Outdoors blossom during May

In May, home landscapes are fully alive.

A symphony of green leaves reinvigorates the landscape, and spring-flowering trees, shrubs, perennials, and annuals reward gardeners with colorful flowers to enjoy both indoors and out.

It's a time that rewards past hard work and motivates new and exciting additions that will add beauty for years to come.

May is also good time to revisit the importance of proactive and preventive care. Healthy plants are better able to avoid problems with disease or insects. And when problems occur -- and even the best gardens have them -- usually the earlier they are detected the easier they are to solve.

Here are things you can do this month to get the growing season off to a healthy start.

Garden care

• Plant warm-season annuals, vines, herbs and vegetables after the Chicago area's average last frost date of May 15.ˆ½ Cautious gardeners often wait until Memorial Day before setting out cold-sensitive plants such as tomatoes, peppers, eggplants and squash.

• Continue to plant perennials, ornamental grasses and roses in containers.ˆ½ If plants are root-bound, make four cuts into the bottom of the root ball with a sharp tool, and flare the sections outward when planting.

• Monitor all container plantings for dry soil.ˆ½ On warm, windy days, hanging baskets will require water every day. Terra-cotta pots will dry out faster than plastic. Consider incorporating the recommended amount of water-absorbent products into container soil.

• Provide a gentle water drip for migrating birds.ˆ½ Birds that migrate in May (warblers, tanagers, orioles and buntings) are attracted to shallow pools and the pinging sound of dripping water.

Flowers

• Stake tall perennials before they reach 6 inches.

• To promote stocky growth, pinch back fall-blooming perennials such as chrysanthemums, asters and tall sedums once a week until the middle of July.

• Continue to direct the growth of perennial vines on their supports.

• Continue to check peonies for botrytis blight or other fungal problems.ˆ½ Peonies affected by botrytis or bud blast last year should be sprayed regularly this year, starting when the plants are 2 to 4 inches tall. Cage or provide support for peony blossoms when the plants are 10 inches tall.

• Let spring bulb foliage yellow before removing it.ˆ½ The leaves use sunlight to manufacture food that is stored in the bulbs to fuel next year's growth.ˆ½ Braiding daffodil leaves can reduce the number of flowers.

• Spray emerging lily shoots with anti-rodent spray if rabbits have been a problem.ˆ½ Reapply after rainfall.

• Plant summer- and fall-flowering bulbs such as dahlias, peacock orchids (Acidanthera), cannas, tuberous begonias, freesia, gladioli, montbretia, and calla lilies.

Trees and shrubs

• Trees and shrubs can still be planted this month.ˆ½ Plant on a cloudy day, early in the morning, to prevent heat and transplant shock.ˆ½ Water thoroughly and gently at planting time and throughout the first year with 1 inch of water a week.ˆ½ Mulch root zones to conserve moisture.

• Prune spring-flowering shrubs and ornamental trees immediately after they bloom.ˆ½ These include forsythia, viburnum, lilac, small magnolias, rhododendron and azalea. Prune to the ground old canes of forsythia and lilac.

• Fertilize roses with a liquid 20-20-20 solution when flower buds are set.

• Monitor roses for insects and disease.ˆ½ Check daily for black spot, especially in wet weather. Make sure leaves are dry before removing infected leaves and spraying with an approved fungicide.

Lawns

• Mow lawn to 2 to 2½ inches, removing one-third or less of the leaf blades.ˆ½ Leave grass clippings on the lawn to return nutrients to the soil, or add them to a compost pile.

• If you are applying grass seed, do not use a pre-emergent weed killer in the same area.

• If necessary, fertilize lawn in mid-May. Late fall is a preferable time to fertilize.

• Monitor for weeds and hand pull or spot treat accordingly.ˆ½

Fruits, vegetables

• Plant corn, snap beans, and summer squash in mid-May.

• Thin carrots, beets and late lettuce.

• Harvest green onions, lettuce and radishes.

• Harvest mature asparagus and rhubarb.

Houseplants

• Begin to harden off warm-season transplants, moving them into a cold frame or protected area.

• Gradually move houseplants outside to protected areas. Large houseplants in plastic pots should be slipped into heavier pots to prevent them from tipping over in wind.ˆ½ Guard against overexposure to afternoon sun.

• Overwintered tender annuals or tropicals (hibiscus, gardenia, geranium) may be pruned, fertilized and taken outside once night temperatures are 40 degrees.

• Denise Corkery is a horticultural writer for the Chicago Botanic Garden.