How to Plant, Grow, and Care for Agapanthus

A beautiful perennial with an attractive leaf structure and season-long interest, agapanthus is one of those plants that can really test a gardener’s identification skills. Happen upon some on a stroll through your neighbor’s yard or a visit to your local botanical garden, and it may take you a beat to accurately come up with the genus. 

What is Agapanthus?

With long, strappy leaves, agapanthus resembles an iris (or a daylily or an ornamental grass). The flowers have a dome or globe shape like an allium (or a globe thistle or a milkweed). Its nickname (lily of the Nile) makes things even more confusing since agapanthus flowers resemble a miniature version of the traditional lily.

In fact, the genus is so close to so many others botanically that it’s been assigned and reassigned to several different plant groups before recently earning its own family, agapanthaceae.

Once you get to know this lovely plant, however, we’re sure you’ll never misidentify it again (and that you’re going to want to grow some in your own backyard). Read on for a detailed exploration of the agapanthus genus, including its characteristics, history, growing preferences, maintenance requirements, and problem areas. 

Characteristics

Hardy in zones 8-10, agapanthus is a tender, herbaceous perennial with a round arching habit. Its strappy leaves are dark green and glossy with a prominent midrib crease and a length averaging somewhere between one and two feet. Some have variegated leaves with white centers or margins. Many are evergreen and will hold their color throughout winter.

Agapanthus roots are tuberous and plants grow from the center outward as the rhizomes spread. Inflorescences are terminal and emerge as green bulb-shaped buds on thick, upright stems that float above the foliage. Flowering occurs at least once in summer and often repeats in regions with longer seasons. 

Blooms have a rounded umbel shape and contain 20 to 100 small, bell-shaped flowers. Each has six reflexive petals and a deep throat with a central stamen cluster. Coloring can be white to dark purple, and petal midribs are usually darker than their margins. 

History & Cultivation

The genus has a confusing taxonomic history. Once a monotypic family consisting of only one genus, Amaryllidaceae includes multiple species, and hundreds of cultivars. 

Despite its misleading nickname (Lily of the Nile), the Agapanthus genus is native to southern Africa rather than northeast Africa’s Nile River basin. Brought to Europe by African explorers in the late 1600s. The plant has medicinal purposes. Its parts were used to treat paralysis, heart disease, respiratory conditions, and a variety of other ailments, and its leaves were used as bandages.

Planting

You can plant agapanthus in a container, ideally in spring or fall. Hardy in zones 8-10, you can grow it in the ground year-round in warmer parts of the globe. In zones below 8, plant them when soil temperatures exceed 50 degrees Fahrenheit (10 degrees Celsius) and bring them in for winter. 

In the Ground

Plant agapanthus 12 to 18 inches apart. Dig a shallow trench that’s roughly two inches deep and set rhizomes in the soil with their eyes or green shoots directed upward. Cover loosely with soil so that the top quarter of the rhizomes are slightly exposed.

In a Container

Select a well-draining pot that’s 10 to 12 inches wide to accommodate agapanthus’ mature width. Agapanthus blooms more prolifically with constricted roots, so anything larger than 12 inches might lead to a more foliage-heavy specimen. Fill your container with a fertile potting mix. Set rhizomes in a shallow trench that’s two inches deep and cover loosely with potting mix. 

Established Plants

If you’ve purchased a flowering agapanthus plant from a garden center or received one from a fellow gardener, dig a hole that’s just as deep and roughly twice as wide as the plant’s root mass. Set the root mass in your hole so that the plant’s crown sits just above the soil surface, and backfill with soil (or potting mix, if you’re planting in a container). 

How to Grow

Agapanthus plants are easy to grow and care for as long as you know what kind of species you have and your hardiness zone. Leave deciduous varieties in the ground where they are hardy or overwinter them in a cool, dark place in regions with cold winters. 

Evergreen varieties are particularly cold-sensitive. Bring them inside if temperatures are expected to dip below 50 degrees F (10 degrees C). Note that evergreen species will not go dormant like deciduous species but will cycle through their bloom periods like a houseplant, requiring sun and water year-round. 

When given a generous amount of natural light, rich soil, and good drainage, agapanthus plants can live for up to 10 years. Here’s a look at this unique plant’s specific growing requirements:

Light

Agapanthus plants require full sun to flower fully and achieve firm, green, healthy foliage. Site them where they will receive at least six hours of direct, unfiltered light.

In regions with hot afternoon temperatures and scorching sun, choose a location that offers six hours in the cooler parts of the day. An east-facing bed with some afternoon shade is ideal. 

Water

Water new plants about one inch per week while they are setting roots and adapting to a new location. Once established, reduce watering to about one-half inch per week. Use a rain gauge or monitor your local precipitation levels to make sure you’re providing enough but not too much water.

Direct supplemental irrigation at your plant’s roots and not its leaves or flowers. Use a soaker hose or a low, slow setting on your hose nozzle, and water in the morning if possible. This will give condensation on leaf surfaces a chance to evaporate throughout the day and discourage fungal conditions. 

Soil

Agapanthus is tolerant of a wide variety of soil conditions but grows best in light, loamy soil that drains quickly. Evergreen species enjoy a little sand worked into the mix.

Container-grown agapanthus plants enjoy a light potting mix that’s slightly acidic. For both potted and in-ground plants, shoot for a pH level that’s somewhere between 5.5 and 6.5 for best results. 

Maintenance

Once its growing needs are met, caring for agapanthus is not difficult, and its maintenance will not demand too much of your time and attention. Gardeners in zones that occasionally but do not regularly freeze will likely have to think about this plant more than others, and gardeners below this plant’s zone 8 cutoff will have to think about overwintering. Outside of these concerns, maintaining agapanthus is fairly straightforward.

Mulch

A two to three-inch layer of organic mulch will protect agapanthus from cold winter temperatures while keeping its roots moist and discouraging puddles. It will also nourish the soil and decompose over time.

Hardwood chips, composted yard waste, leaf litter, and straw are all good choices for mulching agapanthus. Pull mulch away from plant crowns in spring when the sun begins to warm the soil.

Fertilizing

This plant will benefit from a fertilizer application in early spring and again two months later when flowering is about to begin. Choose a balanced granular fertilizer with an even NPK ratio (10-10-10) or one with a slightly higher phosphorus content (5-10-10) if you want to encourage flowers over foliage. Apply as directed and water immediately.

Deadheading

Depending on where you live, agapanthus will flower at least once in early summer for a period of about three weeks. In warmer regions, a second wave can be expected later in summer, especially if spent blooms are deadheaded promptly. 

Removing faded flowers will tell roots that seeds have not been spread and reproduction has failed. This will signal them to send up more blooms in an effort to create more seeds and, thus, result in more flowers. Deadhead spent agapanthus flowers by cutting their stems down to the base with a clean, sharp pruning tool. 

Pruning/Cutback

Agapanthus does not need pruning throughout the season. If brown or yellow leaves appear, they can be snipped off to discourage disease, but healthy, green foliage must be left in place until the end of the season. Evergreen agapanthus should not be cut back at all unless there is a health problem. 

When the leaves of a deciduous agapanthus plant turn brown in fall, this is a signal that they are entering dormancy and are ready to be cut back. Using clean, sharp bypass pruners or loppers, cut leaves down to about three inches above the plant’s crown. This will tell the roots to nourish next year’s plants rather than this one’s. 

Overwintering

Plants that are hardy can be left in the ground after being cut back as long as temperatures are expected to remain above 50 degrees (10°C). Those grown in pots and those grown in regions where the genus is not hardy (below zone 8) can be stored in a cool, dark room or garage that doesn’t freeze. Rhizomes can also be dug up, cleaned off, and wrapped in paper if storage space is limited.  

Division

Although agapanthus plants flower prolifically when roots are densely packed, they do require division every three years or so to keep their upright habit. To perform this basic maintenance task, follow these steps:

1. Carefully lift the entire plant from the ground or its container. 
2. Lay it flat on a tarp or hard surface and brush off the dirt so rhizomes are somewhat exposed.
3. Use a knife or flat garden shovel to slice the root mass into equal sections or break off individual rhizomes with your hands.
4. In each new section, be sure to include some rhizomes (the fleshy potato part), some fibrous root hairs, and some eyes (green shoots or brown bumps). 
5. Replant as you would a new agapanthus plant.  

Propagation

Although seeds can be collected from faded flowers and planted directly in the soil, this is not the recommended method for propagating agapanthus plants. Not only do seeds take several years to establish, but new plants will not likely resemble the original since most nursery-sold agapanthus plants are hybrids. 

Division is by far the most effective method for turning one agapanthus plant into several, and since the process is asexual, the new plant will be an exact clone of its parent.  

Varieties

It’s unlikely you will purchase an agapanthus plant in your local garden center that hails from a true, singular species. These exist in the wilds of southern Africa but not anywhere else in the world. The genus crosses easily with itself, and the ornamental cultivars are usually derived from blended species. 

For this reason, most plant tags will not reference a specific agapanthus species at all and will just cite the genus and cultivar. You will also frequently see plants in this group generically referred to as an ‘African lily.’ 

Be sure to check hardiness zones and plant descriptions to determine if you’re getting a deciduous or evergreen variety. Here’s a look at some of the most common agapanthus cultivars and a brief description of each.

Brilliant Blue

This deciduous variety has loose umbels of violet-blue, trumpet-shaped flowers with dark midribs. At maturity, each plant produces roughly 100 flowers per summer. Considered a dwarf, ‘Brilliant Blue’ maxes out at 18 inches. It’s considered semi-evergreen and hardy in zones 8-11. 

Polar Ice

Blooming prolifically from mid-summer to early fall, this bright and cheerful agapanthus cultivar features snow-white flower clusters and grows up to three feet tall. The leaves are upright and bright green, arching slightly at their peaks. This one tolerates a bit more chill and can survive without fuss in zones 8-11. 

Fireworks

This compact, evergreen cultivar earns its name for resembling a festive burst of sparks in the night sky. The flowers are two-toned and trumpet-shaped, with lavender throats that transition to white at the petal tips. Maxing out at two feet tall, ‘Fireworks’ remains green year round and is hardy in zones 8-11. 

Common Problems

When properly planted and maintained, agapanthus plants are known for being highly resistant to pests and diseases. There are a few to watch out for, however. Here’s a quick look:

Diseases

The diseases that most affect agapanthus are all fungal in nature, and root rot tops the list. Brought on by poor drainage, overzealous watering practices, and/or excessive precipitation, root rot is a fungal condition that kills a plant from the ground up. Characterized by wilted or yellowing leaves, mushy rhizomes, and a foul smell, root rot is almost always fatal, and agapanthus plants afflicted with this disease should be destroyed.

Gray mold is also brought on by excessive moisture or improper drainage. Symptoms of this fungus include a fuzzy, gray covering on leaves and stems. You might also notice a ring in the soil around your plant’s crown. If you suspect gray mold, snip away the affected plant parts promptly, and it has a good chance of recovering fully. 

Powdery mildew is a mostly aesthetic fungal condition brought on by excess moisture and inadequate airflow. Symptoms include a dark gray or black coating on leaves, stems, and possibly flowers. Look for it after cool, wet periods and remove affected tissue from the garden. Powdery mildew is not life-threatening, but it can overwinter in the soil, so keep things tidy to prevent an ongoing problem. 

Insects & Critters

If you’re noticing cotton-like masses on your agapanthus plant’s leaves or stems, you may have a mealybug infestation. These sap-sucking insects drain the nutrients from plant tissue and leave a sticky excrement behind that attracts ants. 

Spider mites will produce a white, stringy webbing that’s slightly less dense than mealybugs, and you may notice white puncture marks on leaf tissue. They will also leave a sooty residue that attracts other insects and diseases. 

Look for chewed leaf margins and slimy trails on their undersides to indicate a problem with snails or slugs. Since they are most active at night, particularly during cool, wet periods, the best way to confirm their presence is with a flashlight after dark. 

The solution for dealing with insects that attack your agapanthus plants is generally the same for all. A regular, hard blast from the hose and/or manual removal are going to be your best weapons. Slugs and snails can be deterred with beer traps or bait you can purchase at your local hardware store.

Frequently Asked Questions