I found great success with the Jobes fertilizer spikes. I fertilize monthly during the growing season. I put one spike at 12, one at 3, one at 6 and one at 9 as you would read a clock, with hands. They are inexpensive and can be found at almost all hardware stores. If you have had your lilies for a season, make sure to check the roots. Sometimes the plants get root bound. White roots will run around the inside of the pot and the plant growth will suffer. I live in Florida and have to trim the roots every 3 to 4 months. Might explain the excessive root growth. Also check the location of your plants. My plants sit in a dedicated pond without any moving water. Some lilies I have had refuse to flower when there is too much current. Good Luck!