I would first cut the plants down with the mower. Then, if you live in an area with lots of fall leaves, I'd mulch with leaves. lots of 'em. I usully put at least a two foot thick layer of whole fallen leaves first to smother the grass and weeds, then add another two foot layer of leaves I have run over with my mower a couple of times to chop them up and make them stay put a little longer in the wind - chopping also makes then look a little neater. If it is breezy wet the leaves after you spread them to keep them in place. If you add enough leaves - and it will take a lot - you can smother anything. The leaves will decompose and be a great soil additive by next summer. You might want to repeat the treatment next fall if there are woody plants or really tough grasses you're trying to get rid of. There is no such thing as adding too many leaves as long as you are willing to wait for them to break down. If you get impatient it is not hard to rake off some of the leaves after they have done their job of smothering the plants.

I would definitely not add any "erosion control" fabric or weed control cloth or anything like that. In my experience those things eventually get weeds growing through them - often the weeds start above and send roots down through the fabric - and them they become a nightmare to remove. No such problem with fall leaves.

I find adding a layer of newspaper underneath to be unnecessary and not as easy as it sounds - I usually end up with gaps between the paper. Also, too much newspaper can break down slowly and be a pain when you try to turn the bed in a year or two.

An erosion control blanket is not for killing vegetation but for helping to establish vegetation and to minimize the forces of erosion that naturally occur on a slope. Weed blocking fabric is used to deprive light to a given area.
If you use an erosion control blanket (as opposed to weed blocking fabric) you start with bare soil, put seed on the soil and then cover with the blanket to prevent the seed from being washed away and help it establish. That is what I did to establish grass on a steep slope. Another option with the blanket is to put it on the slope after you have killed the existing vegetation and cut slits through which you plant your plants. I suppose you could also use a blanket just to hold your mulch in place but burlap or something else would be cheaper than a true erosion control blanket.

I wonder what exactly is growing there now and how dense is it... I hate to remove vegetation on a slope. Depending upon what is growing there and how dense it is - I might consider mowing the existing vegetation real short and then overseeding/slit seeding wildlfowers right into the existing vegetation. I would keep the overseeded area mowed short for a few years and then let it grow...

Wildflowers tend to grow differently when they have some grasses and stuff to compete with. I think if you overseeded with them and slowly worked on weed control - it might fill in nicely. (Though this depends upon what is growing there now and how dense it is...)

I probably would not smother in this situation. I think getting mulch and smother materials to stay on a slope might be problematic. I might use the multiple applications of round up scenario, because then the dead vegetation could stay in place and help hold the soil on the slope until the new seedlings started growing.

And erosion control blanket is a good idea - if you kill off the existing vegetation. Though the blanket probably wouldn't be needed if you can do an overseed scenario.

My related question is about my southern New Hampshire home. The lawns here are huge and time-consuming to mow, so I am investigating converting two large areas to lower-maintenance plantings. I could irrigate both areas, but prefer to do it only for one year if at all.

Area A: A triangular, north-facing slope in the front of the house, all grass, moderately steep but still currently mowed, full sun, bounded by paving and by low-growing evergreen shrubs. Piled up snow from the driveway melts late.

Area B: Fairly level on the side of the house, bounded by sunken edging, woods, and a grass field. Very lush grass, low traffic, part of it covers septic.

What do the experts recommend for plantings in A and B?

How to prevent erosion on the steeper slope (A) if I rototill it and then plant with wildflower seed? One option is a wildflower meadow, another is a groundcover that would cover well. If the solution involved mulch, I'd be concerned about it washing down the slope.

If I plant wildflowers in area B, how do I prevent them from encroaching on the grass (or vice versa)?

Thanks,
Laura

Wildflowers encroaching on turf grass is usually not a major problem if at all. Grass encroaching on the flower area is a problem and is dealt with by many methods including edging, trenching, RoundUp and hand pulling.

Rototilling a slope will increase erosion. See above comments for more ideas on how to handle slopes.