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Late Summer Care for Flower Gardens

gardening by Mary Robson, WSU Extension Agent
Intense sun and blue skies illuminate annual and perennial gardens during late summer. Hot weather challenges gardeners to keep flower gardens looking fresh and tidy. This is the season of delphiniums gone to seed, lilies dying back, and daisies finished blooming. What can be done to care for bloomed-out plants and polish up the garden for fall enjoyment?
   Start by exploring display gardens and nurseries for perennials that bloom now and into fall. Adding a few new plants can enliven a tired garden quickly. Sunny garden areas invite the addition of asters, which bloom in white, rose, and lavender, but are most known for clear, autumnal blues. A good performer is Aster frikartii "Monch," violet-blue yellow-centered, which blooms from July through September.
   Asters range from about 6 inches tall to 4 feet, depending on the variety. Be sure they have excellent sun and good drainage; they die out in soggy soils. Two excellent older cultivars are "Marie Ballard," with double powder-blue flowers, and "Patricia Ballard," with double rosy pink blooms. Asters also prefer watering weekly before and during bloom.
   Is the garden shaded? Shady fall flower gardens are brightened by Japanese anemone, one of the most elegant of the late-blooming perennials. The most common carries tall, crisp, white, open cupped flowers with intriguing soft green centers. Another Japanese anemone often seen in gardens has single pink flowers. Both the white and pink varieties grow to about 4 feet tall in rich soil. They do require moderate watering, but can handle considerable drought.
   For sunny areas, consider rosy Sedum "Autumn Joy" salvias such as Salvia azurea and Boltonia asteroides, which has five foot branches of soft white daisy-like flowers. Boltonia's small flowers look good staked up at the back of a sunny garden; it can become a floppy tangle if not tied up.

Tips for a tidy garden
   Tidy the garden by cutting back spent foliage on delphiniums and early day lilies. Dead-head annuals and trim off spent flowers from dahlias and gladiolus. Dahlias need regular water and fertilizer throughout their blooming period, until darker colder weather shuts them down.
   Trim Shasta daisies that have finished bloom. Mid-August is a good time to lift, divide, and replant German iris.
   Carefully pry clumps out of the ground, and pull them apart. Trim off any dead portions. German iris grow from one end of the rhizome, gradually dying out at the other end. Some iris growers, particularly if the plants have had soft rot problems, dip the trimmed portions into a solution of household bleach, 1 part bleach to 10 parts water. Then allow the iris to dry off in the sun for a few hours, or longer, before replanting. Plant in a sunny, well-dug soil.
   Do not cut off any foliage of true lilies until the stems are completely brown. Lilies must replenish the bulbs for next year's bloom and shouldn't be cut back when still green.
   If you're planting now, enrich the soil with compost or composted manure. Perennial borders need good soil preparation, so take the opportunity to dig deeply and add soil amendments whenever the garden's being worked. Fall-planted perennials do not need fertilization when planted, but can benefit from compost dug into the area. If there's no home-grown compost available, use any one of several commercially available composts.

Get rid of weeds now
   Weed well before mulching; in late summer many annoying weeds set seed and set their plans to fill your garden with thousands of their descendants. If the garden has been invaded by perennial weeds such as morning glory, dandelion, or blackberry, grub them out now.
   Morning glory can be spot-treated with gluyphosate (sold as Round-Up or Kleen-up, and under other names). Pull it out now and allow the plant to regrow a bit (don't worry, it will!), then spot treat the re-growth. Glyphosate is a non-selective weed killer that will kill any green plant it touches, so be very careful using it around valuable plants. Painting the leaves with the substance using a sponge paintbrush works well. Wear gloves, goggles and long sleeves when handling any pesticide and follow label instructions.
   Annual weeds, common in all gardens, can be chopped out and controlled with applications of mulch. Their seeds aren't able to germinate when buried in 2 to 3 inches of mulch. When mulching the perennial garden, keep the mulch back away from the crowns of plants, the growing centers to prevent disease.

Plan ahead for spring blooming bulbs
   While August days are here, think about where to plant fall-planted bulbs, and which ones to choose. Strange as it is to contemplate daffodils or tulips now, October is planting month and bulbs appear in nurseries just around Labor Day. Best supplies are generally available early. If you purchase spring-blooming bulbs, store them in cool location until planting time. Transfer them to paper sacks for storage; the plastic sacks tend to hold moisture and may rot the bulbs or cause a green mold to appear.
   Tulips and narcissus bulbs, and indeed all spring bloomers, are harmed by high temperatures. Do not leave them in the trunk of the car after purchase on a hot day. Treat these bulbs as you would a sack of groceries, carefully.
   Mulching, weeding, trimming, and adding plants--late summer is a busy time in the flower garden. And watch out, fall will be even busier!

Visit WSU's Agriculture Site on the World-Wide Web at http://www.cahe.wsu.edu.