Wouldn't that still require me to dig out the roots one-by-one? Sorry, I'm new to gardening.

No you won't need to dig out the roots. The roundup will kill the whole plant. Some plants may have enough reserve energy to resprout, and may need a subsequent application, but once the plants are dead, the roots will rot up and feed the soil.

+1. It fails on some plants (like nutsedge) sometimes as the plant can re-sprout from inactive storage roots, but grasses and most weeds drop dead in a few days and you won't be seeing them again.

Warning--it'll kill anything you spray it on, so definitely avoid any plant you care about!

Round Up has no residual effect, and has no effect on seeds, so new weeds can begin to sprout immediately. While there are other things that can stop this, most are not recommended when you're going to be replanting your lawn.

I see this is an old post but new people may have these same questions and this past fall i did the same thing that g6342856 did.

I had a weedy area about 4000 sq feet on side of house that had agressive weeds and only a few small patches of healthy grass .So i first mowed to lowest possible setting then round up for a month like morpheuspa said.

Then water the dirt each week to see any areas you missed then repeat round up again. After a months time either level the area or rototill .If area is level just rough up the existing top soil and sow the seed.

Before you do this incorporate some starter fertilizer into the soil that prevents weeds and does not interfere with new seedlings. Then your good. I recently filmed a two month renovation i did in August and i used titan rx turf type tall fescue with good results and im now weed free you can see video below.

It took some hard work but well worth the wait

Yes, but don't rototill afterward. Tilling destroys the capillary structure of the soil created by roots and microbes over the years. If the soil is not level or profiled the way you want it, fix the surface by dragging a drag over it. Chances are you do not need more soil. The soil that's there can be improved.

Yes i agree i just had to because of my situation thats why i mentioned for him its better to use the soil thats there. My situation was uneven and lot of divets so i needed but , i agree only in rare cases to do it.

If there are holes, then use sand or topsoil to fill. Bringing in a load of soil will not improve the soil that's already there. But it will change your drainage and quite often for the worse.