The peace lily isn't a "true" lily, because it doesn't belong to the Lilium genus. Although the peace lily usually is considered an indoor plant, it can thrive when planted outdoors as long as it isn't placed in direct sunlight. You'll need to grow your outdoor peace lily in a pot, though, so you can easily move it indoors for cold fall and winter weather. Peace lilies are injured by temperatures below 15.6 degrees C, but they are hardy in U.S. Department of Agriculture zones 10 and 11.
Find a place in your yard that gets a lot of indirect light and is sheltered from wind. Choose a covered spot if your area gets a lot of rain.
Fill your watering can the day before you plan to plant your peace lily. Leave the can outside, next to where you'll place your plant. This allows the chlorine in the water plenty of time to evaporate and the water will be the same temperature as the plant.
Remove your indoor peace lily from its container and soil. Split the plant in two by carefully pulling its roots apart, working from the top to the bottom. Examine the untangled roots to determine where an offshoot begins. Cut the offshoot carefully away at the roots, leaving intact as much of the top of the roots as possible.
Partially fill your 6-inch-diameter pot with potting soil. Put half of the peace lily into the pot, at roughly the same depth as the parent plant was planted. Cover the root ball with potting soil. Add extra soil if the plant is leaning. Do not fertilise.
Water your peace lily as often as necessary to keep its soil moist, but not saturated. Allow the soil to dry up somewhat -- but never completely -- between waterings. Fill the pot's saucer with water first and allow some of the water to absorb into the plant's roots. Then water the plant's foliage and the top of the soil.
Fertilise after your outdoor peace lily is well-established. Add liquid fertiliser to a bucket, then add an equal amount of water to dilute it; peace lilies react poorly to being fertilised too much. Only fertilise three or four times a year.
Bring the plant indoors if the weather gets too wet or cold. Repot your peace lily at least every three years to refresh its soil and avoid growth problems.
Skip watering if there has been recent rainfall. If your peace lily's leaf tips turn brown after fertilising, the mixture may have been too strong. While you could grow your peace lily from a seed, it would take several years to bloom. Propagating using crown offshoots is a much more effective and immediately rewarding method.