Water garden calendar, November

In the UK, normally the season of mellow fruitfulness is over and the feeling and look of a grey blanket settles over everything. A hot summer and a rapid temperature change produces a spectacular autumn display of colour. With the oncoming cold, the pools, ponds and water gardens will have definitely gone to sleep. So if the water has cooled below 7C, dont feed your fish, especially the Koi; between 7 and 10C only feed your Koi either wheat germ or some other top quality winter feed.

Many people who have tall grassy plants around the pool and who havent cut them back are congratulating themselves because there is still cover for the wildlife that is still moving in and out of the pool, unable to settle down, but also it looks very good. In a dry year the likes of Cyperus longus, Sweet Galingale and the indigenous species of Carex or sedges produce quite an autumnal blaze. Meanwhile the scented rush, Acorus calamus and its tufty variegated cousin Acorus gramineus stay evergreen, so leave them and the sedges like Carex Bowles Golden unless they are looking particularly sorry for themselves.

Now assuming that November does produce unseasonally mild weather, we should be thinking in terms of the normal routine of cleaning out pumps, and in cold districts, removing the pumps altogether to store them away indoors. If there is a biological filter, the filter pump should be repositioned onto the marginal shelf so that just the top few inches of water are being turned over, rather than mixing up the whole lot. As water gets to around 4C, it becomes its most dense and sinks to the bottom of the pool. Fish are quite content to live down in this water that is oxygen rich. If the water were to get any colder it would rise up in the pool (contrary to any physical behaviour of any other liquid or even water at higher temperatures) and as it approached the magical 0C it would turn into the solid that we know as ice. This naturally enough is not to fishes liking. So, if we are turning over the whole volume of the pool through a filter or waterfall and the cool extremes at the surface, we would find the whole system cooling down like refrigerator, down to the temperatures at the surface. So try to keep the lower reaches of the pool undisturbed.

As things get colder, the biological filter is operating less and less on a biological level. If conditions freeze then the filter needs to be stopped. When things warm up, and you turn the filter back on, it will be like a two slug Russian Roulette as to whether it will or will not deposit toxic filth into the pond, and at a time when it least can cope. So the best bet here is to clean it out now. Clean out the filth in the bottom with rain or pool water and rinse out the sponges and the filter medium. If you have an ultra violet clarifier that is easily detached, bring that in or make sure it is empty of water.

If the pool does ice over, dont break the ice with a hammer. This knocks the fish senseless. Two or three days ice wont do the fish any harm. If however there is a lot of muck in the bottom of the pool and there may be a build up of noxious gases in this time, sit a pan of hot water on top of surface until it melts a nice hole. The technological solutions is a small pool heater that is like a small warm rod on a polystyrene float that just heats enough water around it to maintain a small hole in the ice.

Gas bubbles building up underneath the ice could be a bad sign if you know there is a lot of rotting detritus in the bottom of the pond.

This will enable any build up of gas to be released. It will also relieve the stress the ice may be causing on the fabric of the pool liner or its structure. These are the two reasons many people float something soft and rubbery in the pool as a guard against mild freezing.

Over twenty years ago, a friend of mine called Charles Maplethorpe invented a device that was a ring of polystyrene that held a small round aquatic plant basket of pebbles in the centre. The pebbles were half submerged and cocooned in the insulating polystyrene float that formed a frost-free link with the water and the outside air. This worked right down to surprisingly low temperatures and sold in the thousands for years until it lost its credibility one year of extremes temperatures when pools froze solid.

If it does get really cold, take Lobelia cardinalis under cover. By the way, if youve invested in any slightly exotic plants like Cannas or floaters like Eichornia crassipes Water Hyacinth (for those of you in the US and SA- Yep! They actually grow them on purpose in the UK.) and Pistia stratiotes, Water Lettuce, take them into a frost free greenhouse and grow them in a tray. Try to maintain the temperature above 4C

Water Hyacinth can actually be planted up in a pot to make it more winter hardy.

Plants flowering at this time of year? The hardy South African Aponogeton distachyos- the water hawthorn, and in the bog the other plant from around there, Schizostylis coccinea, once commonly referred to as the Kaffir Lily, now it is considered more politically correct to refer to it as the River Lily. It is a fantastic show at any time of year, let alone blazing away in the dull washed-out blear of the sad grey English garden in winter. keep yourself warm and dry.