Topic: What are weeds and what are not?

[antipodes]

OK I guess this is a novice question: How do I know what are weeds and what are not? Or rather, which weeds should I really attack with fervour and which can be just casually chucked out as you go along?
I can't really identify them, that's the trouble. I have looked at a couple of sites, but not too much success. I seem to have found a couple, I have cat's ear, a few thistle/dandelion types that pull out pretty easily, and some crane's bill (which I personally think is quite pretty.
There is some grass but don't know if it is couch  :( and something that resembles a type of clover, it spreads in a mat-like way and does seem to be a bit of a nuisance.
I would like to weed all around the edges of my little plot but I can't afford planks or things to border it off - can you think of any plants that could replace the weeds on the borders? Something about 20 cm high would be ideal, to keep the soil in place and cordon off.
So 2 questions: how do I identify weeds and what to replace them with in places where there are no crops.
BTW, I am using no weedkillers etc so weeds are either dug out or smothered.
Please help!! The plot is a fair bit clear but some parts are getting a bit over-run and my neighbours are making "wot a useless gardener" type faces...  ???

[Barnowl]

Couch grass has long white roots with what look like barbs in them. If that's what you've got you need to remove every bit of root - even the smallest bit will give rise to a new plant - so dig out carefully. I''ve had to follow the roots down over a foot before now.

Mares Tails / Horse Tail - as above re the roots.

This site may help:

http://www.gardenorganic.org.uk/organicweeds/weed_information/weedtype.php?id=0

[Barnowl]

By the way, a weed is anything growing where you don't want it to!

This is another site - weed descriptions and links on the right hand side.
http://www.dgsgardening.btinternet.co.uk/weeds.htm

[antipodes]

Thanks for those sites! they are pretty good, except you have to click a lot of links!
Pretty sure I have crane's bill, groundsel and a bit of fool's parsley.
the grass has me stumped. It tends to mat together so when I dig it up it is in a wide mat and sticks together. I have been shaking off the soil and chucking it aside to rot. An old fella gave me the tip of digging a bloody big trench and burying the grass! Now I did this is one area, as a test and I must admit, it seems to work, but it's too much hard work for the whole plot! The grass I fear will have to be smothered. The clover like stuff, I dunno
I will try and take some pics and post them.

[Barnowl]

If it's not couch, some people lift it like turf and make a stack of it, turned roots upwards , at one end of the allotment