The hardy water-lilies give no trouble in winter as they are simply left outdoors where they grew. They take care of themselves! Natural ponds must obviously remain undisturbed; artificial ponds can have some water drained off, and in places where the winter cold is likely to be very intense, the plants can be covered with planks, hay, leaves or any other protective material ready at hand. Where hardy nymphaeas have been grown in tubs plunged in the ground, a simple covering with hay is sufficient. Loose tubs can either be plunged in the ground or removed to a cool cellar. When spring returns, the covering is removed at the same time as it is taken off other garden plants; the tubs can be brought from the cellar in March.
On the other hand, wintering the tender, day blooming water-lilies is really a difficult matter, requiring some skill and a good deal of space. Full-grown plants may be taken up bodily before frost, either in their tubs, or with a big ball of earth, and wintered in a large, warm tank indoors-there they will keep on blooming, with plenty of heat and light; or will merely keep alive in lower temperatures. Plants which have grown large and flowered, will not live over in any other way, excepting Nymphaea flavo-virens and its kin. Usually, therefore, the old plants are left outside to die; but the tubers may be collected.
The night bloomers are wintered more easily than the tender day bloomers. The plants may be taken from the pond either in their tubs, or with a large ball of earth, in October, and allowed to dry off slowly. In a month’s time there should remain from each plant one or two small tubers. Sometimes the tuber is smooth and oval; sometimes it is of a very irregular shape. It is kept in dry sand as prescribed for the day blooming kinds. In February or March the tuber is planted in sand and sunk in a warm tank. Soon it sends out a host of shoots. These mature one by one. They may be broken off and potted separately as soon as they have one or two floating leaves. Each tuber, therefore, of the night blooming waterlilies will produce enough plants to stock a large pond. It is a wise precaution to keep one or two plants in small pots all summer, just to form tubers. The old plants sometimes rot completely when taken in.
Tender nymphaeas that are to be carried over the winter for another season must be taken up before there is a chance of a killing frost, that is between October 15th and 30th. If possible, drain the pond of enough water to facilitate the work, removing the leaves from the plants and cutting off the roots about a foot from the center. Then take up the plants with as much soil as will cling to them.
The best winter quarters for the tender nymphaeas is under the bench of a greenhouse with a temperature of from 60° to 65° F.
With the mud clinging to them they show no differences. But most of the stellata type, such as Nymphtaea cterulea, have a central crown only, while others have one large and a varying number of smaller tubers. These mature during the next month or so, finally going into a dormant condition. Many of the stellata type produce tubers very sparingly and it is often necessary to retain the old rhizome. This old rhizome, however, has a tendency to rot during the winter when placed under the greenhouse bench, to prevent which it must be kept in a growing condition. This is best accomplished by potting it into a 7-inch pot, which is then submerged in a tank in the greenhouse, only a slight covering of water being essential. By the next spring the plant will be found ready to make a vigorous growth.
IN JANUARY
About the middle of January look over the collection to see what can be saved and what must be thrown away. In this the greatest care must be exercised as many of the most valuable types produce tubers often not larger than a pea.
While sorting the tubers, carefully remove the mud clinging to them, taking care not to injure the eyes. Then place them in rather dry sand, where they can remain till the time comes to start them into growth.