how to plant perennials

Here's my back hill renovation in progress.

Design tips

Besides the basic rules of "place sun-lovers in sun and shade-lovers in shade" and "don't plant one of everything", the key thing is to make sure you leave enough space between plants.  Sure, those perennials are small right now (especially if you buy the cheap ones, like me), but check the tag to see how big they are going to get and resist the urge to pack them in too tightly.  Plants that are too close together may lack air circulation and be more susceptible to diseases such as powdery mildew, not to mention the fact that in a couple years they'll be too big and you'll have to dig them all up again.  If you like the tightly packed look, throw some annuals in between to fill the spaces for a few years, otherwise add mulch to keep the weeds down.  In a few years when the plants are bigger, they'll cover the bare spots and keep the weeds down themselves.

Planting tips

Plant in the morning or evening or on a cloudy day, to reduce the stress on the plants.  Dig a hole twice the size of the plant's pot and throw a couple of handfuls of compost and one handful of bonemeal in the bottom of the hole.  There, you've just fertilized your plant for the first year at least.  If the plant is rootbound, loosen the roots before planting, then back fill with the soil.  Be sure to water plenty in the first few days after planting, and regularly for the first year until the plant is well-established.