Proper watering techniques and plastic mulch

I have a new perennial flower garden which was put in this year. Plastic is down with mulch over it. What is the best way to water so that the plants are receiving enough water. If I place a soaker hose, it just seems to run off. Thank you.

Doug says "plastic?" is down. You *don't* put plastic down over a garden and then cover it with mulch.

You don't put landscape fabric down in a perennial garden and then cover it with mulch. (Note that some gardeners put landscape fabric down in straight shrub beds) Perennials grow too fast and too large for landscape fabric and you wind up having to remove it or choke out your perennials.

So. Step 1 - this fall when the perennials are finished, pull up all the plastic layers you've put down. Replace the mulch around the plants,

Step 2. Drip irrigation will work fine then. Understand that the average drip hose will cover a width of approximately 3-4 feet (about 18-24 inches on either side of the hose) so that tells you how far apart to lay the hoses.

So sorry to have to tell you but you have to get rid of the plastic layer if you want a perennial garden there.