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After about 3 weeks, lower the pot so 8 to 10 inches (20 to 25 cm) of water covers the crown. As it grows, gradually lower it until 12 to 18 inches (30 to 46 cm) of water covers the crown. If you plant in spring, you should see flowers by June. Flowers last 3 to 4 days, and should be trimmed and removed when they whither. You should also remove old leaves to prevent rot. Deadheading, or removing old flowers and leaves, will help keep your water clear and encourage new flowers to form. Lilies are hungry plants, and should be fertilized with a slow release aquatic formula every 4 to 6 weeks. Lift the pot out of the water, and use your fingers to clear out small holes in the gravel and soil. Insert aquatic fertilizer tablets or pellets, then smooth over the gravel and submerge the pot. The amount of fertilizer to add depends on your product, so check its label for specific instructions. Some aquatic fertilizers specify 1 tablet per 1 gallon (3.8 L) of soil, while other products recommend 2 to 4 tablets for the same amount of soil. If your pond freezes solid, you’ll need to winterize hardy lilies inside, too. Store the pot in a large aquarium filled with water.  If you can't store the entire pot, trim the leaves and remove the rhizome, then apply a dusting of fungicide. Store the rhizome in a plastic bag filled with peat moss, and keep the bag in a cool, moist place, such as a basement. If your pond is at least 18 inches (46 cm) deep and doesn’t completely freeze, you can winterize your hardy lilies outside. Place the pot in the deepest part of the pond, where it'll be protected from cold air. Eventually, the rhizome will start to crowd the pot, and you’ll need to divide it. In the spring, remove the rhizome, or root ball, from the pot and rinse away excess soil from the roots. Look for tuber-like shoots with distinct growing tips or emerging stems. Using a knife or pruning shears, cut the shoots and surrounding roots in lengths of at least 3 inches (7.6 cm) from the rest of the root ball. You’ll likely be able to divide the root ball into several shoots. Plant each shoot in a separate container, then place them in your pond or give them to a friend.
Place the container at gradually deeper water levels. Remove old flowers and leaves before they rot. Fertilize lilies monthly during the growing season. Bring tropical lilies inside when the water temperature dips below 65 °F (18 °C). Divide an overgrown lily every 2 to 3 years.