Floating and Submerged Aquatic Plants
Functional submerged plants
Submerged plants are essential in maintaining a balance within the garden pool. Although they are, by and large, unattractive and seldom selected on aesthetic grounds, it is, nevertheless, important to choose suitable varieties for the conditions that prevail. Certainly most require full sun if they are to flourish, but a number will tolerate a reasonable amount of shade and constantlytoo.
For a cool, shady situation few plants can equal Ceratophyllum demersum (hornwort) a dark green, bristly plant with long, spreading, tail-like growths. In America it is popularly called the coontail, an entirely appropriate and descriptive name. Unlike the majority of submerged aquatics it is not constantly rooted. As summer progresses it becomes free-floating, the stems towards the terminal buds thicken and eventually become detached and fall to the floor of the pool as turions. These remain dormant until the spring sunshine warms the water and stirs them into growth again.
In fact, the majority of submerged plants show little activity during the winter. Not even the fresh green Tillaea recurva with its hard, evergreen, cress-like foliage seems to stir itself. This is of little account, as during the winter algae activity is at its lowest ebb or non-existent. But come the first few warm days of spring, the water will quickly turn green, and this is when tillaea can play an important role. Unlike other submerged plants, which lose much of their foliage during the winter and have to regenerate it before growing actively, tillaea is there ready and waiting and as quick off the mark as any single-celled algae.
Isoetes lacustris (quillwort) will perform a similar function, but as it is more temperamental than tillaea it cannot be unreservedly recommended. Surprisingly a member of the fern family, this curious little plant has stout clumps of dark green, quill-like leaves which arise from a circular brown. Like most ferns and fern allies it prefers acid conditions.
So does Fontinalis antipyretica (willow moss), although this is by no means essential. An evergreen native with olive-green mossy foliage, this is one of the few submerged plants that enjoys turbulent or constantly.
Many submerged plants become more or less dormant during the winter, but retain a certain amount of foliage, although this may only serve to protect buds which will emerge the following year. Elodeas are good examples of this, particularly the widely grown Elodea canadensis (Canadian pondweed). With small curved leaves arranged in dense whorls around slender stems, it is probably one of the best known submerged plants. Certainly it is one of the most useful for the small pool owner as it rapidly carpets the floor or fills his containers with sheaves of luxuriant, dark green foliage. On past performance it has earned itself a reputation for being invasive, but this is of little account in the garden pool where excessive growth is easily removed.
About ten species of elodea are known to be in cultivation, but only E. canadensis is widely grown. The plant frequently offered by nurserymen as E. crispa is not, strictly speaking, an elodea at all, but Lagarosiphon major. This is the plant frequently sold by the pet trade for goldfish bowls. A dark green, crispy-leafed oxygenator with densely clothed stems that look almost snake-like in the water. Like E.canadensis this can grow vigorously in conditions to its liking, but is easily controlled and actually benefits from an occasional severeof over-exuberant growths.
Potomogetons are generally of more modest proportions, or, at least, those that can be recommended for the garden pool are. Never be tempted to introduce species with floating leaves like Potomogeton natans and P. lucens, for although extremely decorative when young, they rapidly outgrow their positions in a small pool. The only species that can be unreservedly recommended are the small-growing, totally submerged kinds like P. crispus (curled pondweed) P. acutifolius (sharp-leafed pondweed). The former is particularly desirable, for it has handsome, bronze-green, translucent leaves with crinkled and serrated margins, although P. acutifolius should not be neglected as it shares these virtues, but with leaves that are flat and entire.
Milfoils have delicate filigree foliage arranged on long, spire-like stems. These often terminate in tiny flower spikes which stand just clear of the water. Two species are popularly grown, Myriophyllum spicaturn and M. verticillatum. Both look superficially alike, except that the leaves of M. spicatum have a distinctive pinkish cast, whereas M. verticillatum is a clear bright green. For the goldfish fancier these two are indispensable, their delicate, feathery foliage being an ideal site for the deposition of spawn.
The callitriches are equally valuable to thekeeper. Their bright green, succulent, cress-like foliage providing the palatable green material so necessary for a balanced diet. Many species and forms find their way into garden ponds, but only Callitriche platycarpa (syn. C. verna) and C. hermaphroditica (syn. C. autumnalis) are offered by nurseries. These look very similar, except that C. platycarpa produces rosettes of narrowly elliptical floating leaves and dies down for the winter, while C. hermaphroditica is totally submerged but evergreen.
So is Eleocharis acicularis (hair grass) a real gem for the tub or sink garden. A close relative of the sedges, it produces spreading carpets of slender wiry foliage, which, once established, looks just like seedling grass. It seldom grows more than 8cm high and does not interfere with other plants nor become infested with algae. Unlike most other submerged aquatic plants, eleocharis does not lend itself to bunching and is, therefore, sold as tiny rooted clumps.