What is a weed?
It is a truism to say that a weed is 'a plant in the wrong place' but it is a simple and frequently accurate definition. In everyday circumstances, weeds such as dandelions, nettles, daisies, ground elder and chickweed are the unwanted plants that appear in our gardens and lawns. Poppies, cornflowers are unwanted plants in the fields of arable crops. When humans existed in hunter-gatherer societies, with nomadic life styles and no established agricultural systems then the 'concept' of a weed did not really exist.
In many cases, weeds are opportunists; they quickly colonise bare or disturbed ground. Often they are plants that can complete their life cycle (from seed to seed) very rapidly. Such plants are termed ephemerals, many can complete their life cycle in six to eight weeks, and therefore go through several generations in a year.
Hairy bittercress (Cardamine hirsuta) and chickweed (Stellaria media) are common garden weeds that can complete their life cycles in a matter of weeks. Bittercress is a common weed belonging to the Crucifer family - a group of plants that includes the wallflowers, mustards and watercress. Bittercress has small white flowers with 4 petals and 4 stamens (floral parts of fours is 'typical' of Crucifers). It is quick to colonise bare ground and garden beds!
Similarly, Chickweed can mature in 5/6 weeks (it can overwinter). It has a rather 'sprawling', untidy straggling pattern of growth. The flowers are also small and white, but the white petals are so deeply divided that a flower may appear to have ten petals. The sepals are longer than the petals. It seems to flower more or less all round the year. It is probably one of the most common weeds in gardens, though groundsel (Senecio vulgaris) might run it a close second. In the past, Chickweed was used in soups and as a garnish and it was included in the herbalists 'repertoire' to make infusions for rashes and sores and poultices to help reduce 'swellings'. Such weeds can be controlled by regular hoeing, hand weeding (though it is important to get the root as well as the stem and leaves).
Contact weedkillers, like paraquat or diquat may be used to control them but need careful application.
