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The trouble with roses 1

Double Pink Knock Out Rose. Photo courtesy Star Roses

Double Pink Knock Out Rose. Photo courtesy Star Roses

Questions about sick roses continue to fill my inbox and the aisles of  garden centers.

Many roses, including the tough-as-nails Knock Outs, did not rebound after our brutal winter. Several of those that did make it through don’t look great.

There’s some thinking that the roots of the plants were damaged by the severe season. They are no longer able to support adequately the top growth, rendering the plants weak and susceptible to insects and diseases.

Cutting the roses back hard – close to the ground – is what we did in spring, but if the plants still are not thriving, consider cutting back again. This reduces the top growth and allows the roots to heal and grow. Fertilizing isn’t necessary, but a good dose of compost around the base of the plant will help.

In the first of a two-parts, here are some common problems we’re seeing:

Rose slug damage on leaves. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Rose slug damage on leaves. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Rose slugs. These are the larvae of the rose sawfly. They are a pale green and are usually present in spring and as they dine, they give roses a stained-glass look.

Pear slugs. The damage from these larvae is similar to rose slugs, but appears in summer.

These insects can defoliate roses and give the plant a burned look. Be vigilant about inspecting the undersides of leaves. Remove any larvae or use a strong spray from a hose to knock them off.

Rose mosaic virus leaves tracks in the leaves, eventually turning they yellow from a lack of chlorosis. Photo courtesy Kansas State University Extension

Rose mosaic virus leaves tracks in the leaves, eventually turning them yellow from a lack of chlorophyll. Photo courtesy Kansas State University Extension

Rose mosaic. This virus can be spread by insects as they munch and move among the plants. We can spread it, too, with tools that are not cleaned with a 10 percent bleach solution after each use on a sick plant. The disease stunts the growth of roses and causes mottled leaves, which lose their green becoming chlorotic.

Once a rose is infected, you can remove affected branches, but the disease remains in the plant. Eventually, the rose will be weakened and likely will die. Consider removing and destroying affected plants to keep the disease from spreading to healthy roses.

Black spot is the most common disease on roses. Eventually, it can weaken and kill the plant. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Black spot is the most common disease on roses. Eventually, it can weaken and kill the plant. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Leaf spots. Roses can be affected by two different leaf spots: black spot and spot anthracnose. Black spot, which appear on the top of the leaf, is probably the most common disease on roses. Eventually, the leaves turn yellow and drop. This disease weakens the plant.

Anthracnose is an opportunistic disease that may show up in hot weather. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Anthracnose is an opportunistic disease that may show up in hot weather.
Photo courtesy Purdue Plant and Pest Diagnostic Lab

Anthracnose spots may show up in really hot weather. The spots are fuzzy. Leaves turn yellow and drop off.

Make sure that any pesticide you select is labeled for the problem you have.

Next week, we’ll look at a few other common rose problems.

Patriotic pop for pots

A pot of Lanai Red verbena, Whirlwind White fan flower, white lantana and Angleface Blue angelonia herald the patriotic hues of the Fourth of July. © Jo Ellen Meyers Sharp

A pot of Lanai Red verbena, Whirlwind White fan flower, white lantana and Angleface Blue angelonia herald the patriotic hues of the Fourth of July.
© Jo Ellen Meyers Sharp

If you are looking for a patriotic pop of blooms for the upcoming Fourth of July holiday, here are some suggestions.

First, go with premium annuals. These are usually in 4-inch (or larger) pots and cost considerably more than bedding plants. But premium annuals give you a lot of bang for your buck because they already have good size and maturity, making them showy right from the start.

Garden centers will stop selling bedding plants soon, if they haven’t already. Growers are no longer producing these because once they reach a certain size, it’s too hard to keep marigolds, petunias, vinca, salvia and other bedding plants alive in those tiny four- or six-pack plastic trays.

As the season progresses, even the premium annuals start to look a little scraggly. Because they are in larger pots, the plants can can be cut back, fertilized and allowed to rest for a couple of weeks before they start to rebloom, making them worthy of space on the garden centers’ tables and your deck or patio. Rehabbed plants will have a tighter growth habit, too, with more flowers. A premium annual costs $4.50 to $5 each.

Keep in mind the components of a container. Thriller is the focal point or dramatic plant. Fillers are mounded plants that take up space, usually at a mid-level in the pot. Spillers cascade over the side of the pot.

So, what would be good choices for your red, white and blue patriotic pot? Here are some suggestions of annuals for full to part sun locations.

Red

  • Tall red salvias (S. splendens) work well as a centerpiece in a container
  • Red geraniums serve as fillers and red petunias, verbenas are fillers and spillers.

White

  • Victoria White mealycup sage (Salvia farinacea) can be used as a centerpiece plant. These get 15 to 18 inches tall and bloom all summer.
  • White verbena, petunia, lantana, fan flower (Scaevola) all have mounded, trailing habits. Diamond Frost euphorbia fills the pot with tiny starts.

Blue

  • Royal Velvet Supertunia, which is probably the best selling petunia on the market. The deep purple-blue flowers didn’t lose their scent during the hybridizing process, either.
  • Victoria Blue mealycup sage adds nice height as a centerpiece in pots.
  • Angelface Blue angelonia looks like 18-inch tall stalks of orchids. Use as a centerpiece or thriller in a pot.

Cannas add tropical flair to the Midwest garden

‘Maui Sunset’ canna, under planted with ‘Kong’ coleus, strikes a dramatic pose in the garden. © Jo Ellen Meyers Sharp

‘Maui Sunset’ canna, under planted with ‘Kong’ coleus, strikes a dramatic pose in the garden.
© Jo Ellen Meyers Sharp

When I was a little girl, I’d trek down the alley to my great grandmother’s house a block away. Her side yard was a gardener’s bounty, with a circle of tall red cannas at the center. Whenever I see these stately plants, I think of her and her garden.

Although cannas (Canna) are an old-fashion flower, they provide a trendy, tropical feel to the garden, deck, patio, porch or balcony. Ranging in height from about 2 to 6 feet, they are as dramatic in the ground as they are in pots.

A canna is a rhizome, and can be found already growing in pots in garden centers this time of year. Or, rhizomes can be purchased at garden centers in early spring in a package or through online or mail order retailers. Pot these up in March to get the growing process started before transplanting outdoors in mid to late May.

Look for virus-free rhizomes and plants. For the last 10 years, cannas have been troubled by one of three viruses, spread, the experts say, by aphids. The virus can cause malformed leaves or flowers and create speckles or streaks in the foliage. When buying canna plants, make sure they are symptom free.

The fact that cannas have red, yellow, orange, pink, off-white or speckled flowers and that hummingbirds like the blooms is sort of a bonus. To many, the real beauty of the plant is the lush foliage. Depending on which cultivar you have, the leaves will be green, purple, golden or striped.

Cannas are tough plants and do best when planted in full sun, but are quite tolerant of shadier locations. They can take it wet or dry, but prefer soil that is well drained and evenly moist. Cannas also can be planted or grown in pots in the margin or edge of ponds or water gardens. The blue-green leafed cannas seem best suited for pond planting.

There’s nothing quite like a canna leaf striped with green, red, purple or yellow, backlit by the late afternoon sun. It just screams tropics. Flowers and leaves can be cut for indoor arrangements.

After the tops are killed by cold temperatures, remove the foliage, dig and dry the rhizome and store in a cool, dry place. Pot up next spring for another season of beauty.

Japanese aster a long-time bloomer

‘Blue Star’ Japanese aster sports light blue flowers throughout the summer. © Jo Ellen Meyers Sharp

‘Blue Star’ Japanese aster sports light blue flowers throughout the summer.
© Jo Ellen Meyers Sharp

Don’t you love it when you find a new plant to try?

That’s how I felt when I found the perennial ‘Blue Star’ Japanese aster (Kalimeris incisa) sitting and blooming by itself on a garden center table a couple of years ago, late in the season. Of course, I bought and planted it.

Last weekend, I found another ‘Blue Star’ Kalimeris sitting alone on a garden center bench. Yes, I bought it and plopped it right next to a ‘Blue Star’ that I planted two years.

Aster is a good description for the 1-inch wide flower with pale blue petals and yellow center. But unlike the sprawling, late-blooming asters (Symphyotrichum) we’re familiar with, this one stays upright and blooms pretty much all summer.

The Missouri Botanical Garden says this is a ‘tried and trouble-free’ plant in its landscapes, and I can second that opinion.

Grow ‘Blue Star’ in full sun or part shade. The leaves are thick, making it more tolerant of drought. This plant does fine in well-drained clay soil and Indiana’s hot, muggy summers. ‘Blue Star’ gets up to 18 inches tall, spreading to form a nice clump 18 inches wide. It blooms from June into September. (Plant native asters, too, for monarchs and other critters looking for nourishment late in the season.)

Rose troubles continue

If your roses weren’t killed by snow-mageddon, they may be under attack from rose slugs, aphids and spider mites.

Spider mites make yellowish or orange dots on the leaves. The veins of the leaves are green, but the tissue in between is chlorotic – pale green or yellow. Rose slugs munch holes in the leaves and sometimes completely defoliate the plant. Roses will likely releaf once the insect is brought under control. Aphids, too, suck on plants, causing malformed buds, leaves or stems.

The best defense can be found at the end of the hose. A strong spray of water can knock of many aphids, mites and other insects, reducing or eliminating the need for insecticides or miticides. Other controls include:

  • Snip off any damaged buds or leaves.
  • Remove spent blooms to reduce hiding places for thrips, which are commonly called rose slugs. Removing spent blooms also reduces the hiding places for Japanese beetles. These beetles prefer plants in the rose family, which includes fruit trees and many ornamental trees and shrubs.
  • Neem oil, summer horticultural oil and spinosad are environmentally friendly products that control for insects. Always read and follow the label directions.