Each year we get a few frantic eMails from customers, mostly those along the northern tier of states.
The first matter of concern is pond temperature. Your pond must have reached 70F degrees before placing Tropical Lilys. This is because Tropicals will fall back into dormancy if placed into cooler water. When that happens, they loose all of their pads and look dead. Actually, the tuber is sleeping. Depending upon the temperature, it may or may not wake up again.
Next is planting. Most Tropicals get BIG, except for the miniatures. Use three gallon pots, or better yet, use the widest container you can find as a pot. Here, we place 2" of cement mortar at the bottom of all pots. This keeps them from tipping when the large Koi decide to start digging for worms. The Lily needs 6-8 inches of soil. The roots will fan out. Place 10-15 grams of pond tab fertilizer at the bottom before adding soil. Place the plant so the crown will be at the dirt line. Cover the dirt with thin flat rocks leaving space for new leaves. This will discourage critters from digging. Then place the pot in a large container of water and let the debris rise where it can be skimmed off. This keeps the mess out of your pond. Place the pot at a height where the pads are near the surface, the new pads will adjust to the water level. Then lower it a little each week untill the crown is 12-18 inches below the surface.
Fertilizer is critical, but any slow release pond tab will work fine. They are available in 5 and 10 gram sizes. We use one of the 10 gram sized tabs under each new Lily and push another down deep into the roots monthly during the growing season. You could mix granulated fertilizer in the bottom couple inches of dirt if you don't have tabs, but be careful not to let roots get too close or they could burn. Granulated fertilizer is impossible to use later in the season without getting it into your water where it will cause an algae bloom. Pond fertilizer tabs are inexpensive and you should always keep a few on hand. We normally include one 10 gram tab with each new lily purchase.
Propagation is the last important part of growing Tropical Lilys. Your Tropicals will die at the end of the season. Tropicals propagate from the golfball sized tubers that will grow along their roots. In the fall, and before the water gets below 60F, you must harvest the tubers. Dump the pot out and dig thru the dirt for them. Then wash them clean and place them in slightly damp Peat Moss. Keep the tubers above 50F in a cool dark place. In the following spring, you can plant the tubers. For a great headstart on the next season, try this. About a month before your water will reach 70F, place the tubers in an aquarium or other well lighted container above 70F and they will sprout. If you wait untill the sprout develops three or more true leaves and a few roots, it can be pinched off to form a separate plant. Often, you can get as many as 20 plants from one tuber. Then the problem becomes keeping fish, crayfish, turtles and others away from your new Lilys. They consider these fine growths as salad and will continue to chew them off until the tuber dies.