How can I get rid of weeds but not kill my plants?

cover or tie back any nearby plants you don't want to kill, then spray the leaves of the weeds with the solution....good luck!!

You may have to smother them out with more newspapers and mulch. Even covering the other plants I would be afraid to use chemicals as it still gets into the soil just spraying the leaves.

pour boiling water over them

You can burn weeds with a blow torch but if the weeds invade the roots of your plants you'll have to dig and remove the invaders. At that point I would temporarily pot the plants (unless they are huge shrubs) and spray the weeds with Spectracide non-selective herbacide. Allow the weeds to flurish prior to this so there is above ground foliage to carry the herbacide to the roots, but before seeds set. A hot sunny day will improve it's efficacy. Allow time for the weeds to die and dry out the roots. Before putting the plants back I would enrich the planting holes with a weed free composted steer manure. Then add news papers or landscape fabric and more mulch. You have add more mulch periodically to keep weeds down and if seeds are being blown in or bird deposited there's a product called Preen that prevents germination.

product called weed and feed.

Never had much luck with Preen...is there a "trick"?

Preen is a seed-sprouter- preventer. It will not do a thing to actively growing weeds.