Yearly maintenance activities, such as the removal of thread algae, Lemna and detritus, in addition to periodical dredging, keep ponds and waterways and their vegetations in reasonable shape. One must, however, be very careful. Reducing vigorous, abundant populations of Stratiotes aloides, Menyanthes trifoliata, Calla palustris or Potentilla palustris may cause a sudden decrease in vitality or even their complete disappearance. The subtle balance of such vegetation appears to be easily disrupted. A gradual development and seemingly unrestrained proliferation over a period of years may deflate when it is interfered with unwisely, never to regain its previous vigour.
Banks and pond edges
Banks and pond edges are the preferred sites for species of moist and wet soils. Many marsh and bank plants are among the most beautiful and free-flowering of the wild flora: Caltha palustris, Leucojum aestivum, Iris pseudacorus, Filipendula ulmaria and Lythrum salicaria create spectacular combinations, as do Valeriana officinalis, Euphorbia palustris, Osmunda regalis, Senecio paludosus and S. fluviatilis, and Eupatorium cannabinum. Whether planted as individual species or in combinations, they offer many opportunities. In very wet soil or shallow water (i. e. with waterlevels up to 10cm, or with the water table up to 30cm below soil level), one may create transitional vegetation between land and water. Species such as Caltha palustris, Veronica beccabunga, Calla palustris, Thelyptera palustris and Potentilla palustris are excellently suited for this purpose. Additional species include Alisma plantagoaquatica and A. lanceolata, Gratiola officinalis and Myosotis palustris. The latter should be used with caution., since it may spread quickly through seeding and the rooting of loose stems. Galium palustre and G. uliginosum, with their lacey, romantic flowers, may lend a very nice, airy effect to marsh vegetations, but one should take care! They do not look like it, but they may grow rampant, self-seeding profusely and their roots, thin as gossamer, colonising mosses and all other kinds of other plants. Once they have thus established themselves, they become almost impossible to restrain or weed out. The fine roots break off easily, making it easy for the plants to regrow into flowering, seeding plants. Rampant growth is the reason for caution in the use of species like Mentha and Scutellaria galericulata as well. If one can provide them with a spot of their own—where they may proliferate without causing trouble—they may certainly be applied. If not, one does better to apply it only in vegetation subjected to a mowing regime.