Here's the scoop on popular annuals and perennials
If you're thinking of planting perennials, be sure to look for Zone 4 or lower hardiness, i.e. plants that survive average minimum temperatures of -20 to -30 degrees – that's our climate.
Most perennials hardy in Zone 4 need some winter protection – primarily mulching; most need quite a bit of sun. There are many varieties of perennials, each with many needs, including temperature conditions, planting requirements, resistance or susceptibility to disease or insect invasions, bloom time, feeding requirements and so forth. Not that these are particularly difficult or picky; once you get most of these perennials in the ground, they'll do just fine.
Catalogs from nurseries that offer perennial plants are good study guides, although you may want to look up the same plant in several catalogs to compare data; some catalogs – especially those from nurseries in fairly temperate zones – don't zone plants appropriately. Yes, a Zone 5 plant (able to survive average minimum temperatures of -10 to -20 degrees) might survive Minnesota winters if planted in protected areas and are well-mulched each winter. But you could lose the plant in a very cold winter.
For a permanent reference, get a book on perennials (available for $8 to $100) or the perennial plant booklet published by the Minnesota Landscape and Nursery Association from many nurseries for 50 cents and $1. Use these to learn about plants and to help you plan your garden.
Try to establish a plan that gives you lighter-colored plants in shady areas, perennial blooms all season (possibly by interplanting groups of early-, mid- and late-blooming flowers), plants of appropriate heights (taller one in back, for instance) and mixed foliage textures (such as the large leaf of a tall canna lily near a stand of baby's breath). Choose single color schemes (all whites, or a purple-red combination) or combinations that please you (even orange and pink if you like).
Keep in mind that you'll want to see your plants both from close up (as you walk by, as you weed, as you sit on your garden bench), and from afar (through your dining room window, as you drive up to the garage, or from the deck). Plan focal points – a tree, a statute or bird bath, a fence or an arbor – that draw attention, around which to coordinate your plants.
Take into consideration taller, distant objects as well. You may enjoy that glimpse of the top of the IDS building peeking out between trees, but despise the bumblebee-painted side of the town's water tower. Take advantage of the first, and plant a tree or build a tall structure to screen the second. Perennials
Asters Hardy asters are among the longest-blooming and showiest in the garden, although they don't usually start blooming until late summer and fall. The individual daisy-like blooms are nice for cut flowers, and also supply masses of color as other garden blooms are fading or gone.
Astilbe This plant does well in shade and is a great textural plant in the garden, with tall, fluffy flower wands in colors ranging from white through pale to bright pinks to a rich magenta, and fine ferny foliage that sometimes has a touch of bronze. Combines well with hosta. Heights range from 12 to 36 inches.
Baby's breath (Gypsophila) Any gardener who likes to cut bouquets, fresh or dried, or who likes the look of a lacy cloud in the garden would enjoy growing this easy-care plant. There are single- and double-flower forms, white and pink varieties. There are short (6-inch) to tall (40-inch) varieties.
Chrysanthemums Here's a war-horse in the autumn garden, but be sure to look for varieties that are hardy to Zone 4. Many have been developed by the University of Minnesota; those often have "minn" in their names. The painted and Shasta daisies are forms of chrysanthemums that bloom in summer. Many potted chrysanthemums should be treated as annuals.
Clematis This vine has dozens, maybe hundreds of cultivars, many of which are hardy in our climate. The most obvious is the Jackmanii, with rich, lush purple flowers, but there are varieties in many forms and colors ranging from white to magenta, striped pinks and blue. Flowers can be up to 6 inches wide, and the seed pods are lovely after the blooms are spent. They look nice on a fence, trellis and even growing among the foliage of a climbing rose.
Coneflowers (Echinacea) This native prairie flower, usually purple but also available in white, is a yeoman of the garden. Hardy, reliable, attracts butterflies, nice cut flower. You don't even have to deadhead - leave the stalks in all winter to attract birds to their seeds.
Coralbells (Heuchera) Here's a nice, hardy plant, with ground-hugging (ground-cover) leaves in variegated greens to bronzy-purple with tall wands of delicate blooms in pinks, whites and reds. And it does well just about anywhere - even light shade.
Coreopsis A nice, easy plant that brings a sunny yellow to the garden and cut bouquets. It's available and hardy in several forms, from a mum-like button form to a daisy form (there is one daisy form that's available in pink). It blooms more if you deadhead spent blooms.
Daylilies (Hemerocallis) This is one of the easiest perennials to grow: They take sun or some shade, need little maintenance and thrive under even unfavorable conditions. They also come in hundreds of colors from yellows and oranges to reds, pinks and bi-colors; plus tall, short, medium, ruffled, double or twisted. Delphiniums Ah, the blue spikes of the delphinium - such a charming, elegant flower. Some people call it "challenging" to grow, and it isn't always hardy in Zone 4, but keep on trying, just mulch it well in winter. Several varieties range from 3 feet to occasionally 8 feet tall. There are several blue shades, plus white and pink.
Dianthus Also known as pinks, or tiny carnations, these hardy spring flowers bloom most of the season if spent flowers are cut off. The spicily fragrant plant has flower colors ranging from rose and pink to sharp reds, whites, salmon and yellow. Foliage colors in silvery blue or green add contrast to the garden. Heights range from 6 to 24 inches.