Common Ragwort is usually considered to be a biennial, over-wintering either as seeds or as rosettes. It is also capable of becoming a short-lived perennial if the flower stem is cut (eg. in the lawn), but usually it dies after producing seeds. The leaves are light to dark green and deeply lobed. The lower leaves form a rosette which is present from autumn to late June and dies back when the main stem develops before flowering starts in late summer of the second year. It grows 30-100 cm high with woody stems which are red at the base. The upper part of the stem is branched and bears yellow flower-heads in large dense flat-topped terminal clusters, nearly always rayed, and daisy-like. A single plant can produce over 150,000 white downy seeds, which are carried away by the wind, and which can remain viable in the soil for up to 15 years.
The foliage is attacked by the caterpillar of the Cinnabar Moth and they have been used as a biological control.

In folklore it was believed that the fairies used Ragwort to ride around the world creating mischief.

All parts of the plant contain alkaloids that are toxic to cattle, deer, pigs, horses and goats, causing liver damage, and death is slow often occurring months after ingestion. Sheep are less affected, but should not consume the weed as the liver damage can be cumulative. The foliage has a distinctive unpleasent odour when crushed so poisoning by grazing on living plants is rare as it is instinctively avoided. If the plants are carelessly cut or uprooted and left around to wilt, they become palatable as the distinctive smell fades but the alkaloids are still potent, so grazing animals can be poisoned.
It is possible therefore for dead plants to be incorporated into silage or hay and this is the main cause of Ragwort poisoning. Great care must be taken to avoid this happening. The flowering stems should be developed when the forage is being saved, so any plants are easily spotted before cutting commences.
Cutting or hand pulling in the early stages of growth leaves the root of the plant to regenerate. Gloves should be worn when handling the plants as crushing them releases the sap which can be absorbed through the skin and as with livestock the toxins are not excreted so build up in the liver.
Digging up the root is best, but complete removal is necessary. If pulled when in flower it is rare for the plant to regrow as being monocarpic, it is due to die soon anyway.
In grazing or in the lawn spraying works if done during the rosette stage in the spring using a selective herbicide such asMCPA or 2,4D. As the plants become palatable when dead, grazing animals should be kept out of treated areas until they have rotted away or been removed. They are easily uprooted from flowerbeds, but in paving crevices it might be best to use something like Glyphosate.
Ragwort is an injurious weed and is specified in the Weeds Act 1959. The M.A.F.F./ D.A.N.I.(or whatever it's called now, our present government squanders millions changing the departmental names almost yearly!!) has powers to serve clearance notices but will only do so where agricultural production is directly affected. On roadside verges and waste land, local authorities should be contacted.

See also Oxford Ragwort and Groundsel which have similar leaves and flowers.

Silver Ragwort (Senecio cineraria syn. Cineraria maritima), a perennial subshrub, is a close relative. It is usually called Cineraria and is used for its 'silver' foliage in annual bedding plantings. If allowed to develop, in subsequent years it will produce upright stems with flowers very similar to those of Common Ragwort. When growing in close proximity the Common and Silver Ragwort can hybridise.
In North America the Annual Ragweed, Ambrosia artimisiifolia, is a completely different plant, and the pollen it produces is a major cause of hayfever. The foliage is fern-like and the flowers are borne on spikes. (also known as common ragweed, low ragweed, ragweed, Roman wormwood, short ragweed, small ragweed).
Giant Ragweed, Ambrosia trifida is a perennial with palmate leaves bearing three to five deeply cut lobes. (also known as blood ragweed, great ragweed, horseweed, perennial ragweed (great), tall ragweed)