Annual weeds

Annuals are plants that germinate from seed, grow, flower and set seed, so completing their lifecycle, within one year. Some, such as hairy bitter cress (Cardamine hirsuta), do this in a couple of weeks or a couple of months, so several generations can appear each year. Some will also grow, and even flower, during mild weather in winter.

Generally annuals produce lots of seeds, and as these can remain dormant in the ground for several years – “One year’s seeding means seven years weeding” – allowing weeds to flower and produce seeds, sets you up for many years of weeding!

As any plant “growing in the wrong place” is regarded as a weed, cultivated plants allowed to set seeds and produce lots of young plants where they’re not wanted can be regarded as “weeds”.

Many of our weedy species are naturally-occurring or wildflowers, so make sure these don’t produce seeds, unless you need or want more plants to cover larger areas of your garden.

• Beds
• Borders
• Lawns
• Gravel paths
• Between paving slabs
• Waste or uncultivated ground

There is a huge range of annual weeds that will appear in our gardens. Some are more troublesome than others. It’s their ability to produce up to hundreds of seeds and seedlings if allowed to, that creates the problems and ensures we regard them as weeds.

Common annual weeds include the following

Annual meadow grass (Poa annua)
Annual mercury (Mercurialis annua)
Charlock (Sinapis arvensis)
Chickweed (Stellaria media)
Cleavers, goosegrass (Galium aparine)
Common purslane (Portulaca oleracea)
Fat hen (Chenopodium album)
Field pennycress (Thlaspi arvense)
Groundsel (Senecio vulgaris)
Hairy bittercress (Cardamine hirsuta)
Henbit (Lamium amplexicaule)
Scarlet pimpernel (Anagallis arvensis)
Shepherd’s purse (Capsella bursa-pastoris)
Sow thistles (Sonchus species)

As with most weeds, never allow them to become established, and certainly don’t allow them to flower and produce seeds. This will make it more difficult, and more time consuming, to fully control them. Early identification and eradication is important to stop them taking over the garden.

Annual weeds have simple and generally shallow root systems, so hoeing them, pulling or digging them up is usually enough to control them.

Regularly hoeing seedlings and young plants as soon as you see them is the quickest and easiest method of control. The aim of hoeing is to sever the weed stems at or just below ground level, cutting the top growth from its roots. A sharp hoe blade will make this even quicker and easier, so always sharpen the hoe blade before using it. Hoeing on a warm and/or windy day will mean the weeds quickly dehydrate and die. Hoeing during cool and wet weather can allow some weeds to re-root.

Digging out the plants when they are more established is more time consuming and more difficult – especially where they’re growing among wanted plants.

Flame guns and weeders that use an electric current to dehydrate the weeds are also effective on annual weeds.

Covering bare soil with weed-control membrane (landscape fabric) or even thick black polythene will exclude light and prevent weed seeds from germinating. As will mulching the soil with organic matter, such as a bark mulch. For mulches to work properly, they need to be a minimum of 5cm (2in) thick, but 7.5cm (3in) deep works better.

In lawns, regular feeding and mowing throughout the year should prevent annual weeds from getting established in the first place, or control them if they do.

There are a number of weed control options available to treat annual weeds. In addition to traditional weedkillers there are now also a range of more natural alternatives.

Any weedkiller can be used to control and kill annual weeds. Those marketed as “fast acting” are contact weedkillers – killing or damaging the plant tissue they are sprayed onto or make contact with. These tend to be based on “naturally-occurring” active ingredients, such as acetic acid and natural fatty acids.

Systemic weedkillers, that also kill the roots can also be used on annual weeds.

To ensure weedkillers work more effectively:

• Spray the leaves when the weeds are growing actively; this is mainly from March/April to September/October. Contact weedkillers will have some effect if used during the colder weather in winter.
• Use a fine spray to thoroughly coat the leaves in small droplets.
• During the summer, spray in the evening to prevent the spray evaporating and to give maximum time for the spray to work. In spring or if overnight dew is forecast, spray earlier in the day to allow the spray to dry before dew falls.

Most weedkillers (except lawn weedkillers) are total weedkillers – that is they will damage or kill any plants whose leaves they are sprayed onto. Make sure you keep the spray off wanted plants – including lawns – and, if necessary protect plants by covering with polythene or similar when spraying.

Use weedkillers safely. Always read the label and product information before use.

Never allow plants to flower and set seed. Although this should be pretty easy in your garden, it’s more difficult to stop seeds blowing in from a neighbour’s garden, any surrounding fields and waste ground and even further afield.

• Spade
• Fork
• Hand fork
• Weeding tools
• Hoe
• Weed-control membrane
• Weedkillers
• Lawn weedkillers