Question
Sijka,
    Could you please give me some general pointers on how to prepare a part of a grassy lawn to be a perennial bed?
    Thank you!
    Sincerely,
    Lil

Answer
First though you MUST prepare your soil. It may be pains-taking but you will see such better results from your garden, sun or shade.

You didn't say where you live but this is my formula and I have good topsoil for about 5-6"" but then a lot of clay.

For every 6' x 6'sq. area:
1 bag peat moss (If you get the very large 3.cu.ft bags-only 1/2)
1 bag sand-play sand
1 bag gypsum (this helps to aerate the soil-you'll want to add some each year-but only 1/4th the amount, it will work it's way into the soil.
1/3 bad Millorganite (an organic fertilizer found at
Nurseries--and I SWEAR by it for flower beds and lawns, for lawns, put it on heavy like any fertilizer
in spring and fall!)
1 bag cedar or dypress mulch-this gets tilled into the
soil with all the other stuff.
3-4 bags Manure.  I buy mine in bulk-I like horse or chicken the best.  Elephant manure is said to be the VERY best-but I don't like big pets!

Roto-til or turn into soil with shovel-at least 8"-10" in depth-more if possible, before planting. You will be AMAZED!!


Then and only then are you ready to plant.
Sijka