When spring time comes, your plants begin to grow again, and your weeds grow too. How can you be sure you're pulling up a weed and not the plant you had there last year? Here are some weed identification tips and resources for common weeds across the US.
Get to know the weeds in your area by viewing common weeds from www.weedalert.com. This is the best site I've found for easily identifying weeds based on where you live in the United States. Just click on your region and you'll see a list of common weeds with pictures. You can click on the pictures for a closer look and for information about integrated pest management. Another good site is the USDA Plant database at http://plants.usda.gov/java/noxiousDriver. You can look up common weeds based on the state or region in which you live.
Learn from your weeds. Some weeds grow well in acidic soil, others prefer clay, and other weeds thrive in wet or soggy soil. Knowing your soil conditions can help identify weeds because you can limit your search for weeds that grow best in your current soil conditions. Or, if you don't know what kind of soil you have, you can figure that out by noticing a common theme with your weeds that thrive certain conditions such as acidic soil. This website: www.primalseeds.org/weeds.htm provides a list of weeds with the soil environment they grow best in. You can use it to help identify weeds and also to learn how to amend your soil to make it less desirable for weeds.
Another site to look at is: http://www.beyondpesticides.org/pesticidefreelawns/resources/index.htm There is an article called "Read your weeds" that describes more about the conditions of your soil based on the kinds of weeds that are growing in it. There is also an article titled "Least Toxic Control of Weeds" as well as information about growing pesticide free lawns.
If you are unable to identify a plant after looking at the common weeds in your region, you still have a few options. Take a closer look at your plant and try to identify the leaf patterns. A good example of leaf patterns and weed identification is: http://www.gemplers.com/tech/iweedid.htm
Then look at seedling photos based on the leaf characteristics at: http://theseedsite.co.uk/seedlings.html or at http://wintersown.org/wseo1/Photo_Gallery_Portal.html
If you still aren't sure what the plant is, take a picture of it and post it to a garden newsgroup asking someone to id the plant for you. You'll likely get a fast and accurate response from someone willing to help you. GardenWeb's Name That Plant! Forum http://forums2.gardenweb.com/forums/namegal/