With strappy leaves and umbels of summer-blooming flowers in shades of blue, purple or white, lily of the Nile (Agapanthus spp.) plants grow from rhizomes to reach heights between 6 inches and 5 feet. Their hardiness varies from U.S. Department of Agriculture plant hardiness zones 7 through 11. To bloom, all varieties require plenty of sun, food and water, as well as somewhat crowded conditions and a winter rest.
Give It Sun
A lily of the Nile plant should receive at least three to four hours of sunlight – preferably more – per day. If you wish to grow it in a very hot climate, position the plant where it receives its sun during the morning, with shade during the afternoon.
Keep It Crowded
Lily of the Nile prefers to be a bit pot bound in a container, or somewhat crowded in the ground. After initially setting plants in the sandy loam of a garden bed, about 1 foot apart for smaller varieties and 1 1/2 feet apart for larger ones, you shouldn't need to disturb deciduous types until about six years later.
Evergreen varieties or those grown in large containers usually will need division or re-potting after four years or when the roots become so congested that they begin lifting the plants up out of their pots or out of the ground. Keep in mind that deciduous types often decline to bloom the year after being separated, while evergreen varieties flower most fervently just after being divided.
Feed It Well
In early spring, begin fertilizing an agapanthus plant once every two weeks with a balanced plant food, such as 20-20-20. Use 1 teaspoon of the crystals per gallon for an indoor plant and 1 tablespoon per gallon for an outdoor one. Once you move your indoor plant outside, after all danger of frost is past, raise the amount of plant food it receives to the outdoor rate. Continue this feeding program until the plant begins to bloom – usually in mid-summer -- after which you should fertilize it only once per month until it finishes flowering, typically in early autumn.
Care for In-Ground Plants
An in-ground lily of the Nile should receive about 1 inch of water per week during its growing season from early spring through early autumn.
- In USDA zones where it is hardy, a deciduous
type will die back to the ground over winter, at which point it should be
allowed to dry out somewhat. Don't remove its leaves until after they have yellowed and shriveled, as their death provides energy to the rhizomes for the following year.
- An evergreen variety should remain green during winter.
You can cover or surround either type with about 6 inches of straw and allow it to rest until spring.
Care for Container Plants
If you are growing lily of the Nile in a pot, water it frequently enough to keep its soil lightly damp over summer. Decrease that watering somewhat during autumn, and leave the plant outdoors until just before the first frost. At that point:
- Allow the soil of a deciduous type to dry out completely, and place the pot in a cool, unlighted location until early spring. You then can move it to a sunny windowsill and begin watering and feeding the rhizomes again.
- If your container lily of the Nile is an evergreen variety, bring it indoors for the winter to a chilly, bright position -- such as a sun porch or mud room -- with temperatures in the 40s or 50s Fahrenheit. Water it only about once a month until early spring, after which it can be watered and fed at the regular rate again.