How to grow agapanthus

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
  

  Deciduous refers to plants (mainly trees and shrubs) that lose their leaves seasonally, usually during autumn. This is a natural process triggered by the season's shorter days and lower temperatures and allows plants to conserve energy during the winter months.

  types which lose their leaves are the toughest, hardiest 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

RHS hardiness ratings

See AGM-winning agapanthus

Find agapanthus suppliers

Buying agapanthus

• 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

In borders

Grow all agapanthus in well-drained soil in full sun. Avoid planting in shade as they won't flower as well. 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

These are fleshy, rounded, underground storage organs, usually sold and planted while dormant. Examples include daffodils, tulips, hyacinths, lilies, onions and garlic. The term is often used to cover other underground storage organs, including corms, tubers and rhizomes.

or fleshy rhizomes

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

, the noses should be covered with 5cm (2in) of soil. If your soil is prone to waterlogging, or you live in a cold area, consider growing agapanthus in containers.

RHS guide to planting perennials

In containers

Grow plants in containers at least 20-23cm (8-9in) in diameter, in a peat-free compost

Can refer to either home-made garden compost or seed/potting compost:

• Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

. All container plants (hardy or tender) benefit from some winter protection (see Overwintering in Ongoing Care section below).

Growing plants in containers

Watering

• Once established, agapanthus need little watering, but may benefit from some in late summer in very dry years as this will help ensure good flowering in the next year.

Feeding

• It is beneficial to feed plants in containers, as they have less access to nutrients
  

  To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth.

  than plants growing in the ground. Feed with an organic, liquid seaweed fertiliser throughout the growing season
  

  The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

  , following the instructions recommended on the packet.

RHS guide to feeding plants

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
  

  Deciduous refers to plants (mainly trees and shrubs) that lose their leaves seasonally, usually during autumn. This is a natural process triggered by the season's shorter days and lower temperatures and allows plants to conserve energy during the winter months.

  types in the autumn, as they natural die back. Tatty leaves on evergreens can be taken off at any time

Overwintering

• 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 biodegradable
  

  Anything that can be decomposed by fungi, bacteria and micro-organisms, so it doesn’t persist indefinitely in the environment. Biodegradable plastics are usually made from plants, such as bamboo, rather than fossil fuels. Ideally, products that claim to be biodegradable should break down quickly and leave nothing harmful behind. However, they may need specific conditions in order to biodegrade successfully or may produce greenhouse gases such as methane in the process.

  fleece
  

  A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops.

  for protection from November to early April. Containers can be wrapped with reused/repurposed bubblewrap or hessian to protect the roots.
• Evergreen plants and the more tender varieties do need winter protection. A few layers of biodegradable 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
  

  Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

  around plants in autumn or early winter and remove in spring before growth starts. For the mulch, you can use sand, home-made compost
  

  Can refer to either home-made garden compost or seed/potting compost:

  
  • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

  , chipped bark
  

  Bark is the outermost layer of woody plants (trees, shrubs and woody climbers). It is several cells thick and provides protection against physical damage, disease and environmental stresses. Bark comes in a wide variety of colours and patterns, and these can help gardeners when identifying plants. The fissures and crevices of bark on older plants also creates valuable habitat for many garden creatures as well as lichens and small plants.

  or straw

Overwintering tender plants

Overwintering plants in conservatories

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

Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.

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

A seedling is a young plant grown from seed.

.

Despite being easy to grow, agapanthus are occasionally subject to problems.

Agapanthus gall midge

Preventing winter damage

Plant viruses

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, avoid letting plants grown in containers dry out completely through summer until early autumn, as a lack of water can prevent the development of new flower buds.

Although often said, agapanthus don't actually flower better when pot-bound

Describes a pot-grown plant whose roots are filling the container, densely packed and intertwined. Check the roots of container plants regularly, and re-pot into a larger container before they become pot-bound, to ensure continued healthy growth. The roots of pot-bound plants are unlikely to spread out into new soil or compost without first being physically loosened.

. 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.