Water Lilies: any diseased or mottled leaves of retiring water lilies should be given a gentle tug to part them from the parent water lilies tuber before they sink to rot below.

I am grateful to Peter J May for the information. You can also access his full article on preparing a pond and garden pond plants for winter here. This article was written for the northern hemisphere - remember this wherever dates are mentioned.

Handling and treatment of different pond plants

Floating garden pond plants ... like Water Lettuce (Pistia stratiotes)  and Water Hyacinth (Eichornia crassipes)  must be taken indoors and kept in light frost-free shade. Water Hyacinth can be potted up into a light, merely moist compost. Water Soldier (Stratiotes aloides)  will sink to the bottom before the first frosts whereas Frogbit (Hydrocharis morsus-ranae ) and Water Chestnut (Trapa natans) form nuts or buds that sink to the bottom to rise again the following year to form plantlets. Unfortunately the Frogbit will fall prey to predatory snails and the Water Chestnut is unlikely to form nuts in our climate, so they need rescuing to a pan of muddy water in good time before the party is over, so they can do their thing in the warm protective ambience of a greenhouse or light shed.

• Pioneering marginals ... of the garden pond plants world like Bog Bean (Menyanthes trifoliata), the Spearworts (Ranunculus flammula and R. lingua’ Grandiflora)  and Parrots Feather (Myriophyllum aquaticum syn. proserpinacoides) that seem intent on investigating the outer reaches of their universe should be cut back to home base: show these garden pond plants what you’re made of.  The same goes for those garden pond plants like Hell’s Angels of the pond margins, the Reed Maces ( Typha angustifolia and Typha latifolia), and any of those suspect ‘Reedy’, ‘Rushy’ looking garden pond plants things that don’t seem to do much, apart from grow. Feel around the baskets to see which plants have linked up in a firm vegetative bond. A bit of basket busting may be in order to sort them out. If the problem is not too bad, you can leave that little nightmare until spring.
• Tender marginals ... Garden pond plants need to be removed wholesale. Canna lilies can be potted up and plunged into a bed in cold frames, otherwise keep these garden pond plants cool but frost free and dry along with all the other exotics you have been tempted buy over the last few months. Once upon a time Arum lilies (Zantedeschia aethiopica ‘Crowborough’ ) and Lobelia cardinalis  were treated with the same respect, but now our winters seem quite bearable to them. The more exotic looking yellow and spotty leafed Zantedeschia elliotiana , Z. pentlandii  or the pink tinged Z. rehmannii should have been dried out since mid-July. Store these garden pond plants under greenhouse staging well above freezing. Bring them to life again in February.  

• Any exotics like Canna hybrids lilies should have been removed at the end of September, and planted in ordinary compost and kept in a frost-free green house. Arum Lilies can either be settled deep in the pool or alternatively over wintered in pots in a greenhouse. Gone are the days when we would ‘plunge’ the pots into clinker beds in cold frames along with the dark leaved Lobelia cardinalis in trays. With the current spate of mild winters in the south, gardeners find that as long as the plants are in large enough groups, they survive quite happily outside.

   Some of the thin sword shaped leaved rushes and reeds will still seem very much in their element, perhaps acquiring attractive russets that subtly flash changes as the autumn winds rock the swathes of plants en masse. It is always a dilemma in cutting these back, as the movement from these grassy plants lends life to a scene that is otherwise dormant.

  For small water gardens it perhaps wiser to at least cut off the seed heads before they shed, since all these marsh reeds and rushes carry an armoury of seed to perpetuate their species, scattering them on the wind to all four corners of your water world.

  In the water garden that is a wildlife haven, the remaining standing leaves will keep a cover for the ingress and exit of insomniac amphibians and thirsty mammals, but unfortunately will also serve as hide for herons. If you have to net your pond against the autumn fall, cut them back to one third. The net will then double as a heron deterrent.

  Water Chestnut (Trapa natans), This dies back to leave spiny edible fruits, if it has been a good summer. Do not let them dry out at any time. They should be sown in pans of loam underwater from April-May. Heat to 18-21c until germination then grow them unheated. But don’t let the temperature drop below 7°c.

  
  Water Lettuce (Pistia stratiotes) If there are any off shoots, separate them from the parent plant and float in shallow water at above 7°c.

  Water Hyacinth (Eichornia crassipes) South Africans and Florida folk are amazed we should want to preserve this plant, but it has a beautiful flower and will help to keep algae at bay. It can be planted into loam or compost in a frost-free greenhouse. Alternatively float in shallow trays of water. Over winter at over 10°c.

  Fairy Moss (Azolla  filiculoides) This succumbs to hard winter frosts, when it turns bright red before disappearing. Many people would be glad to see the end of it in their pools, but if you want to overwinter it, it should be easy enough in a bucket in any frost free, light environment.

  The waterlilies, if they are still struggling on through October, their leaves will be looking diseased and mottled. If you can reach any of the worst leaves, give them a gentle tug to rescue them from rotting in the bottom the pool.  Every little helps in preventing the build of detritus in the bottom of the pool. The lilies themselves want as little disturbance as possible until late spring.