Marginal Plants: Aquatic Plants for the Garden Pond
Harbingers of spring
Although most aquatic plants lie low until the lengthening days of early summer, there are a few hardy characters that will withstand the chill breezes of spring to brighten up the poolside and give a taste of what is to come.
Marsh marigolds are the first to show their faces, especially Caltha palustris (kingcup) smothered in single blossoms of glistening gold. An adaptable plant, this will grow in anything from moistto 20cm of water, but always makes a more compact plant in shallow conditions. A not uncommon native, this starts flowering as early as March and will usually continue until May. Even when not in flower it is quite attractive, forming neat rounded hummocks of dark green foliage.
Its double form Caltha palustris ‘Fiore Pleno’ is even more compact, with bright golden, waxylike miniature pompon which completely obscure its bold, dark green foliage. The single white form Caltha palustris alba is not so inspiring and much overrated by both nurserymen and the media. It is true that when well grown it looks very nice. However, to grow it properly requires constant vigilance, for it is prone to and in a very short time becomes stunted and distorted. Why this should be is difficult to say, for if other caltha species and varieties are grown close by they are seldom affected.
Those who require a really good white marsh marigold need look no further than Caltha leptosepala (mountain marigold). This has expansive blooms with just a hint of silver and splendid rich green foliage. It is somewhat larger than Caltha palustris alba, and its variety grandiflora is really quite huge.
The giant of the family though is Caltha polypetala (Himalayan marsh marigold). Frequently attaining a height of 90cm with immense leaves 25cm across and great bunches of golden blossoms, this is a magnificent subject for the larger pool. It can be grown successfully in the smaller water garden, but its considerable stature and brightly coloured flowers tend to be rather overwhelming.
As they start flowering at least a month before anything else, we tend to regard calthas as spot or specimen plants, but I get a splendid effect by associating the shorter growing kinds with Myosotis scorpioides (water forget-me-not). This moisture-loving relative of that much-loved inhabitant of old cottage gardens does not flower until the calthas are almost over, but its slender, scrambling foliage gains from the body given to it by the bold, scalloped leaves of its neighbour and, in turn, disguises the latter’s untidy basal growth. An added bonus comes in a late spring when the marsh marigold is a little retarded, for then both erupt at the same time. The bright waxy blossoms of the calthas rising out of dark leaves with the starry, ultramarine flowers of myosotis sparkling between. Even in a normal season the final fling of the caltha will coincide with the first flush of forget-me-not blossom. These are not to be despised when grown alone, for they are freely produced and create an attractive blue haze for much of the summer.
Menyanthes trifoliata (bog bean) can be associated with myosotis in a similar manner, but with less startling results. In fact, I think that menyanthes should always be grown amongst clump-forming plants as it is a rather untidy sprawling character that leaves areas of the marginal shelves devoid of foliage. This is its only short-coming, for the stark, broad bean-like leaves create valuable contrasts amongst plants which are for the most part grass-like. Although looking like a bean it is not a legume, a fact that is confirmed during April and May when it thrusts up dense clusters of quaint white or pinkish fringed blossoms.
Calla palustris (bog arum) grows in precisely the same manner as menyanthes, spreading by means of thick green creeping rhizomes. Fortunately, these are clothed more liberally with foliage and it is thus an excellent plant for disguising the harsh edge of the pool. Its dark green, heart-shaped leaves are bold and glossy, and during late spring and early summer become littered with tiny white papery spathes not unlike those of the florist’s arum. However, this is not its main attraction, for these are followed during autumn by stout spikes of striking red berries.
Lysichitums (skunk cabbages) belong to the arum family as well, but are grown for their immense spathes which are produced during April well in advance of their foliage. In the North American Lysichitum americanum they are bright yellow and of a thick parchment-like texture, while those of the Asiatic Lysichitum camtschatcense are pure white and almost translucent. Both produce large clumps of bright green, cabbagy leaves which are of considerable architectural merit.