When is the best time to clean out ponds, and is it OK to do it thoroughly just once every 5 years?
It is very difficult to give precise advise about when it is best to manage ponds as every pond is different. A precautionary approach is by far the best approach ecologically speaking and the cheapest.
For the purpose of nature conservation ponds often need no management, people just think they do because the pond does not "look" good (whatever that means)! Pond ecology has been very poorly understood until relatively recently and still is by many people.All ponds are different and however shady, small, shallow or temporary can and do support life. Often these funny look ponds support the rarer, and more interesting species and communities - but are easily overlooked and damaged to produce the perfect (to modern humans) looking pond.
At Pond Conservation (the only organisation to have carried out systematic research into the ecology of pond) our general advise is to manage when everything is least active i.e. Novemeber to January. This way you are less likely to disturb the things living in the pond.
Ideally managment should only be carried out after proper survey work has been undertaken identifying what the pond is like and what lives in / is using it. Usually this does not happen but management is done in a formulaeic and damaging manner, based on a series of myths that have grown up over many generations e.g. drying out is not bad or damaging (some of the best nature conservation ponds are those dry out on a regular basis), large amounts of vegetation in a pond is good (open water much loved by people is a hostile difficult place to live for most aquatic creatures), water does not need to be deep (shallow is better being warmer and more biologically productive), shading is not bad either (shady ponds can have less problems with invasive plants such as Duckweed as it is cooler), trees growing in and around ponds are perfectly natural and provide an incredible variety of habitat niches (many of the original ponds before man came along and started to manage the landscape would have been in woodlands or places heavily shaded by trees) ....... The simple rule to remember is that before before we came along and started to worry wildife was getting on with it in all manner of ponds and adapting to every possible variation we can imagine (and more).
If there is a genuine specific problem that needs management then this general rule may be no good. For instance the colonisation of a pond by one of the foreign invasive water weeds is best tackled by its removal as it is growing and normally this is impossible to do in the winter months since it will either be much reduced or have entirely died back.
So, in summary first define if there is actually any need to manage, what is the actual problem and what is the solution(s). Even having done this little work may be required and the work could be staggered over several task days in year or over a period of years (depending on the problem and circumstances). Use the method and timing that creates as little disturbance as possible, especially in spring and summer months. This is a much better approach as heavy or invasive management (any management come to that) can and often has unexpected and undesirable consequences (which may be worse and more intractible than the original "problem").
Check out the Pond Conservation website for information, including some leaflets to download and a flier for a book explaining all about real rather than mythical pond ecology, pond management, creation etc. etc.
Finally a few pieces of general advice:
If you can create new ponds, often this is better than worrying about existing ponds.
Water quailty is more important than quantity. Site new ponds in areas of clean water e.g. not on potentially or actually polluted or enriched water fed ditches but off line. They may have less water but they will be better ponds.
Looking after the surrounds is as important as the pond itself. An unmanaged or unintensively managed (undisturbed) pond surround will be better for wildlife and act as good buffer soaking up pollutants and reducing untoward effects of intensive management on land closeby.
Ponds do not normally need cleaning out regularly, at any time of year.
We vare very intersted in finding out about where ponds are and what lives in them. Get in touch if you would like to help us, we can supply a simple recording form which is also available form the National Pond Monitoring Network website (linked to the Pond Conservation site).
As Ponds officer for Oxfordshire I am keen to help wherever I can. My time is limited but ypu can but ask, even it is only a bit of informal verbal advice ...
Rod d'Ayala, Ponds Officer for Pond Conservation, based at Oxford Brookes University