Uneven, weedy lawn> weed membrane, new lawn?

Hi, i currently have a really uneven (can dip down up to 9inches in places) lawn filled with lots of big thick weeds and some grass...... im about to rotovate it picking out as many weeds as i can and move the soil into the dips and then roller it flat.
my question is, knowing that weeds will begin to grow back through my nice flat surface is can i put weed membrane down over the entire area and put 4 inches of good quality topsoil and then lay my lawn afresh?
if not what tips could you give me in regards to obtaining a nice flat weedless lawn given my mentioned circumstances. thanks.

INFO:

Lawn Area= 7m x 5m
50% weeds
10 year old New Build garden

THANKYOU!

 

Rather than roll it flat you need to "drag" it flat. Traditionally this was done using a Lute, but the easiest way nowadays is to get a ladder, put a rope around each end, add some weight to the rungs (e.g. breeze-blocks) and drag the ladder North-South and East-West and it will even out hollows-and-bumps.

No, your grass won't grow. Weeds aren't called Weeds for a reason" they will outgrow other plants. If you put down obstacles for the weeds so that you weaken them, then you will also weaken the plants you want to keep - such that the weeds still have the upper-hand.

You can sow seed, and try to deal with the weeds. Chemicals will help (but limited choice that can be used on New lawns (younger than 6 months, say)

Or you could lay turf (i.e. the grass is already formed), and thus weed competition is stymied. My personal preference is to sow grass seed in the Autumn - when the weeds are shutting down for the Winter. If you sow in the Spring you are giving Weeds and Grass seed an equal chance, so Autumn-sown germinates and sits there for the Winter and is thus better able to compete come the Spring :thumb:

 

ok thanks, but just to check that i was clear, if i was to lay a weed membrane over my old weed ridden lawn, then add 4 inches of topsoil on top of the membarane and then lay turf on top of the topsoil are you saying that the grass would not flourish due to the membrane underneath?
also if i was to lay turf over my rotavated and dragged flat garden, aren't the old weeds just going to grow through the newly layed turf, thus rendering it a waste of money? thanks for your help. J

 

its an ongoing battle. In a couple of years you will have new weeds in your turf - even if there were none there to start with. You have to use selective weed killer to get rid of them

If you are going to make the existing law flat, and then seed/turf it, you could use weed-killer to kill the weeds before you start. But there will be weed seed in the ground ... and the weed-killer probably won't kill all the weeds. But you can use a selective weed-killer to do that once the weeds start to appear. If you lay turf you probably won't get any / many this year in my experience.

If you put a weed membrane down and 4" of top soil then the new lawn has only 4 inches to grow in. Its not enough.

 

Just a thought weed membrane is water permeable and as grass has fine roots it may well grow into and through the membrane. I seem to remember being able to buy turf with a fine membrane and about an inch of soil roots then grew into the ground beneath. Long time ago so may have been a failure (probably too expensive )

 

That type of grass "seedling matt" is still available, as far as I know. Its an alternative to turf - as it doesn't require an inch or so of top-soil to be striped from the field when the turf is lifted, but I think its harder to establish.

 

I'm guessing you would only use it where special quality was need then and you had the time to give it attention. It makes sense about being harder to establish, less bulk less root more chance of drying out.