How do I totally kill off all the existing grass in a field, so that I can re-level and eventually reseed it all? Martin Mackay of Ireland

Dear Hugh, I visited your uk garden designer web site, very interesting. I have bought a 2 acre plot in west Ireland, my house is under construction and I am planning the garden already. I want to totally kill off all the existing grass eventually, re-level all with a plough/digger and eventually reseed all. The field was once used for young calfs and is very weedy. Can that be done. Sprayed to kill off? Left for a while? Then turned over to rot away? That is my best guess. We have excavated spoil for a large natural pond at the bottom lowest end where the land slopes away. I am considering using bentonite clay or a EPDM Firestone liner to manage the water retention. Your advice on the grass question would be helpful, if you know any good sources of info for me to better plan that stage I will be very grateful. I work in France in the winter and will be doing all the interior house building as well as the grounds. I am planning to turn our new house into a very desirable property, the grounds must be neat, hence my love for level neat lawns.
Forum (Hugh):The best way is to use a weed killer called Roundup or glypsophate. Your farming neighbours should be able to advise as to where to get it from, and which contractor to put it on. This chemical is broken down by the soil bacteria-so it leaves no residue in the soil. It is active in good light conditions, therefore it ‘works’ from April-September, you have to wait until April before you can spray. The chemical takes three weeks to work. Do not plough, allow the secondary growth to grow-you will probable get thistles, and other weeds, spray again on the advice of your contractor as to which chemical for thistles, you could follow this up with another application. When the ground is clean plough in the autumn-it is easer to plough clean ground-grass is not killed by ploughing and the sward leaves a mess making it harder to till afterwards. Your agricultural contractor should be able to advise as to cultivation.
For the pond butyl is the best liner with a 100 year guarantee. Clay has the disadvantage of having to be kept wet-if it dries it cracks-and you lose all your lovely water, this can occur when the water evaporates around the margins. Once it cracks it can’t be repaired. Also roots can grow through it-whereas butyl will stretch. Therefore it is worth the extra expense. Hope this helps, come back if want any more information.
I will pass your enquiry for Butyl to my supplier-they will contact you. They will need to know the size of your pond-they can advise as to depth but 1m should be sufficient. You should also be able to get it in Ireland-but these are big suppliers who work overseas as well as the UK. Yes leaving the pond natural is the best way-it will need planting with oxygenating plants, and should have as much sun as possible. If you are to use a digger don’t plough first. Soil structure can be easily damaged by over working especially in wet conditions. Keeping it un-worked until you require it is the best way, shape it once if possible, and let the result settle. Doing it in the summer months when it is dryer is best, after settling cultivate with a power harrow, level, and allow to go stale. Let the weeds grow and spray off – this is all helping to clean the ground for your lawns. (the problem is not only the existing weeds, but the seeds accumulated in the soil from other similar weeds over the years-one year’s seed, seven years weed). Sow grass on your prepared lawn areas in early Autumn – September with a lawn mix, in the next year-or the Spring of that year.