Coneflowers and rudbeckia go together like vanilla and chocolate.

Salvia, Russian sage and asters are cheerful fall cohorts. Clematis entangled with roses on a tower offers twice the beauty.

You get the idea. Pairing plants is a bit like being a matchmaker. Successful marriages require common ground - site, soil and light conditions. But there's no explaining attraction - foliage, colors and combinations. Ultimately your garden should make you happy, whether or not it follows "the rules."

Love is blind

When garden centers open in spring, come-hither foliage and coquettish blooms make it hard to resist running through the aisles, breathlessly choosing this one and that one … then throwing your arms wide and shouting, "I'll take them all!" We've all been there, done that, and regretted most of those impulse purchases. There's that sinking feeling when you realize you fell for pretty faces, you bought more plants than you've got space for and everything will be done blooming by early summer.

Play with combinations at the garden center. Load your cart, find a corner and take a hard look. Do the colors look good together? Is the foliage attractive? Depending on size at maturity, how many plants will you need for clumping or drifts? What are the bloom times?

It takes two

Try one of these basic techniques and see which fits you best. Nothing is foolproof, so pay attention to details.

Balance and unity. Shades of the same color create a unified appearance, but are the colors, foliage and sizes too similar? Gertrude Jekyll cautioned against "clinging" to themes to the point of distraction, and you may unwittingly be developing a theme. If all the plants are similar, the garden will be a yawner.

Keep an eye out for Mother Nature's own combos. Find a color wheel for inspiration in your color schemes.

Play up contrasting leaf colors and shapes. Foliage lasts long after perennial flowers, in particular, are spent. On the other hand, if there's too much contrast, the visual result is chaotic. Repeat your color/foliage choices but don't alternate colors in a predictable pattern - it looks too obvious. Contrasting warm and cool colors also can be pleasing. Separate conflicting colors with silver- or gray-foliaged plants.

Experts recommend starting a plan with fall- and winter-interest plants, then add summer and spring bloomers. Consider combinations for each season. Include something bold and dramatic.

Gardens have layers

Ogres like "Shrek" have layers; gardens have layers, too.

Many perennial gardeners recommend double-digging garden beds because it improves productivity, porosity and drainage. No sugar-coating: It's hard work; ask me, I've done it.

Before digging, call Iowa One Call at (800) 292-8989 to have someone mark your utility lines.

The most sensible double-digging directions are from Organic Gardening magazine: Begin at one end of the bed and dig a 1-foot wide and 1-foot deep trench across the bed's width, placing excavated dirt in a wheelbarrow. Next, work a garden fork into the floor of the trench and slowly rock it back and forth to loosen the soil. Continue until the soil in the excavated area is loosened. Dig a second, similar-size trench next to the first, this time placing the excavated soil in the first trench. Loosen the soil at the bottom of the second trench with the garden fork. Dig another trench and backfill the second trench, loosen the bottom of the third trench, and continue this process until you reach the end of the bed. Fill the last trench with the soil excavated from the first.

Another tip: Add a shovel of peat and a shovel of compost for every three shovels of original garden soil to loosen and enrich soil.

After you've recovered (and seen a chiropractor), dig in, installing any small trees, evergreens and shrubs. Then plant herbaceous perennials, ornamental grasses, etc. Dig in tulips, daffodils and lilies to proper depth around the perennials. Tuck in shallowly planted bulbs and corms (muscari, alliums). Fill in any bare spots with annuals.

General rules of thumb: Arrange plants with the tallest in the rear, shortest in the front. Then break the rules by moving some taller plants forward and shorter plants back for visual interest.

Water, then add mulch to reduce weeding, conserve moisture and make the garden look finished.