Allotments 4 All

If you till a plot that is infested with couch, then allow it to regrow a little, before re-tilling, then you accelerate the destruction of the couch by exhausting the rhizomes; the regrowth uses root stores, but if destroyed before photosynthesis begins then they are not replenished.

Anyway, if you cover a plot until the couch has died, then uncover until it grows a little, then recover, would this accelerate the rhizome distruction in the same way as outlined above and in doing so reduce the length of the time needed for covering to achieve its purpose?

If you cover a plot until the couch has died then by definition it can't recover, its dead and nothing on Gods green earth is immortal. In practice it is very easy to underestimate how resiliate these blighters can be and the plant will continue to grow under the cover looking for light, using the energy and nutrient reserves in its roots until it either finds light. If you really want to speed things up without using chemicals (I have a Ph.D. in chemistry so they don't bother me !) then you could try tilling, covering up and a couple of weeks later repeating.

It'll be trying to grow under the plastic anyway, so I don't think periodically uncovering it will make any difference. What is important is to dig a trench all the way round or dig the edge of the plastic in a few inches. If youy don't, any couch outside the covered area will be feeding the roots you're trying to kill.