prepping new veg bed with black plastic

If its couch grass then I'd suggest covering it and then attempting to *remove* it when you lift the plastic - I suspect that 2 months would be enough to weaken it but not kill it - if its not dead when you rotavate it then you are chopping it up into more and more viable little bits and will give yourself a load of grief gong forward.

should I spray with roundup first ?

its a matter of personal choice - i generally don't use weedkiller on ground I'm going to use for food - but many are happy using roundup as it breaks down after use. I've found that it isn't necessarily that great against couch grass anyway.
This is what couch / twitch grass is / looks like:
https://www.rhs.org.uk/Advice/profile?PID=283
and its the rhizomes that spread it rather than seeds (generally speaking0
so it is couch grass its probably not a good time for roundup.

I've found that covering it for a few months does make it much much easier to then weed out - that is what i'd do though I appreciate it sounds like hard work - but once its weakened i've found it pretty easy to pull out

All sorts of approaches are possible - a lot of it will be a trade-off between time, money and effort with you being the only person who can decide what might work best for you.

As a for example, it is possible to more-or less completely clear a piece of ground of perennial weeds like couch just by using a rotovator, especially if the soil can be kept dry. Going over the same area every week or so for a few months in the growing season would do the trick, particularly if the ground can be covered up to keep the rain off between whiles. The down side of this is that you will be heartily sick of the sight of the rotovator by the end of it and the cost in petrol, maintenance etc will mount up. On the other hand you wont be putting any chemicals on your growing area and compered with the effort entailed in forking out all the weeds, it will almost certainly take less time as a total.

^^^ if you are going to rotavate then I agree with Nick - you have to do it a *lot* - doing it only once or twice will just lead to trouble

(this is all assuming that its couch grass we're talking about)

I don't know how big an area you want to cover but I would neither weedkill it or rotavate.

Mow the grass first - keep the grass cuttings.
Cover the area with wet cardboard, several layers, to stop the grass growing back.
Pile on top of the cardboard your grass cuttings, compost, manure, shredded paper, leaf mould, whatever you can find. You need a thick layer.
Plant into it.

There are lots of videos about this - Charles Dowding's No-Dig is a good place to start.

I have put black plastic down this morning and plan to put my potatos which are in 30 litre pots on top once the weather has warmed up , they are in the green house at the moment

They can be on there until they are all harvested at which point my intention is to lift the plastic and rotovate the compost that was in with the potatoes into the soil and use next year

I have set some rocket and pentland javelin in this way for this year

Hi Billy

I've got 3 plots, the first was easy as it was well looked after when I took it over.

The second was a beast as about a third had been dug at the front but the rest was full of everything, even an orange wheelbarrow you couldn't see (photo attached).



The grass and weeds (including brambles and nettles) were my height and I'm 6ft, I forget how many times I went home scratched and stung and lay in the bath nursing my wounds. (Hope this hasn't put you off) I tackled it with a brush cutter to chop everything down to the ground and cover with black plastic to weaken, then fire later to kill it all and use as fertiliser (we are allowed fires if so long as you use common sense and check the wind direction) which also helps clear the soil so I had about 4-5 of them over the same weeks. No rotavator yet, it was tempting but no as the ground needed to be dug with a spade, I dug out the first row and moved the soil to the back of the plot then cut the next row and turned it over into the first rows trench. No attempt to remove weeds or roots unless they are obvious, the weed tops die as fertiliser and you are left with another trench to put the next row in. I ONLY did 6 rows at a time, any more and you will feel it and there is no point trying to kill yourself and get it dug any faster. Only after you are finished should you then go back to the start and rotavate and remove the roots brought up as you go. Then you can plant, I mainly planted spuds in the bad 2 thirds which did well but the front thirds which was better had soft fruit planted in it.

The third plot is next door, had 6 trees on it which I chopped down and brambles which were almost as thick as a small tree trunk which is no kidding. I've prepped it over winter and everything has been removed (including the trees) and burnt, half has been covered in plastic over winter and is bare but still needs to be dug over before I get the rotavator on it to plant my spuds. In the following photo you can see the trees on it on the right of plot 2.



You can also see what is possible, just tackle it sensibly and you should be able to whip it into shape in a few months ... good luck and don't worry that you seem to be getting nowhere fast just a small progress at a time soon adds up.

I'll be creating a post about my progress with plot 3 shortly.

thats hard work and dedication but very satisfying at the end

I am with veggiechicken on this one. When you get your potato harvest in and put the spent compost on the ground you could put it in a layer along with grass clippings, leafmould, maybe a bag of manure, compost, any organic matter and cover it right up again with plastic until the following year when you just lift the plastic and plant.