Greater celandine or swallow wort is supposed to start flowering when the first swallows arrive and it’s botanical name Chelidonium is derived from the Greek for swallow. It is a member of the poppy family and, despite also having yellow flowers, is unrelated to lesser celandine (Ficaria verna subsp verna).

This perennial plant is possibly native but is rarely found far from habitation, commonly being found in both garden borders and rough grassland, where it can become quite an invasive weed. Bees pollinate the flowers of Chelidonium majus, and as it can potentially flower from late spring through to late summer, it can be a useful addition to a wildlife garden. This page looks at options for gardeners when greater celandine is becoming a problem.

Its 4-petalled, yellow flowers, individually short-lived, are borne in terminal groups of three to five and held above greyish-green leaves, from May through to late summer. Seed pods is are cylindrical 3-5cm (1¼-2in) long containing black shiny seeds with a translucent appendage.

Height to 75cm (29½in) and both stems and leaves exude orange latex when cut or damaged which can be an irritant.

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner. 

Cultural control

Can be controlled by cultural methods such as hand-weeding or hoeing seedlings. Larger plants may need lifting with a trowel or fork and should not be allowed to flower. Mulching with bulky organic matter or opaque films will also be successful.

Weedkiller control

In borders

As this is a perennial weed a systemic herbicide such as glyphosate is needed to kill the roots, as well as the foliage. Glyphosate is a non-selective, systemic weedkiller applied to the foliage. It is inactivated on contact with the soil, so there is no risk of damage to the roots of nearby ornamentals. 

Glyphosate is most effective when weed growth is vigorous. This usually occurs at flowering stage but before die-back begins; with most weeds, this is not earlier than midsummer. 

As glyphosate is not selective in its action, it is essential to avoid spray or spray drift coming into contact with garden plants. If treating weeds in the immediate vicinity of garden plants, apply carefully using a ready-to-use spray formulation in cool, calm weather. Branches or shoots can be held back, using canes, or by covering or screening while spraying, but make sure that the weed foliage has dried before releasing branches or removing the covering.

Used with care, glyphosate is safe to use around the base of non-suckering woody plants, as long as the bark is woody, brown and mature.  

In rough grassland

If the weed is growing in grassy areas, then the herbicide SBK Brushwood Killer can be used, as this would leave the grass unharmed. This again is systemic, working its way down from the foliage to the root system. SBK will damage any broad-leaved plants however (e.g. wildflowers) and so should only be used in grass where such action is acceptable.

Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)

Links

Chemicals: using spot and broad-scale weedkillers
Chemicals: using a sprayer
Chemicals: using safely and effectively
Weeds: non-chemical control