A Gallery Art Nouveau dahlia grows 12 to 24 inches tall and blooms from midsummer through frost. Dahlias come in 20,000 varieties. If your summer landscape needs a color infusion, next spring consider planting dahlias, a summer-flowering bulb that blooms from July through frost. With more than 20,000 listed varieties in 10 different categories, you can grow dahlias in every color but blue. And, with options up to 5 feet tall, dahlias can add both style and substance to your garden.
For the best results, dahlias require full sun and well-drained soil. To keep them blooming, fertilize plants monthly with a low nitrogen fertilizer and regularly "deadhead" their spent blossoms. Make sure plants are properly watered, especially if they are growing in containers, or if the weather is especially hot or windy.
Robin Carlson / Chicago Botanic Garden
Dahlias are native to Mexico and Central America, and are not winter hardy in the Midwest. Their tubers need to be lifted, dried, and stored in the fall.
••Groom your borders to improve plant appearance and maximize flower production. Gently remove dried or yellowed bulb foliage since the bulbs are going dormant and have already stored food for next year's flowers. Remove spent flowers (deadhead) on your annuals and perennials to encourage them to continue flowering. Remove yellow foliage to keep the plants neat and tidy.
••Prune water sprouts (vigorous shoots on the inside of the tree and on the trunk) and suckers (vigorous shoots growing from the base of the plant). Crab apples and hawthorns tend to send out lots of water sprouts and can benefit from this type of pruning.
••This is a good time to cut some of your outdoor flowers for indoor display. It is best to cut the flowers during a cool part of the day and to put them in water as quickly as possible. Remove any foliage that will be under the water in the vase. Adding a preservative to the water can lengthen the life of the flowers.
••Weeds growing between cracks in brickwork are unsightly but easy to eliminate. Treat them with a nonselective herbicide when they are small to avoid having to pull them out by hand.
••Installation of plant material can continue through the summer. Try to keep plants moist before planting to minimize stress on the new plant material. Containerized plants can sometimes be difficult to remoisten if they are planted dry. Be sure that they have been watered before planting. Newly installed plants need about 1 inch of water a week. Frequency of watering may need to be increased during periods of hot windy weather. Plants that were grown in containers need more frequent but light watering until their roots establish into the garden soil.
••Keep in mind these general rules when harvesting most vegetable crops. First, it is important to harvest vegetables when they are at the peak of their flavor. Younger plants and fruits are often more tender than those left on the plant longer. The length of time vegetables remain edible depends on weather conditions. High temperatures hasten maturity. It is also important to handle them carefully during harvest time. Check the garden daily and remove any ripe, damaged or misshapen fruits. Fruits that are not easily removed from the plant, such as eggplant, should be cut with a knife. Harvest regularly to encourage production. Many plants, such as cucumber, okra and zucchini, will cease production if mature fruits are not harvested.
••For a more natural appearance in your garden, prune according to each plant's growth habit and make your cuts at different heights. Cutting right above the leaves will help mask the cuts. View plants from all sides before pruning and periodically as you are pruning. Try not to leave any voids in the plant form by distributing cuts evenly across the plant. For a more formal appearance, make your cuts at the same level. If spreading disease is a concern, disinfect your tools with Lysol disinfectant or a solution of 9 parts water to 1 part bleach. Plants have hardened off for the season and in most garden conditions will regrow very little if at all.
Tim Johnson is director of horticulture at the Chicago Botanic Garden in Glencoe.
