Spider mites like it hot. Watch your roses

QUESTION: What could be stripping the leaves off the branches of my roses? I spray with a product that is supposed to protect roses from insects and diseases, but it hasn’t helped.

Keep an eye on roses when it’s hot and dry. Spider mites can turn a lovely rosebush into an ugly mess.

This time of year, with this kind of weather, suspect spider mites, which thrive when the weather is hot and dry, say rosarians at the Nashville Rose Society. The tiny creatures get on the undersides of leaves and feed on the plant’s juices. The damaged leaves look speckled, turn yellow and fall off.

Spider mites are not insects; they are more closely related to spiders, so insecticides won’t have any effect. You can use a miticide, but it can be expensive. The best and cheapest way to control them is with a blast of water directed at the undersides of the leaves, rosarians say. If you do this every three days for a week or so, you break the mites’ gestation cycle.

Here’s a little more information about the tiny arachnids: Adult mites are less than 1/50 inch long. They use their mouthparts to pierce individual plant cells and remove the liquid. They produce webs that can coat the foliage with a fine silk that collects dust, making the leaves look dirty.

You can’t see them, but you can certainly see the damage. Heavily infested plants will be discolored, and if they are not controlled, the rose can be stunted, or even killed.

Record heat is trouble for trees

Meteorologist Bobby Boyd sends me email from time to time about extreme weather conditions. The latest concerns the large dome of high pressure building eastward out of the plains and across the Tennessee Valley that has put Middle Tennessee, as he says, “in the pressure cooker.” We’re breaking records this weekend. No rain in sight, and gardens are suffering.

Young trees and shrubs are especially vulnerable. The Nashville Tree Foundation has sent an alert with watering guidelines and new tips that you can read here to help trees survive.

Keep these tips handy. It’s still only June, and we’ve got a long way to go.

Coming up in July

July 14:  Middle Tennessee Iris Society rhizome sale, 8 a.m. – 3 p.m. at Ellington Agricultural Center. All types of irises available in a variety of colors, priced from $1 – $6. A great chance to add to your collection! To learn more: For additional information see our web site www.middletnirisociety.org.

July 17: Middle Tennessee Orchid Society meets at 7 p.m at Cheekwood. On the agenda: an orchid auction and discussion on Cattleya Orchids. To learn more, visit www.tnorchid.com.

July 17: Perennial Plant Society meets at Cheekwood in Botanic Hall. Refreshments and plant swap at6:30; meeting and program at 7. Guest is Kelly Norris, horticulturist, plant breeder and manager of Rainbow Iris Farm inBedford,Iowa will present “The Modern Plant Explorer.” The meeting is open to the public.

July 26: Farmer Jason performs at Family Night Out at Cheekwood, 6:30 p.m. The event is free with regular Cheekwood admission. www.cheekwood.org.

July garden calendar

Does this heat make you wish for a shade garden? Find tips on plants that have it made in the shade, plus things to keep you busy in the garden in July, in Saturday’s Landscape & Garden calendar in The Tennessean.

Best time to tame a rose

Question: When is the best time to prune roses? I have a bush that needs trimming, but don’t want to damage it by pruning at the wrong time.

If the rose is out of control, it won’t hurt to get out the clippers now. This advice comes from Annie Owen, a Master Rosarian and member of the Nashville Rose Society: “If the bush is overgrown, this is an okay time to prune it back, as long as it gets plenty of water.” In fact, if you reduce the size of the bush, you reduce its need for water, she said.

This goes for most types of roses, even those with finicky personalities and special fertilizing and spraying needs, as long as they’re healthy. If it’s a Knockout rose, no worries at all. “If it’s a Knockout, you can’t kill those things,” Owen said.

The Nashville Rose Society offers these pruning guidelines: Use sharp bypass pruning shears, which will make a clean cut without crushing the stem. Start by taking out older wood, along with any dead or dying canes. Remove any canes that rub or cross each other, or any twiggy, unnecessary growth. Make each pruning cut about ¼-inch above an outward-facing bud eye, where the leaf is attached to the stem.

Rose enthusiasts who winterize their prized roses will do more severe pruning in the fall. To begin the winterizing process, stop fertilizing roses now to allow the plant to slow down production of new growth. Early in October, stop cutting the dead flowers and leave the rose hips in place. In late November or early in December, cut the canes back to 2 to 3 feet, and place a mound of mulch around
the bush. This will hold them until spring, when you should prune lightly again to get new growth.

For general good advice on pruning and anything else that has to do with roses, visit the Nashville Rose Society’s Web site, www.nashvillerosesociety.com.

Meeting: The Nashville African Violet Club meets at 1:45  p.m. at the Green Hill Women’s Center, 10905  Lebanon Road in Mt.  Juliet. To learn more about this organization or specifics on this meeting, contact Julie at Julie.mavity@gmail.com or call 615-364-8459.

Calendar: It’s August, and time to start thinking about fall – specifically, about what to plant in a fall garden. Find suggestions in the August Landscape & Garden Calendar in today’s Tennessean and at Tennessean.com.

It’s too hot to garden, but all is not lost over at Turning Toward the Sun.

The trouble with roses

The leaves on my climbing roses developed little black spots and now all the foliage has dropped off. What is this?

For questions on roses, I always go to the helpful experts at the Nashville Rose Society, and their Web site. It looks like there are at least two fungal diseases that cause black spots on the leaves of roses: one appropriately called black spot, and the other, anthracnose. You can tell the difference by looking at the edges of the spots. Black spot has the feathery margins, which give rise to some of its other names: leaf blotch or star sooty mold.

Both make a rose look really bad for awhile, which is why people who are serious about growing fancy, beautiful roses stick to such a rigid schedule of spraying. Fungicides are to ward off the ugly fungal diseases, pesticides to keep away chewing and sucking bugs.

Both blackspot and anthracnose overwinter on the plant and develop in the incubator of a cool, most spring. Cleaning up around rose bushes (getting rid of dead leaves and decaying matter), pruning out affected canes, giving the rose bushes plenty of air and reducing the amount of time water stays on the leaves can go a long way toward reducing the development of disease spores. Fungicides, applied on a regular schedule in early spring, can help prevent infection.

The problem of dealing with and preventing rose diseases is one reason landscapers and gardeners plant so many of the ‘Knock Out’ varieties, which bloom all summer and are resistant to most of the ugly diseases that plague garden roses.

Which leads to another question a friend asked not long ago:

Are ‘Knock Out’ roses real roses?

I understand the reason for the question, because it does seem impossible, doesn’t it? Given all that you hear about how you have to prune, spray and coddle rose bushes to get them to look their best, how can there be these easy-care upstarts, this ‘Knock Out’ series that seems poised to take over the rose universe? To get a rose expert’s view on the topic, I talked to Anne Owen, a Nashville Rose Society consulting rosarian.

 “They are, in fact, a really true rose, in the genus Rosa,” she said. “The fact that they don’t require spraying for fungal diseases puts them in a category with very few others.”

Most rose enthusiasts, she said, like the challenge of growing the big, show-stopping roses – the ones in striking colors and with exceptional fragrance. And those are the ones that require coddling. “If you want a great big cabbage rose or a big hybrid tea, you’re going to have to spray.”

But a ‘Knock Out’ finds a place even in the most serious rose gardens.

“I think most rosarians have a ‘Knock Out’ or two because they are such great plants,” Owen said.

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This month in the garden: Welcome the blooms, not the bugs: June Landscape & Garden Calendar in The Tennessean.