There is no denying the beauty of water lilies, and no garden pool is truly complete without at least one lily gracing its placid waters. Still, there are so many varieties to choose from, selecting the species just right for your conditions can be a mystery. Where do you start? It is actually very simple: Take a few minutes to observe some basic conditions in and around your pool, then sit back with some garden catalogs and pick out your favorite color.
Research your climate zone using a hardiness map available through the U.S. Department of Agriculture online (see Resources). Use the map to find the first and last frost dates for your area.
Determine the minimum depth of the pool where you will plant your lily. Hardy lilies require 6 to 30 inches of water above their soil level to remain frost-tolerant, so deeper pools offer a wider choice of winter hardy species. Tropicals are only hardy in zones 10 and 11, remaining frost-tender above those zones. Plan to bring in or protect tropical lilies in all but zones 10 and 11 during winter; and hardy lilies if you live above zone 3.
Monitor the amount of sun your pool gets throughout the day. Choose lilies that thrive in sunlight conditions matching yours. Most hardy lilies require a minimum of five to six hours per day, while tropical lilies will get by with four.
Take your pond's temperature with a pool thermometer. Hardy lilies will survive cool water, but tropical lilies need water above 70 degrees Fahrenheit year round to thrive.
Consider the size of your pool or pond. Lilies require space, though some are more compact growers than others. A rule of thumb is 4 square feet per plant on average. But be aware that there are species, like those in the tropical South American genus Victoria, that may require as much as 6 square feet for each leaf. Check specific growing information before planting.
Browse catalogs and nurseries for lilies meeting the criteria/conditions surveyed in these steps.