Problems With Agapanthus

Plants in the Agapanthus genus, commonly called lily of the Nile, do not have major problems with disease or insects. The problems they have vary by species. Some require protection from cold weather, while others need extra water or require shallow, sandy soil to thrive. Evergreen and deciduous species generally grow in U.S. Department of Agriculture plant hardiness zones 8 through 11, although some cultivars will grow in colder climates.

Some agapanthus need protection from cold in climates that experience freezing weather. Cultivars of the deciduous bell agapanthus (Agapanthus campanulatu) will grow in USDA zones 8 through 10 and if they’re planted outdoors, they can survive temperatures that drop to 23 degrees Fahrenheit. If you mulch them with a 3-inch-layer of straw or leaves, they can survive to 20 F. Apply mulch when the weather cools in autumn but before the ground freezes and deciduous species have lost their leaves. Mulching them when the ground is warm and soft can provide a refuge for mice and other rodents. Evergreen species grow better where there's no hard freezes in winter. If you grow lilies in pots in USDA zone 8 or below, bring them indoors before the first fall frost. If you live in a cooler climate, the hybrid "Headbourne" agapanthus (Agapanthus "Headbourne") will grow in USDA zones 6 through 10.

Some agapanthus need regular and thorough watering to prevent problems. Evergreen blue lily (Agapanthus praecox) cultivars, the type you're likely to find at the garden center, will grow in USDA zones 8 through 11. They are sometimes mistakenly sold as African lily (Agapanthus africanus), which also grows in USDA zones 8 through 11. Because blue lilies come from rainy areas of South Africa, you may have to drench them thoroughly once a week and make sure they get plenty of water in spring and summer. To encourage them to form buds, keep the soil moist until after the flowers begin to fade in fall.

Agapanthus may stop flowering if they become too crowded over time. To ensure good flowering, dig up and divide evergreen plants every four years. Lift and divide the bulbs of deciduous species every six years. To divide agapanthus bulbs, simply ease the plant out of the ground or its container and use a sharp knife to divide the plant into healthy, roughly equal sections, each with roots attached. Plant the newly divided sections into fresh potting soil. You’ll have more success growing agapanthus if you pick a cultivar that matches the rainfall in your area. Bell agapanthus cultivars evolved in areas of South Africa with sparse rain in winter. Blue lily, African lily and other evergreen species evolved in areas with year-round rainfall.

Two agapanthus need a special setup in the garden if they're to live or thrive. African lilly subspecies (Agapanthus africanus subsp. africanus and Agapanthus africanus subsp. walshii) are both commonly called African lilies and also will grow in USDA zones 8 through 11. These subspecies are difficult to grow in gardens other than rockeries with plenty of rocks but little soil. Both are native to arid regions of South Africa with sandy, shallow soil and grow best in conditions that mimic their natural environment. That means shallow containers containing a slightly acidic, sandy mix. They do best when they’re pot bound. The subspecies walshii will only survive if grown in pots. To grow it successfully, you need a pot with plenty of drain holes and an extremely well-draining potting mix. Wet soil leaves these plants susceptible to root rot.