How to grow agapanthus
These dramatic sun-loving border plants produce large spherical flowerheads, usually in beautiful shades of blue, from midsummer onwards. These sway on tall stems above clumps of strappy foliage. Some types, especially the evergreens, may not be fully hardy, so are best grown in containers that can be protected from frost over winter
- Showy flowers in shades of blue, purple and sometimes white
- Agapanthus flower for a long period, mid-summer to early autumn
- A good border plant
- Suitable for containers
- Thrives in sun
- Plant in spring, from the end of March into April
- Some agapanthus are evergreen
All you need to know
Choosing an agapanthus
There’s a lot of variety in agapanthus so, when selecting the right one for you, it helps to bear in mind the following things:
- Agapanthus range in height, some are quite small 20-60cm (8in-2ft); while others can grow up to 1.5 m (5ft). Use the shorter ones at the front of the border, taller ones to the middle of the border. All sizes can be grown in containers
- Flower colour is key. There are inky blues, pale sapphires, purples and whites. Choose a shade that you like and works with the plants you plan to put it next to
- Deciduous types which lose their leaves are the toughest, hardest agapanthus. However, some agapanthus are tender (mainly the evergreen types) and these are best overwintered in a cool greenhouse
- Flowers are mainly rounded with trumpet shape. The more unusual agapanthus have pendent blooms in rounded flower heads
- Go for agapanthus that have received the RHS Award of Garden Merit as these have been tested and perform well in average garden conditions
- Buy hardy types in spring ideally. You can buy tender evergreen types at this time too, but they will need protection from frost
- You can buy potted plants in flower in summer, but be prepared to keep them well watered for the rest of the summer so they establish well
- Buy in containers and not in a packet, as the plant may have dried out and will be less likely to thrive
Grow all agapanthus in well-drained soil in full sun. Avoid planting in shade as they won't flower much.
In the border, ideally plant your agapanthus in spring. If they are growing in containers, plant them the same depth that they are in the pot. If you have bought bulbs or fleshy rhizomes, the noses should be covered with 5cm (2in) of soil.
If your soil is prone to waterlogging, or you live in a cold area, grow agapanthus in containers.
Grow single plants in 20-23cm (8-9in) in diameter containers using a loam-based compost, such as John Innes No. 2 or No. 3. All container plants (hardy or tender) benefit from some winter protection (see Overwintering below).
- Water regularly in the growing season, especially in the first year after planting. Once established they will need little watering, but some in late summer in very dry years will help ensure good flowering in the next year.
- Feed border plants in spring when they start to come into growth with a balanced fertiliser, such as Vitax Q4, Growmore or fish, blood and bone at the manufacturers recommended dose
- For containers, use a liquid fertiliser, such as Phostrogen or seaweed feed, diluting according to the instructions on the bottle. Feed fortnightly from April until flowers begin to show colour
Deadheading and cutting back
- Dead head when flowers have faded, cutting them off at their base. This will encourage plant to flower longer, but some people also like to leave on the seedheads for early winter interest
- Remove the flowered stems and yellowed leaves of deciduous types in the autumn, as they natural die back. Tatty leaves on evergreens can be taken off at any time
- Protect your potted plants in autumn by placing in a light, frost-free place, ideally sheltered from the worst of the winter rains. This might be a cool greenhouse or coldframe, but place at the bottom of a south- or west-facing wall if you don't have one. Wrap all agapanthus (hardy and tender types) in two to three layers of horticultural fleece for protection from November to early April
- Evergreen plants and the more tender varieties do need winter protection. A few layers of horticultural fleece can also be thrown over the leaves of the evergreen varieties. Alternatively, in colder areas the more tender evergreen types can be grown in containers and moved to a frost-free greenhouse or conservatory for the winter
- If you live in a cold area, you can help plants to survive the winter in borders by applying a 15-23cm (6-9in) deep layer of mulch around plants in autumn or early winter and remove in spring before growth starts. For the mulch, you can use sand, home-made compost, chipped bark or straw
Established clumps can be lifted and divided into smaller clumps. Spring (late March and April) is the best time to do it. This is the best way to make more plants of a cultivar as all the new clumps will be exactly the same.
Agapanthus can also be propagated from seed, however the resulting plants will be different from their parents. In fact each one will be unique, so you might get a gem among the seedlings.
Despite being easy to grow, agapanthus are occasionally subject to problems.
Agapanthus gall midge
Preventing winter damage
It is naturally disappointing when agapanthus don't flower well. It's quite a common problem, however, and thankfully one that can be resolved.
To ensure a good display next year, keep plants well-watered through summer until early autumn, which will encourage the development of new flower buds.
Although often said, agapanthus don't actually flower better when pot-bound. It's true they like to be cosy in their pot, flowering poorly when overpotted or over-divided, but they are also shy to flower when excessively pot-bound. So do try potting up into a container 2.5 - 5cm (1-2in) larger all round every two or three years, plus watering and feeding from spring to early autumn to improve flowering. Once potting up in a larger container is no longer practical, consider dividing in spring.
Too much shade, cold weather and lack of winter protection are also common reasons for agapanthus to fail to flower.
Too much winter warmth may lead to early flowering, but the flower quality will be poor.
If you are a member of the RHS, you can use our online Gardening Advice service.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.