Some of the most interesting and ornamental of all plants grow in water and in wet places. It is possible to make an aquatic flower-garden, and also to use water and bog plants as a part of the landscape work.
The essential consideration in the growing of aquatics is the making of the pond. It is possible to grow water-lilies in tubs and half barrels; but this does not provide sufficient room, and the plant-food is likely soon to be exhausted and the plants to fail. The small quantity of water is likely also to become foul.
The best ponds are those made by good mason work, for the water does not become muddy by working among the plants. In cement ponds it is best to plant the roots of water-lilies in shallow boxes of earth (1 foot deep and 3 or 4 feet square), or to hold the earth in mason-work compartments.
[Illustration X: A shallow lawn pond, containing water-lilies, variegated sweet flag, iris, and subtropical bedding at the rear; fountain covered with parrot's feather _(Myriophyllum proserpinacoides_).]
Usually the ponds or tanks are not cement lined. In some soils a simple excavation will hold water, but it is usually necessary to give the tank some kind of lining. Clay is often used. The bottom and sides of the tank are pounded firm, and then covered with 3 to 6 in. of clay, which has been kneaded in the hands, or pounded and worked in a box. Handfuls or shovelfuls of the material are thrown forcibly upon the earth, the operator being careful not to walk upon the work. The clay is smoothed by means of a spade or maul, and it is then sanded.
The water for the lily pond may be derived from a brook, spring, well, or a city water supply. The plants will thrive in any water that is used for domestic purposes. It is important that the water does not become stagnant and a breeding place for mosquitoes. There should be an outlet in the nature of a stand-pipe, that will control the depth of water. It is not necessary that the water run through the pond or tank rapidly, but only that a slow change take place. Sometimes the water is allowed to enter through a fountain-vase, in which water plants (such as parrot's feather) may be grown (Plate X).
In all ponds, a foot or 15 in. is sufficient depth of water to stand above the crowns of the plants; and the greatest depth of water should not be more than 3 ft. for all kinds of water-lilies. Half this depth is often sufficient. The soil should be 1 to 2 ft. deep, and very rich. Old cow manure may be mixed with rich loam. For the nympheas or water-lilies, 9 to 12 in. of soil is sufficient. Most of the foreign water-lilies are not hardy, but some of them may be grown with ease if the pond is covered in winter.
Roots of hardy water-lilies may be planted as soon as the pond is clear of frost, but the tender kinds (which are also to be taken up in the fall) should not be planted till it is time to plant out geraniums. Sink the roots into the mud so that they are just buried, and weight them down with a stone or clod. The nelumbium, or so-called Egyptian lotus, should not be transplanted till growth begins to show in the roots in the spring. The roots are cleaned of decayed parts and covered with about 3 in. of soil. A foot or so of water is sufficient for lotus ponds. The roots of Egyptian lotus must not freeze. The roots of all water-lily-like plants should be frequently divided and renewed.
With hardy aquatics, the water and roots are allowed to remain naturally over winter. In very cold climates, the pond is protected by throwing boards over it and covering with hay, straw, or evergreen boughs. It is well to supply an additional depth of water as a further protection.
As a landscape feature, the pond should have a background, or setting, and its edges should be relieved, at least on sides and back, by plantings of bog plants. In permanent ponds of large size, plantings of willows, osiers, and other shrubbery may set off the area to advantage. Many of the wild marsh and pond plants are excellent for marginal plantings, as sedges, cat-tail, sweet-flag (there is a striped-leaved form), and some of the marsh grasses. Japanese iris makes an excellent effect in such places. For summer planting in or near ponds, caladium, umbrella-plant, and papyrus are good.
If there is a stream, "branch," or "run" through the place, it may often be made one of the most attractive parts of the premises by colonizing bog plants along it.