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Originally published Thursday, June 5, 2014 at 6:15 AM

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Avoid problems with diseased impatiens; smart watering

Garden writer Ciscoe Morris on a new strain of the fungus disease that is attacking impatiens, and on the importance of watering in our dry summers.


Special to The Seattle Times

Gardening Events

Ciscoe’s Picks

The Secret Gardens of Lake Forest Park 12th Annual Garden Tour & Garden Fair-Plant Sale: 9 a.m.-4 p.m. June 14 (tour begins at 10 a.m.). Tour of five gardens, featuring artists and musicians. The Garden Fair-Plant Sale is at the Town Center at Lake Forest Park, 17171 Bothell Way N.E. Ciscoe Morris will broadcast his radio show live from the fair (10 a.m.-noon). The fair is free, the tour costs $12 in advance or $15 day of (www.secretgardensoflakeforestpark.com).

Grand Opening of the New Visitor Center and the Trillium Store at the Bellevue Botanical Garden: Begins at 10 a.m. June 14, with events throughout the day. “Music at the Garden” to celebrate Father’s Day on Sunday, June 15. 12001 Main St., Bellevue; free (www.bellevuebotanical.org).

Father’s Day Weekend at Chase Garden: 10 a.m.-3 p.m. June 13-15. 16015 264th St. E., Orting; $5, free for fathers (www.chasegarden.org).

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In the Garden

If you’ve been looking for the common garden impatiens this year (Impatiens walleriana) with no luck, it’s because they’ve become susceptible to a mysterious new strain of the fungus disease called “Downy mildew.” Many nurseries have stopped carrying them.

The first clues of trouble are reduced flowering and premature leaf drop, but you’ll know something is amiss when the plants wilt and fall over. A look at the undersides of the leaves will reveal the white down that earned this disease its name. Downy mildew is spread by spores that blow in the wind and can infect plants both nearby as well as those miles away. Since impatiens have been such a mainstay in home and commercial gardens, the disease quickly spread throughout the Pacific Northwest. To add insult to injury, once your impatiens get the disease in your garden, long lived, highly infectious spores survive in the soil, making it practically impossible to replant impatiens again for the next eight to 10 years.

You still can find garden impatiens at a few garden centers, and in theory the disease can be prevented by using fungicidal sprays, but it’s harder than it sounds. Sprays must be applied before infection occurs, and at regular intervals all summer long. In addition, this disease rapidly develops resistance to fungicides, so it’s necessary to alternate products used.

A better solution might be to try some different shade-loving bedding plants. New Guinea Impatiens is highly resistant to the disease and has showy blossoms that come in a wide variety of lively colors. Tuberous begonias have big, tropical-looking flowers in all sorts of hot colors, and wishbone flower (Torenia fournieri) features brightly colored snapdragonlike blooms that are highly attractive to hummingbirds.

Don’t forget to water

Proper watering is the key to a beautiful garden in the Pacific Northwest. Despite our reputation for rain in the Puget Sound region, it’s feast or famine when it comes to precipitation. The vast majority of our 36 inches of rainfall occurs in the winter months, while in most summers we suffer drought conditions.

From the start of May until the end of September we average less than 7 inches of liquid sunshine. Compare that to the approximately 20 inches of precipitation that falls during the same period in Wischeescin (where I grew up), and it’s apparent why it’s necessary to water adequately to keep most plants healthy and attractive.

This is especially important for newly planted trees, shrubs and perennials. New plantings need to be watered as often as necessary to keep the soil evenly moist for at least a few weeks to give plants time to grow a sufficiently deep root system to fend for themselves. Once plants are well established, however, it’s better to water them deeply and infrequently. Remember that soil dries from the surface down.

Light, frequent watering doesn’t tend to penetrate deeply and keeps only the surface moist, which encourages shallow, less drought-tolerant rooting. Deep, infrequent watering, applied slowly from a soaker or drip system, on the other hand, penetrates much deeper into the soil, fostering deeper rooting and increased ability to withstand drought.

Mulching the soil surface can also help reduce the need to water as often because it keeps the soil cooler, decreasing evaporation. It’s a lot of work to mulch the garden, but I suspect you’ll think it was worth it when you see the cost savings on your water bill.

Ciscoe Morris: ciscoe@ciscoe.com. “Gardening With Ciscoe” airs at 10 a.m. Saturdays on KING 5.



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