Treat marginals growing in the soil surrounding the pool as any other herbaceous. With regard to those aquatic plants growing in the water area, if you have stocked and planted up your pond as suggested, maintenance need only consist of an annual spring clean sometime during April, May or June. Remove the crates, pull off dead material and clean out all debris which has accumulated at the bottom.
After a few years, the plants in the crates will become overcrowded and need to be divided and replanted as before in fresh soil. This is the best method of propagation.
Most ponds will develop blanket weed at some time or another. There is not much you can do about it other than remove it manually. If you just twirl a stick around in the water you can attach a lot of it to the end of the stick — rather like candyfloss — and if you do this regularly (several times a week sometimes in summer as it spreads rapidly in warm weather) you will generally manage to keep on top of it. However, as the pool surface becomes covered with lily and other flat leaves, light will gradually be excluded and it will eventually be greatly reduced.
You will have to keep your eye on the pool in autumn to make sure large quantities of leaves do not fall in. These gradually sink to the bottom and rot, giving off poisonous gases and polluting the water. It pays to cover the pond with fine mesh netting if you do find a lot of leaves blowing into it — you can remove the cover when the leaves have stopped coming down.