vegetable patch management
keeping couch out
If you have Couch grass in the lawn next to your vegetable patch it is vital that you create a barrier between your beds and the Couch grass, otherwise it's runners  will spread into the vegetable patch. There are three methods I have used which have proven successful in preventing Couch grass from infesting vegetable beds.
trench method
Illustration of a trench used top keep Couch grass out
Dig a trench along the edge of the lawn to keep Couch grass at bay.
Couch grass is a shallow rooted plant. If you dig a 10 to 12 cm (4 to 5 ") deep trench along the edge of the lawn it will act as a barrier between your vegetable patch and the couch grass.  The ideal tool for digging the such a trench is a simple spade.

But in order for the trench to continue to be an effective barrier it has to be regularly scoured with a hoe and the Couch grass at the edges trimmed back.  You may also have to re dig the trench with a spade if it gets too full of dirt.  I have found that the hoe is the best tool to scour the trench while sheers will handle the cutting of the Couch grass edges.  If you have a brush cutter than it is the ideal tool for both cutting the edges and lightly scouring the trench at the same time.

grass barrier method
Illustration of removing Couch grass laced soil
Remove Couch grass laced soil with clean soil.
Illustration of grass being used as a barrier against Couch grass.
Plant the clean soil with another type of awn grass seed.  Once established this grass will act as a barrier between the Couch grass and your vegetable patch.
While Couch grass will easily push through the loose soil of a vegetable bed it has great difficulty getting a foothold in an established lawn of a different grass species.

To establish a grass barrier between Couch  grass and your vegetable patch dig up the Couch infested soil some 30 to 40 cm (12 to 15 ") out from the edge of the garden bed and to a depth of below the bottom roots of the Couch.  Then replace the removed soil with clean soil and seed it with another type of grass.  Once established this new grass will act as a buffer between your vegetable bed and the Couch.  Just make sure that the lawn grass seed you buy does not have any Couch seeds in it.

galvanised roofing iron barrier
Illustration of a galvanised iron Courch grass barrier
Galvanised roofing iron pushed deep enough into the ground will act as an effective barrier against Couch grass.
The thinness and strength of galvanised roofing iron and the fact that it comes in wide lengths means that it can be driven deep into the ground with the use of a mallet.  Note though that if the ground is hard you may have to dig a partial trench to get it started.

All you have to do is make sure that there are no gaps where there are joins or at the corners for Couch grass runners to sneak through.  Even the smallest gap will offer an opportunity for Couch to get through. 

For more information on constructing raised beds using galvanised roofing iron see Raised Bed Materials in the Vegetable Patch Design section.