[snowdrops]

You'd have to make your cuts very big to get over the plants. Thanks for every ones comments I'll come back later in the year & let you know how I get on.

You lay the covering on the ground, make X shaped cuts in it, peel back the flaps, and put the plant roots / tubers etc into the soil through the covering.  You don't put the plants in first and then waggle the covering over the plants.

No what I meant was in reply to

if i take the polythene off in the autumn once the plants have established themselves ,and the weeds have slowed down, do you think that would be ok for the soil

Thats when the crosses would have to be big to get over the plants 

[Yorkie]

Aah, see what you mean 

You may have a point!

[Brassica Blaz]

Standard polythene will not allow air or water through, and thus does the soil no good.  If you can get proper stuff then that would be advisable.

I would also advise that you take proper precautions against the cabbage root fly - i.e. the collars which you can get or make.  The fly will be able to lay its eggs through the cross you will have to make in the weed suppressant in order to get the plant in.

its just that i can get the polythene free and thought i would be able to utilize it without having to pay for weed suppressant.