Putting carpet over it would get rid of the weeds eventually but it takes a long time. I don't think sowing seed in a layer of soil over carpet would be very successful. It would be better to clear the weed and sow into the soil if you are in a hurry for your grass. You could use glyphosate weed killer but it would need several applications to deal with the horsetail and its not the best time of year to do it now growth is slowing- however if you keep the lawn well mown it wouldn't have the change to grow tall. If you use a total weedkiller instead of the glyphosate you won't be able to grow anything at all for at least six months. Nettles are quite easy to dig up as they have bright yellow roots which are easy to see. If the thistles have set seed you'll have them popping up all over next year though! Several options then, but none of them really easy!

Can I just ask will a childrens play are be allowed or even popular on an allotment?

Thanks for that Bilbo, I did wonder, its nice if they can join in or how do they learn.

You're right Bilbo - but recently there's been a massive increase in family involvement on London allotments, where allotments are available at all - whole families pitch up and work, have a bbq, and the kids help out as well as play. Great stuff, hope it gets to be a bigger movement, we need it.

Hi,
Thanks for the reponses so far.
My allotment at the St Anns allotment site in Nottingham.
Children are very welcome on the site, we have a community orchard which is run as an educational project with local schools.
We have very little restrictions on how the plots are managed by tenants.
Areas of my plot are rife with Marestail which I have tried to control over the last 5 years, using a lot of the ideas suggested. It is in desperation that I thought of covering over an area with sheets, and sowing grass directly over. Our plots are about double the size of an average allotment plot. I wanted to lawn part of it to use as a play area, whilst I fully tackled the weed situation on the other part.
If anyone is interested in St Anns Allotment (otherwise known as Hungerhill Gardens) please look at:
www.staa-allotments.org.uk or alterantively come along to one of our twice yearly open days.

Marestail in lawns can be kept in check by regular mowing. If you were to lay turf, then you could just keep cutting it once the grass gets about 6 inches in height. It'd still be there, under the turf, but regular cutting will prevent it from growing properly over the turf. From seed is much more difficult - by the time the seed's germinated and you're able to cut with a mower rather than shears, there may be prolific growth of weeds which will choke out the new grass seedlings.
Both thistles and nettles can be controlled in the same way, but I'd consider those a bit more of a nuisance - stingy things hidden in the turf where children play isn't great.

Thanks! Turfing sounds like it would help control the weeds, but I'm guessing a lot more expensive, How much approx per square metre?

Pass, don't know - varies from area to area round the country. I'd expect it to be cheaper where you are than in London. If you have Wickes, they sell turf at different times of year in some larger branches, so ring them and ask. Most prices online are for laying it as well as supplying it, I've just had a very quick look. Don't buy really cheap turf from a supplier who just supplies turf unless you know someone who's bought from them already - you don't want broken, thin or yellowing stuff to be delivered. Start with Wickes and then ring for quotes from anywhere you can think of.

I would say dig out the offending weed growth with its roots, pile up to dry, then burn on the spot, on days allowed in the Allotment Field Rules.
My cold compost bin is overflowing, so am doing this over the next few weeks to clear the ground before winter.