The bright lemon yellow flowers of greater celandine ( Chelidonium majus ) quickly fade, leaving long thin seedpods packed with seed. This common garden weed has a long history of herbal use but the distinctive orange sap is an irritant. Common yellow woodsorrel is a low-growing weed found throughout most of the US and almost all of Wisconsin. It can be a problem in gardens and lawns. Learn more about this species in this article…
The bright lemon yellow flowers of greater celandine (Chelidonium majus) quickly fade, leaving long thin seedpods packed with seed. This common garden weed has a long history of herbal use but the distinctive orange sap is an irritant.
Common name Greater celandine, swallow wort
Botanical name Chelidonium majus
Area affected Garden borders and grassland
Caused by Readily self-seeds
Timing Flowers May- August; treat from spring to autumn
What is greater celandine?
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.
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.
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.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)
Common Yellow Woodsorrel, Oxalis stricta
Common yellow woodsorrel.
Common yellow woodsorrel, Oxalis stricta, is a native North American plant (also found in Eurasia) which is usually considered a weed. It has numerous common names, including common yellow oxalis, sour grass, shamrock, sleeping beauty, sour trefoil, and sheep’s clover. It also has many synonyms: Ceratoxalis coloradensis, O. dillenii, O. europaea, O. prostrate, O. rupestris, and Xanthoxalis florida. It is found in 46 states but is most numerous in the eastern U. S. and into Canada. This species differs from other wood sorrels by being more erect, the stems grow at a sharp angle (about 90º) from the main stem and the seed pods bend sharply upward on their stalks.
An infestation of common yellow woodsorrel.
Common yellow woodsorrel is distinct from other wood sorrels in that the seed pods bend sharply upward on their stalks and the stalks also grow at a sharp angle from the main stalk (both angles are about 90 degrees). It also tends to grow in a more upright fashion than other wood sorrels (stricta means “upright”).
This herbaceous plant may grow either as an annual or as a weak perennial. Although it prefers moist soil, and partial shade, it is tolerant of a wide range of conditions. It is commonly found in fields, woods and borders, along roadsides and in other waste areas, and will even grow in the cracks of sidewalks.
Common yellow woodsorrel in a lawn.
It is also a common summer annual in lawns. As one of the latest germinating annual weeds, it often fills in spots left in the turf after broadleaf weeds are killed by early spring herbicide applications.
The delicate-looking plants grow 6-15″ tall – unless they are mowed off consistently in a lawn. They may form colonies arising from slender but tough underground stems (rhizomes), but more often are individual, seed-grown plants. The weak stems branch at the base and sometimes will root at nodes.
The trifolate leaves have heart-shaped leaflets.
Leaves are alternate, smooth and palmately compound. Each leaf is divided into three heart-shaped leaflets similar to a clover leaf, with faintly hairy margins. The leaves are creased and fold upward in half at night or when stressed (such as if picked or during storms). Most plants are green but some have a purple cast.
Common yellow woodsorrel has yellow flowers with five petals, which are followed by erect seed pods.
The yellow flowers have 5 petals that are held in an open cup up to ½” across on a long stalk. They occur singly or in axillary clusters of up to five flowers. Blooms first appear in mid spring and continue through fall. The flowers are followed by elongated, ridged seed pods that are pointed at the end. The erect seedpods are held at right angles with their stems. Each ½-1” long capsule has five compartments with about 10 seeds in each compartment. When the pods are ripe, they dehisce (open explosively at the slightest touch), launching the seed as far as 8-10 feet.
A common yellow woodsorrel seedling.
The leaves, flowers and unripe fruits are edible, with a sour, tart, lemony flavor. They can be added to salads, soups, or sauces, or used as a seasoning. However, it should be consumed in moderation because the plant contains rather high levels of oxalic acid which is toxic in excessive amounts. It should be avoided by those with kidney disease, kidney stones, rheumatoid arthritis, or gout.
Common yellow woodsorrel is best controlled by hand weeding and mulching. It pulls up quite easily and does not resprout from roots left behind. Try to remove plants before seed pods develop – although this may be difficult as it is good at hiding among other plants, producing seeds before it is ever noticed. Most herbicides are not very effective on Oxalis species. Pre-emergence herbicides, which prevent germination, are the most useful.
– Susan Mahr, University of Wisconsin – Madison
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