size, containers and special pH-balanced pond soil.  Do not be tempted to use ordinary garden soil, or to plant directly in soil spread on the bottom of the pond.

Golden Rule  - Always top pond plant containers with gravel to stop fish from disturbing the soil and therefore discolouring the water.

FISH FOR GARDEN PONDS

The humble Goldfish, bred by Chinese and Japanese fish-keepers from a dull brown wild species, is the most common fish kept in garden ponds.  The Goldfish family now has more than 100 varieties, including the Common Goldfish, the Comet with its long tail, the multi-coloured Shubunkins, the oval bodied Fantails and the Veiltails with their flowing fins.  Other species to look out for include the Oranda and the Lionhead.  Not all these are hardy enough to survive harsh winter conditions, the best survivors are the Common Goldfish, the Comet and the London Shubunkin.

Other species you could consider include Tench and Golden Orfe.   The former is a useful bottom feeder, scavenging food wasted by the other fish and so helping to keep the pond clean*.  The Golden Orfe with its gold and black markings, is by contrast, an active surface feeder and an excellent display fish.  However, it grows quite large so is not suitable for small ponds.

* I have been advised by Matt Williams of www.derbypondservices.co.uk that this is incorrect - as tench emit waste like any other fish, they do not help to keep ponds clean. Presumably, however, they do help to clear up any food dropping to the bottom of the pond.

If you have a larger pond you can consider keeping Koi.  These are an ornamental species of carp, much prized by the Japanese for their exotic colouring and marking.  They come in single colour, two colour and multi-coloured varieties, further distinguished by their scale development.

Always buy Koi only from a reputable source and make sure that your garden is secure.  Koi, especially large or well coloured specimens, are extremely valuable.

HOW MANY FISH?

To assess how many fish your pond will support, estimate its surface area and allow 60sq cm of surface for every 1 cm of fish (equivalent to 24 sq. inches per inch of fish).  Since fish grow and breed, it is best to start off with around one-third of the theoretical maximum number.  For example, a 1.8 x 1.2m (6ft x 4ft) pond will, in theory, support 360cm (144ins) of fish, equivalent to 36 individuals averaging 10cm (4ins)long, but, in practice, you should have only about 12.

Golden Rule - Your pond needs to have part of the area at least 60cm deep for goldfish and 1.5m or more for Koi if they are to be left over winter safely in the pond.

BUYING AND LOOKING AFTER FISH

Always buy fish from reputable established suppliers and check that all fish in their ponds or tanks appear healthy.

Transport fish home in partly-filled plastic bags placed in cardboard boxes in which the fish have enough depth to swim.

Float the bag in the pond for at least 30 minutes to allow the water temperatures to equalise before releasing the fish.

Don't overfeed fish; one meal every other day is enough in winter, increasing to twice a day in summer.  Use a feeding ring to confine the food to one spot and supply no more food than can be eaten in about ten minutes.

Pond fish can suffer from a range of ailments, including parasites, fungal infections and fin rot.  You can buy proprietary preparations to treat these, either in the pond or by catching and isolating affected fish in a small temporary 'hospital' pond.

Golden Rule - When you are creating a new pond, get the plants established and the water clear and balanced before introducing any fish.

LOOKING AFTER YOUR POND

The biggest enemies of your pond and its inhabitants are algae in summer, fallen leaves in autumn and ice in winter.

• To discourage algal growth, remove anything shading the water, especially overgrown water lilies and oxygenators.  Treat the water with a proprietary algicide.  Also see "Filters and Purifiers".
• In hot weather, top the pond up occasionally to replace water lost by evaporation.  If you have a fountain or waterfall, run it at intervals to help aerate the pond.
  
• Net the pond in Autumn to prevent leaves drifting into the water and decomposing, reducing the oxygen level.  Clear the netting of leaves at regular intervals.
  
• Place a small floating ball in the pond to keep part of the surface clear of ice during frosty weather, so that gases in the water can disperse.  Do not break ice by force, you may stun and injure the fish which will lie happily dormant in near-freezing temperatures.

FILTERS AND PURIFIERS

If you have a pump running a fountain or waterfall, you can fit a mechanical filter to the pump inlet to remove algae and other particles that cause cloudy 'green' water.  Alternatively, you can route the circulating water through a tank filter sited outside the pond;  this sieves out particles and also encourages the growth of bacteria that remove toxic waste.  Tank filters are best for larger ponds.

If algal pollution is a major problem and cannot be controlled by natural or chemical means, you could consider using a water purifier.  This treats water circulated through it with ultraviolet light, so effectively eliminating green water.

COPING WITH NATURE

Cats and dogs rarely cause trouble to a pond or its inhabitants and will often use the pond as a source of drinking water.  However, if you live in a rural area, herons are likely to be a major scourge, returning again and again to poach your fish.  The best way of deterring them is to string fine black cotton threads between pegs round the perimeter of the pond to snag their legs as they wade in.   

Frogs*, toads and possibly newts* will find their way to your pond quite naturally and will make it their home.  

If a population explosion threatens at spawning time, collect the excess frogs spawn and transfer it either to a permitting neighbour's pond or to natural country ponds (best to seek professional advice before undertaking this as it can spread disease).  Do not tip it down the drains.  If you have a pump in the pond remove all the spawn or it will block the filter inlet.

RUNNING REPAIRS

The main problem for any pond is springing a leak and mending one will mean draining the pond down to the level of the hole or tear so you can repair it.   If you have to drain the pond completely to make a repair first transfer the fish and plants to a temporary pond made by draping polythene sheeting inside dry laid brick walls.

• Patch holes in plastic or rubber liners with a proprietary pond patching kit.
  
• Mend cracks in pre-formed glass fibre ponds with a proprietary car body repair kit.
  
• Don't waste time trying to mend cracks in an old concrete-lined pond.   Drain it, clean it out and drape a new pond liner over the shell to make it waterproof again.

* Emma has written to emphasise that frogs/newts etc. will not cause fish any problems. The Great Crested Newt is a protected species and should NEVER be disturbed, so people should feel very privileged if they have these in their ponds.

Another thing to bear in mind is that some fish can eat tadpoles.

* Margaret comments "Newts may not harm fish, but fish will quickly eradicate newt eggs! If you have a wildlife pond, keep it that way and don't add fish!"

* Stuart comments as follows:-   Frogs can actually harm fish.  My mate had so many frogs returning back to his pond this year and with the water being cold the fish lay still for a lot of the time the frogs gripped onto them and where they took hold of the fish was over the gills. Thus the fish actually drowned as they could not function their breathing.  Just a word of advice - too many frogs or toads wiped his pond out of over 100 fish.