I'm trying to picture this (and I'm probably not doing too well ;\ )

'Rocks on the beds' - I'm thinking fist-size or a bit larger. If I was asked to move them I'd either do a dark of night trip to the local river bank and liberate them - or use them under any new concrete being laid or use them in a drainage sump. If the garden design made it appropriate I might also use them to construct retaining walls with or without mortar.

If the rocks are more the size of thumbnails then I'd keep them aside as useful hard mulch.

The plastic I'd dispose of. Yes, plants will do their best to grow with that on the surface but it does cut a lot of moisture from the roots and sets plants up for insect troubles, fungi, and interesting diseases.

Once I'd cleared it away I'd feed the soil with compost as generously as I could afford. If I was guarding the pennies then I'd eke it out by using at least a couple of gallons to any hole I dug for new shrubs going in. Mixed with the soil from the hole, because I wouldn't want the plants to get too accustomed to luxurious living!

The weeds: I'd want to know whether they were annuals or perennials. If they are annuals - the sooner they are out of the ground and onto the compost heap the better - preferably before they've had time to set seed. If you restrict any watering to just the plants you want to see flourish then the annuals will have to wait for the next rainfall. Once those little green sprouts show - off with their heads - using a good sharp hoe or hand cultivator. Whichever tool suits you for hand weeding.

Perennials: it's usually worth the effort to take them out completely by digging them up and burning them, if this is allowed in your area, or putting them out with the garbage when they're dry. (Lighter for the garbage folk...) And, if they've been yard residents for a few years - expect to be doing this for a few years to come. It does improve - unless any neighbouring yards are weed havens. If that's the case you need to do frequent garden 'patrols' and remove any plant pests as soon as you see them.

Good places to look are under favourite bird trees, or where the wind dies away in your yard (for plants that arrive on the breeze such as thistles and ragweed and dandelions...)

EWWW!!. Seems more than a few "non gardeners" use rock mulch....awful isn't it....but at least you have something under them. If you can pull up that plastic and get rid of as much of the rocks as you can....your gardens will be a lot happier. Rake the rocks out of the garden onto a tarp and haul them away.
Then put down a nice organic mulch and listen to your plants give a sigh of releaf....pun intended!
Linda C

I agree with Linda, clean out those rock beds and pull up the plastic before doing any planting. After cleaning out the beds then add some nice organic material. In my gardens we just toss anything, veggie scraps, egg shells, tea bags, coffee grounds and grass clippings. You might want to add some manure too if needed. If the rocks are good sized ones you could use them to boarder the plantings if not find a place that needs better drainage and liberate those rocks.

Stacie

Some plants like rocks. I've several succulents growing in a pile of football sized rocks with a sandy soil in the cracks. We live in a rather harsh desert environment and there is a purple flowering thing called ''Perovskia" that rather prefers gravel and just grown down through the plastic beneath. There are reports of seven different ''Perovskia". Perhaps some will grow in your climate.

Agree with everyone else, get those rocks and the plastic nonsense out of the beds.

It's a drag to pick up rock, I know, but really -- if you tried covering them and planting over them, you'd just curse yourself every time you wanted to plant something new. And it's exponentially more difficult to weed in rocks too.

Basically, re-read what vetivert8 posted; that's great advice!