Cow Parsley is most commonly seen along the roadside where it forms a white, waving ribbon when it is in bloom in late spring and early summer. Other places to find it are at the edges of woodland and other shady places. It can be an annual to a perennial and is a member of the Carrot family so it may well be an alternate host for Carrot Root Fly which could be the reason the crop is always under attack. In fact there is an old gardening practice of sowing carrots only when the Cow Parsley is not in flower, ie. before the flowering stems develop or after the flowers fade. This timing avoids the two important generations of the fly. Apart from this it is not usually a problem weed in the garden.

As a herbal remedy it has been used to treat kidney and bladder stones, like others of the wild and cultivated parsleys. However, identification should be confident as the leaves of Hemlock, Conium maculatum are similar, but the unpleasant smell and the purple spots on the stems of the latter, make it quite distinctive.

The bright green leaves start to emerge in early spring and they have a slightly downy covering. They are 2 to 3 pinnate which means that the leaflets are divided to give a fern-like appearance. The stems are hollow with a furrowed surface giving a ribbed look, and can turn an overall purple as they mature, but not spotted. When in flower the plant can be up to 100cm tall.

The pure white flowers are borne on thin stalks in umbels 20 to 60 mm across with the individual flowers 3 to 4mm across. The fruit are long and smooth, turning a brown-black colour as they mature.

There are other Umbellifers which are similar, eg. Hedge Parsley (Torilis japonica) which grows along roadsides as well. Distinguishing features are the hollow stems of the Cow Parsley and the fruit of Hedge Parsley are round with a covering of curved spines. The latter also flowers later from July to August. Ground-Elder and Common Hogweed are in the same Family and has similar flower heads.

There are long taproots which should be mainly removed. Frequent close cutting will kill the plant - it survives on roadsides as they are usually cut once or twice a year. A translocated weed killer such as Glyphosate will work.