Getting closer to the time of year where people start wondering "now how am I going to do this?."
Quoting:
Horticulture, The Art of American Gardening, Sept 1999 v96 i7 p30
Overwintering a Tropical Water Lily. (Brief Article) JANET H. SANCHEZ.
Full Text: COPYRIGHT 1999 PRIMEDIA Special Interest Publications
THE ROMANTIC, COLORFUL BLOSSOMS of tropical water lilies (Nymphaea spp.) add drama and fragrance to ponds in summer and early fall. Unlike hardy water lilies, tropicals are available in stunning shades of blue, violet, and purple, and many open their exquisite blooms in the evening. Yet since many of these plants are descended from water lilies native to South America, Mexico, Africa, and Asia, they will perish over the winter in all but the warmer parts of USDA Zones 9 and 10. While some gardeners treat them as annuals (and costly annuals at that), a little effort will allow you to overwinter them indoors by saving the dormant tubers.
To encourage the onset of dormancy, stop fertilizing your tropical water lilies six weeks before the first expected frost.
1. Retrieve the Tubers
As air and water temperatures cool, the leaves will turn yellow and die. After the first few frosts, or when the water temperature in your pond has dropped to 50[degrees]F, remove the plant from the pond. Tip the water lily out of its pot and hose off most of the soil. Check among and beneath the roots for the tubers, which will be hard and dark brown, and about the size of hickory nuts or walnuts. Snap them off with your fingers and put them in a shady, warm place to air dry for a few days. Remove any remaining pieces of root or stem.
2. Pack the Tubers in Sand
Fill a pail with clean builder's sand and moisten it with water. The idea is to just dampen the sand, rather than make it dripping wet. Fill a resealable plastic bag halfway with sand. Set the tuber on top of the sand and cover it completely with more sand. If you have multiple tubers, give each its own bag. Add plastic labels, marked with indelible ink, before sealing the bags (for future identification).
Store the bags in a cool, dark place, where the temperature ranges from 50[degrees] to 55[degrees]F. Do not let them freeze. Over the course of the winter, check the bags to make sure the sand remains damp.
3. Repot and Submerge the Tubers
Six weeks before your last expected frost, pot up each tuber in its own small, two-or three-inch pot of good topsoil, setting each about an inch deep. A thin layer of gravel over the top will help to keep the soil in place when the pot is submerged. Then set the pots in a large pail of water or in an aquarium. There should be three inches of water over the rim of the pots. Place the pail or aquarium in a sunny spot or under supplemental lighting. A water temperature of 70[degrees]F should stimulate growth; colder water will shock the plant and delay growth. You may need to use an aquarium heater to warm the water.
4. Pot up the Plantlets
After a few weeks, each tuber will produce one or more plantlets. When their leaves are large enough to float on the surface of the water, pot them up into four- or five-inch pots of clayey soil. (If you get more than one shoot, you can divide them and pot them individually.) Put the pots back in the pail or aquarium quickly so that the plants don't dry out.
5. Repot and Transfer to the Pond
When your pond has reached 70[degrees]F, repot each plant in a large container, such as a 19-quart water-lily pan, of heavy garden soil. Center the crown and keep it slightly above soil level. Tropical water lilies are heavy feeders; add a couple of fertilizer tablets specially formulated for water lilies. Finish with a layer of gravel or pebbles. Set the pan back in the pond with its rim 8 to 12 inches below the surface of the water. As the leaves grow and reach the surface, lower the tub to 18 inches.
OTHER METHODS Some tropical water lilies, such as `Dauben' (which is among the easiest to grow), are viviparous, producing tiny plantlets at the sinus, or center meeting point of a leaf's lobes. Once rooted, these plantlets can be potted up and overwintered in an aquarium. If you have the room, an alternative method practiced by many gardeners (and favored by the late Henry Mitchell) is to lift and save the entire plant after the first few frosts. Keep as much of the soil around the roots as possible and put the plant in a large waterproof tub. Trim off the old leaves and place the tub in a sunny southern window or in a greenhouse, covering the roots with six inches of water. Growth may not occur during the winter, but will pick up again in the spring. When your pond is warm enough, repot the water lily in fresh soil, fertilize it, and return it outdoors.--J.H.S.
