For evergreen varieties, you should think about dividing and transplanting agapanthus every 4 to 5 years. Do the actual division when new growth emerges in spring, or else in early autumn after the plants have finished flowering. This timing works for deciduous plants too.
Dividing and transplanting agapanthus
However, if left untouched for any length of time, they will become overcrowded and may flower poorly. Lifting and dividing agapanthus every 3 to 4 years will promote better flowering.
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.
You may need to use two garden forks back to back to divide very established clumps. This can be done in spring or after flowering in autumn. Agapanthus species can be grown from collected seed but the cultivars will not come true to type.
During the summer, you can help the plant conserve energy by removing spent flowers. Cut back the flower stems all the way to the base of the plant. Deadheading prevents the plant from going to seed and helps the plant store energy in the rhizome.
If you have a deciduous Agapanthus that you plan to keep outdoors over the winter months, then it is usual to cut back the stalks with spent flowers or seed heads (if these have not already been deadheaded) to around 10cm above the ground.
Ideally you should split and divide your agapanthus every four to six years. Agapanthus can also readily be propagated by seed. If you grow several different named varieties in your garden do not expect the seedlings to come true.
Deciduous varieties – Cut back agapanthus stems to about 4 inches (10 cm.) above the ground at the end of the blooming season. However, if you like the texture and structure that spent plants provide to the winter landscape, cutting back agapanthus can wait until early spring.
Dividing agapanthus
The best time to divide agapanthus is late March to April, before the flowering season. Lift the plant out of the ground and split the root clump with a sharp spade or two forks back-to-back, making sure each of the new clumps has at least two growing points. Then simply plant these out as usual.
This plant can be easily propagated through division in late autumn to winter by carefully removing it from the ground or the pot. Gently shake off some of the soil so that you can see the roots and the individual plants. Carefully pull the individual plants apart making sure that each one retains its own roots.
Every two or three years you need to dig up your agapanthus and divide them. You can tell they need dividing if they are flowering less over the summer as they maybe too cramped and need more space to shine. Do this in autumn or early winter.
In indigenous gardens, agapanthus are perfect companions with summer-flowering bulbs of crocosmia, galtonia, eucomis and watsonia. Agapanthus are also striking with sedges or phormiums, such as 'Yellow Wave', and eye-catching among whispering ornamental grasses.
Avoid fertilizing your Agapanthus plants with high nitrogen fertilizers - use instead a balanced fertilizer such as 10-10-10 or 5-5-5, or slightly higher in phosphorus than nitrogen. Suspend any fertilizer to either potted or in-ground plants by late summer.
To restrict its spread from your garden, deadhead stalks as flowers finish and don't dump unwanted plants. If you have a mass planting of agapanthus, deadheading sounds onerous, particularly for a plant that's often grown for its low maintenance.
It is a perennial plant that can live for up to 75 years. Its evergreen leaves are 2 cm wide and 50 cm long. Its inflorescence is an umbel. The flowers are blue, purple or white and bloom from late spring to summer, followed by capsules filled with black seeds.
Most Agapanthus bloom for around 6 weeks, however 'Flower of Love' has been specially bred to be much more floriferous than other varieties, for an incredible 10-12 weeks, starting around mid-July.
Agapanthus grows and spreads by fleshy rhizomes that act as storage roots. The plant retains nutrients in its roots and may be divided to create more plants. Use a sharp shovel to dig up an established plant and divide it into several sections, each with roots and foliage.
Agapanthus are easy to propagate by division to obtain plants identical to the parent plant, this is best done between spring and early summer. Avoid splitting plants too often as this will reduce flowering. Large clumps in the border should be lifted in spring every 4 - 6 years and replanted.
Every two to three years, you may need to repot your plants into slightly larger containers because although they like being a bit root bound, they'll appreciate a fresh potting mix and a bit more room to grow. As a rule of thumb, aim to repot into a container that's two inches larger in diameter than the existing pot.
As soon as these first blooms begin to die back, and before they go to seed, you can start deadheading. Then, as required or desired, you can continue to deadhead all through the rest of the summer and into autumn. However deadheading is not necessary if you'd prefer to acquire some seeds for use in future years.