purslane, nettles, dandelions), many are a nuisance and compete with your chosen plants for water and nutrients.
Whichever variation of “One year’s seeds makes seven years’ weeds” you prefer, the truth remains: a key part of weed control is not letting them go to seed. For best results, work on removing weeds before they are able to propagate. Hand pulling and hoeing are effective methods for killing many common weeds.
Knowing what kind of weeds you have can be helpful in choosing the best management method. If you want to know what a weed is called or how it propagates, check into online resources or UC's Weed Gallery. If they propagate by seed, pull or hoe them before they flower and go to seed. If they re-grow from roots, pull up as much of the root as possible. Many weeds, like Bermuda grass, have multiple ways of multiplying. Only non-propagating parts are advisable to throw in the compost bin.
More Information: UC Pest Note on Weed Management in Landscapes