You can dig up the agapanthus anytime throughout spring, summer and fall, even when the plant is in bloom. You can cut back the foliage to make the plant easier to handle, if desired; the foliage grows back after transplanting.
Most authorities confirm that agapanthus is very difficult to get rid of, even with powerful sprays. Common recommendations are for glyphosate, metsulfuron-methyl (MSF600) and triclopyr (Triclo).
Generally 3-4 inches deep for the larger variety and about 2 inches for the dwarf varieties.
Dividing and transplanting in the garden
The best time to do this is in autumn. To make the plants easier to handle for lifting and division, cut the foliage back and dig around the perimeter of the plant keeping the spade or gardening fork at least 140mm out from the plant basal area and to a depth of about 200mm.
Get cleaning: The important bit to remove is the rhizome, don't worry too much about getting all the white wriggly roots. It's the rhizome that will resprout and grow more agapanthuses.
Established clumps can be lifted and divided into smaller clumps. Spring (late March and April) is the best time to do it.
Because agapanthus plants spread quickly, they are regarded as an invasive weed in parts of New South Wales and Victoria.
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.
As the plants mature, they crowd against each other underground, and this overcrowding limits their flowering. The best way to remedy the problem is to start dividing and transplanting agapanthus.
Agapanthus plants benefit from regular deadheading, which helps them conserve energy. Simply remove the entire flower stem once the blooms have faded.
Agapanthus roots are a good example of a plant with a good ability to withstand drought and poor growing conditions due to its large, fleshy roots.
We take a responsibility by highlighting that Agapanthus can be considered a noxious weed in certain locations, and advise customers to consider their local area before purchasing, and at the same time we continue to source a better range of Agapanthus including sterile and low risk varieties that don't self-seed ...
Give agapanthus lots of sun, plus extra water when its really hot and dry and they'll bloom abundantly. Agapanthus plants that fail to flower are usually growing in too much shade. While they grow with little care, agapanthus plants respond to an application of fertiliser or composted manure in spring.
For the garden, my choice would be the Tasman Flax Lily (Dianella tasmannica). The smooth, shiny leaves are almost as large as the agapanthus and as the plant matures it sends runners out to the side that makes a very nice clump just like an aga.
Pot-grown agapanthus will benefit from an annual feed – a liquid tomato feed is ideal. Deadhead spent blooms to encourage more to form, or leave the faded flower heads in place if you want to collect the seed. The attractive seedheads are often left on over autumn for decorative reasons.
Tender or potted agapanthus should be moved into a sheltered location where they will be free from frost (do so before the first frost in autumn and move back after the last frost in spring). An unheated greenhouse or even the base of a sunny wall may be suitable.
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.
Agapanthus lilies are probably of minimal toxicity to animals unless eaten in quantity. However, where a dog or cat is prone to chewing on plants, it would be prudent to remove the plant from the animals environment.
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.