Weed barrier plantings for cold to temperate zones?

I see Mollison suggesting canna and lemongrass plantings around gardens to block invasive weeds from spreading in.
There are weeds around my place that could really use a good thick barrier as well! Any ideas?
I likely need about 120-150'.... I guess it gets really expensive if you need to buy plants doesn't it?
Thanks for any ideas!

some folks use comfrey this way. just have to be sure not to disturb the roots. some folks use bunchgrasses, though I never have. bunching bamboos would work, though they are quite expensive.

what are you trying to keep out? the strategy could change depending on the weeds involved.

Thanks for the reply.
Trying to keep out canary reed grass, super invasive yet shallow rooted. Mollison mentioned how tropical weeds were pretty awful so maybe they are as bad as CRG.
Comfrey is a good idea- I'm guessing it spreads if you damage the roots? It spreads quite well for me without any fiddling- however maybe just hoeing around the edge of the barrier monthly will keep it from encroaching. Hmm. Weeds.

Yeah, comfrey will most likely spread if you damage the roots.

Consider looking into Canada Lilly plant for your grass barrier. Around here they grow wild along roadsides, and they're also planted as an ornamental

maybe a double layer
Canada lily on the inside next to where you might be digging
comfrey on the outside next to the grass
both are pretty determined growers and will keep each other in check

Canada Lily {Lilium canadense) also has edible bulbs.

http://www.illinoiswildflowers.info/savanna/plants/canada_lily.htm

http://www.pfaf.org/user/Plant.aspx?LatinName=Lilium+canadense

Bulbs our great for keeping the weeds out: garlic, flowers (lily), and even onions. Last year I used a comfrey in one corner of my garden, but it got really large so I used taller flowers such as lemon balm or black-eyed susan to provide some break between weeds and garden area.

Since it is shallow rooted, you can just use wood ash. Will make it too alkaline to plant most anything else right there, so use a thin line of it, then plant something else just to the inside.

I like wooly thyme, especially cuz the oil from it will kill MRSA.

Essential oils will be big business in the future. Need a perfumers still to get it out tho.....