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By Karen Stewart
Water lilies are classified as either hardy or tropical. Hardies will survive Iowa winters if below ice level. Tropicals will not survive Iowa winters; treat as annuals or try saving the tubers. Check water garden books, catalogs, and your local dealers for recommended varieties.
Planting depths (water depth over the crown) vary with plant size and variety Check sources which give plant descriptions, planting depths and recommended container sizes. Container size should be at least 10" x 7" unless plants are mini- or dwarf. I prefer the heavy-duty, black plastic aquatic containers (no holes). Avoid copper and redwood, which are toxic to plants and fish!! Remember: You have to move the pots!
Hardies may be overwintered below ice level in the pond; tropicals should not be planted until water temps are consistently above 70 degrees!! Most hardy rhizomes grow horizontally; plant at a 30-45 degree angle with the cut rhizome end at the container's side and growing tip facing the center. Plant tropical tubers and hardies with upright rhizomes in the center of the container. Do not cover the growing tip with soil or gravel! When dividing an existing lily or planting a new rhizome, remove most long, brown anchor roots and spongy, old rhizome material; the new rhizome section should be 3-6" long, with newer, white nutrient roots attached.
Planting mediums include: heavy garden soil, regular (non-scooping) unscented cat litter, "clay soil conditioner", manufactured non-soil aquatic mediums. Top dressings include: pea gravel, "pond pebbles", river rock, lava rock. If fish are present (especially koi), use rocks larger than pea gravel. Experiment for bet results I your particular situation. Fertilize as recommended for plant and container size using aquatic fertilizer tablets pushed deeply into the soil near the roots.
Lower the plant slowly into the water so that air escaping from the planting medium will not disturb the top dressing. Shallow depth placement for the particular variety will encourage new growth; pot may be lowered to recommended depth as lily established itself. Use plastic storage (milk) crates or bricks to elevate the planting container. If unsure of the correct depth, err on the shallow side. Feed lilies 1-2 times per month during the growing season; amount and timing depends upon plant size, variety and fertilizer instructions. Cease feeding approximately one month before killing frost is expected.
Remove spent blossoms and decaying/damaged leaves by pinching off stems near the plant's crown; this grooms the plant, encourages new growth, and helps prevent insect infestations. Inspect plants regularly and remove debris or insects. After killing frost, remove foliage and lower plant below ice level (if hardy).