For many of us the most enjoyable part of designing a perennial flower garden is choosing the specific assortment of both small and large perennials. You come to this, of course, only after factoring in the soil, light, and climatic conditions of the area you've chosen for a garden. Several factors come into play at the same time as you make your choices. Color and bloom season are two. Form, texture, and spread are also important.

Designing with Large Perennials

Cooler colors at the back of your garden--the three-foot blue Caesar's Brother iris, for example, or the seven-foot climbing Clematis Jackman--tend to make a space appear larger. Warmer colors--red daylilies, for example, or Oriental poppies--appear closer and are good for dramatic displays. Remember as you combine colors that the warm ones often overwhelm the cool.

If the back of your garden is partially shaded by ornamental or shade trees, you might want to consider the Astilbe fanal for one of your large perennials. This is a deep red feathery flower. A lovely butter-cream colored flower tolerant of partial to full sun, the Mary Todd daylily reaches just over two feet and is adaptable across soils.

Whatever color and form you choose for your large perennials, remember to factor in their lateral spread. You want the ground in the back of the garden amply covered but not a jungle of leggy plants. As you choose flowers toward the front, you'll step them down incrementally in height, the middle groupings anywhere from 18 inches to perhaps 12 inches. Your border plants will be usually about six inches high.