Successful weeds tend to be fast growing and colonize new ground rapidly. They should not be allowed to invade ornamental or food growing areas as they out-compete the plants we want to grow by depriving them of water, nutrients, and light. Understanding how weeds grow can help us to control them. Annual weeds survive long term by producing large quantities of seed before dying, while perennial weeds build up food reserves underground; not only do these reserves make perennial weeds harder to pull out, but they allow them to regrow when the top growth is killed. Always aim to remove weeds before they set seed.
Annual weeds usually have short, fibrous root systems so are relatively easy to pull out by hand. Their roots rarely survive if the leaves and shoots are killed, so removal with a hoe works well over large areas and between rows of vegetables. Move the blade parallel with the ground, cutting the tops off the weeds just below soil level. It takes immense persistence to control perennial weeds this way.
Digging can be a good way to clear taprooted perennials if you are careful to remove the whole root. Unfortunately, its very difficult to eradicate weeds with creeping underground stems, or storage tubers, by digging alone as any tiny pieces left in the soil will regrow.
There are many weedkillers on the market. Before you buy, check that the product is suitable for the type of weeds you want to kill and area you want to treat.
Contact weedkillers: These act quickly to kill the parts of the plant they touch. They are carried down to the roots so are only effective against annual weeds.
Systemic weedkillers: These tend to act more slowly, but they are carried down to the roots to kill both annual and perennial weeds. Selective weedkillers are effective against many broadleaved weeds, but do not affect grasses, so are ideal for use on lawns.