Peonies may suffer in wet weather

QUESTION: Some years our peonies bloom beautifully for several weeks, but sometimes the buds die before they open, or black spots develop on some of the plants and the leaves curl and die. Can you tell me what I’m doing wrong?

Peonies may develop botrytis, a fungal blight, in cool, wet weather.

Sometimes it’s not anything you’re doing wrong. You may be able to blame the peony’s problem on the weather. Wet, cool weather provides perfect conditions for a fungal disease called botrytis, or gray mold.
Extension agents note that botrytis flourishes on a lot of plants this time of year if there is not enough sunshine and a lot of wet weather. There is a specific fungus, Botrytis paeoniae, that infects only peonies.
The blight can infect the young shoots as they emerge early in spring, and can infect buds or flowers at any stage. On plants that are in bud, the buds may swell but will die before they open. The infection can move into the stem and cause spots and discoloration. If the infection is severe, the leaves will turn brown and die back prematurely.
Good garden practices can help keep Botrytis from damaging the peonies. Inspect the plants and remove any parts covered in gray mold; place them in a bag to be discarded (don’t put them in the compost). Do this on a day when the weather is dry to avoid spreading the fungus. In the fall, clean up dead foliage and debris, cut the peony stalks at ground level and discard the debris to reduce the chance of the fungus spores returning the following spring.

May Garden  Calendar

May is planting time in Middle Tennessee. Food or flowers? Why not both? See the May Landscape & Garden Calendar in The  Tennessean for five ornamental and edible plants for your landscape.
Garden events in Middle Tennessee
May 4
Carmen Johnston, a Garden Lifestyle Expert for Southern Living Plant Collection, will host a session on spring-inspired ideas using the Southern Living Plant Collection Designer Series container gardens. The event starts at 10:30 a.m. at Home Depot on Moore’s Lane in Brentwood.
May 10
National Public Gardens Day at Cheekwood, celebrating public gardens and Cheekwood’s role in promoting environmental stewardship, plant conservation and community education. Live music in the Herb Garden 10 a.m. – 2 p.m.; guided garden tours on the hour. Special presentation with Cheekwood president Jane Offenbach at 1 p.m. Learn how to receive free admission at http://www.nationalpublicgardensday.org. More info at http://www.cheekwood.org.
May 11: Spring Festival & Plant Sale presented by the Wilson County Master Gardener Association. Guest speakers, demonstrations, food and concessions, gift baskets, crafts, gifts; flower garden and arboretum tours by tram. 9 a.m. – 4 p.m. at the James E. Ward Agricultural Center at Wilson County Fairgrounds in Lebanon, Tenn. Free admission and free parking.
May 11
Middle Tennessee Hosta Society sale, dozens of hosta varieties available. Sale opens at 8 a.m. at the Maryland Farms YMCA in Brentwood.
May 11
Robertson County Master Gardeners plant sale, 8 a.m. – 1 p.m. (rain or shine), County Extension Plaza, 408 North Main St. (corner of North Main & 5th Ave.), Springfield, Tenn. For information: http://www.rcmga.org.
May 11: Wilson County Master Gardeners Spring Festival & Plant Sale, 9 a.m. – 4 p.m. at the James E. Ward Agricultural Center, Wilson County Fairgrounds in Lebanon, Tenn. Speakers, demonstrations, food and concessions, crafts, gifts; garden and arboretum tram tours. Free admission and parking. http://wcmastergardener.org.
May 21: Perennial Plant Society of Middle Tennessee meets at Cheekwood’s Botanic Hall. Speaker is Jimmy Williams from Paris, Tenn, on “The Perennial Border from February through December.” Refreshments at 6:30, meeting at 7 p.m.
May 23: Middle Tennessee Hosta Society meets at Cheekwood’s Potter Room, 7 p.m. Featured speaker is Jason Rives, owner of Petals From the Past in Jemison. Ala.; topic is “Incorporating Antique Roses into the Hosta garden.”

Powdery problems

I have three peonies. Two are fine, but the third, in a different location, is completely covered with powdery mildew. How does that happen? Should I do something about the one that’s covered? Or just leave it and hope for the best?

Powdery mildew (which affects all kinds of plants in the landscape) can be a problem when weather conditions are right and cultural conditions are less than perfect. It’s a fungus that thrives in warm weather when the humidity is high. It becomes more of a problem for plants that are growing in damp, shady places and overcrowded conditions.

It’s a common disease and you’ll know when it hits: look for patches of gray-white, powder-like growth. It usually appears on the tops of leaves but can also be seen on the bottoms of leaves, and on young stems, buds and flowers. It likes the young, succulent parts of plants.

At the UT Extension Soil, Plant and Pest Center, expert Alan Windham (who frequently provides answers to questions here) says the peony should survive with no problem. It’s a good idea to remove any dead or dying foliage and destroy it (don’t put it in the compost; that probably won’t kill the fungus spores), and clean up around the area.

Windham is more worried about downy mildew in beds of impatiens, which we mentioned in this column several weeks ago. “There are lots of cases coming in from all over the state; it’s been found in nearly every state east of the Mississippi,” he says.

Watch for plants that are losing leaves, that don’t flower, and that have white growth on the undersides of the leaves, he advises. The disease can be extremely damaging, so pull up, bag and dispose of infected plants to keep it from spreading.

Bad news this year, but even bigger implications for next year regarding availability, use by commercial landscapers and their general viability as a bedding plant, he said. Does that mean the ubiquitous impatiens won’t be among the gardener’s favorite go-to shade annual next year?

“Begonias, SunPatiens and New Guinea impatiens are going to be in high demand,” he says.

If you haven’t seen the Soil, Pest and Plant Center’s Facebook page, check it out here. “We’re putting lots of good stuff up,” Windham says.

Garden events in MiddleTennessee

Sept. 5:WarnerParkNatureCenter hosts Hummingbird Happy Hour, 4 – 6 p.m. at the WarnerParkNatureCenter. Bird banding demonstrations and other kid-friendly activities are on the agenda. Free admission, but registration is required; call 352-6299. While you’re there, visit the NatureCenter’s vegetable, herb and flower garden. Info: http://www.nashville.gov/parks/nature/wpnc.

Sept. 15: Urban Chicken Appreciation Day at Shelby Bottoms Nature Center, 10 – 11 a.m., celebrates feathered backyard friends. Learn how to get started in backyard chicken keeping in a session led by Bonnie Bowles. Call (862-8539) or email (shelbybottomsnature@nashville.gov) to register.

Sept. 22 & 23: Many rare and unusual houseplants will be available at the Tennessee Gesneriad Society’s annual Flower Show and plant sale, which will be held at Cheekwood’s Botanic Hall. The event is open to the public 9:30 a.m. – 4:30 p.m. Saturday, and 11 a.m. – 4:30 p.m. Sunday. To learn more contact Julie Mavity-Hudson at Julie.mavity@gmail.com.

Sept. 29: Herb Society of Nashville’s Herb Day at Cheekwood’s Botanic Hall: “Cooking & Gardening with Native Plants.” 9 a.m. – 4 p.m.; admission is $40 plus Cheekwood gate fee. To register: www.herbsocietynashville.org.

Evergreens turning ever-brown

QUESTION: We are seeing many evergreen trees — Leyland cypress and others — with big sections of brown limbs. Is that due to the drought? Or is there some other problem affecting the trees?

The drought this summer plays a big part in the browning of Leyland cypress, but it’s not the whole story. Alan Windham, at UT Extension’s Soil, Pest and Plant Center says the branch dieback is the result of a one-two punch: drought and seirdium canker, a fungus that appears on branches or stems and in branch axils and causes the branch to die. “I’ve seen more damage this month than I can remember in several years,” Windham says.

I found a good description of seirdium canker at the Web site of North Carolina State University’s Plant Pathology Extension: The cankers are brown or purple sunken patches on the bark, and may be accompanied by a flow of resin. Affected branches may be scattered randomly throughout the tree; they turn a reddish-brown color, in striking contrast to the green, healthy foliage. The fungus can be spread by splashes of rainwater or water from sprinklers, or it can travel from branch to branch on unclean pruning tools.

There are no chemicals recommended to control the canker. Brown branches should be pruned and destroyed as soon as possible. Prune at least an inch below the canker, and sterilize the pruning tools between cuts by dipping them in rubbing alcohol or a solution of 1 part chlorine bleach to 9 parts water. Plants that are severely affected should be removed and destroyed. Watering by drip irrigation during drought can help prevent problems, Windham says.

Upright arborvitae are also having trouble due to the drought. Windham explains: Plants have different strategies to survive: some plants sacrifice older leaves to protect new shoots; some have waxy leaves, some plants roll their leaves or close up to prevent water vapor from escaping.

“Then you have plants like arborvitae, where it’s all or nothing. It’s as if the plant is saying, ‘We’re going for broke. Everything survives or nothing survives.’ Well, this strategy didn’t work out too well for many arborvitae I have seen.”

In this case, the only solution is to remove the dead trees and start again.

Garden events in Middle Tennessee

Aug. 21: Two meetings at Cheekwood’s Botanic Hall:

- The Perennial Plant Society meets at 6:30, beginning with refreshments and plant swap. Program begins at 7 p.m., and the speaker is Audubon naturalist Sherra Owens, presenting “Gardenening On The Wild Side With Nature’s Most Important Plant.”

- The Orchid Society of Middle Tennessee meets at 7 p.m. Michael Wenzel of the AtlanticBotanical Garden will speak on Phalaenopsis species.

Both meetings are open to the public.

Aug. 23: The Middle Tennessee Hosta Society meets at Cheekwood, 6:30 p.m., in the Potter Room. Guest speaker is landscape designer, photographer and writer Troy Marden; his topic: In a Southern Garden: Lessons from 20 Years of Gardening in the South.” To learn more about MTHS, visit www.mths-hosta.com.

Next month in Middle Tennessee

Sept. 5:WarnerParkNatureCenter hosts Hummingbird Happy Hour, 4 – 6 p.m. at the WarnerParkNatureCenter. Bird banding demonstrations and other kid-friendly activities are on the agenda. Free admission, but registration is required; call 352-6299. While you’re there, visit the NatureCenter’s vegetable, herb and flower garden. Info: http://www.nashville.gov/parks/nature/wpnc.

Sept. 15: Urban Chicken Appreciation Day at Shelby Bottoms Nature Center, 10 – 11 a.m., celebrates feathered backyard friends. Learn how to get started in backyard chicken keeping in a session led by Bonnie Bowles. Call (862-8539) or email (shelbybottomsnature@nashville.gov) to register.

Sept. 22 & 23: Many rare and unusual houseplants will be available at the Tennessee Gesneriad Society’s annual Flower Show and plant sale, which will be held at Cheekwood’s Botanic Hall. The event is open to the public 9:30 a.m. – 4:30 p.m. Saturday, and 11 a.m. – 4:30 p.m. Sunday. To learn more contact Julie Mavity-Hudson at Julie.mavity@gmail.com.

Sept. 29: Herb Society of Nashville’s Herb Day at Cheekwood’s Botanic Hall: “Cooking & Gardening with Native Plants.” 9 a.m. – 4 p.m.; admission is $40 plus Cheekwood gate fee. To register: www.herbsocietynashville.org.

Prevent powdery mildew

QUESTION: How do I keep my beautiful zinnias from getting powdery mildew? It may be too late for this year, but what should I do different next year?

Powdery mildew is a fungus that thrives when nights are moderately cool and foliage stays damp. It travels by airborne spores, and appears as gray or white splotches on leaves, stems and flowers of susceptible plants, such as zinnias. A mild case is merely unattractive; a severe case of powdery mildew can cause distorted shoots and leaves, misshapen flowers or can prevent flowering altogether.

The best defense is to give zinnias room to grow without crowding, which allows air to circulate better around the plants, and water only in the morning, so the foliage has time to dry before nightfall. Cut back on the use of high-nitrogen fertilizer, which produces succulent new growth that is a major powdery mildew magnet. Grow them in full sun; hot temperatures (above 90 degrees) inhibit the growth of mildew.

There are fungicides available that should be applied as soon as you begin to spot the mildew (so yes, probably too late for this year), but I always suggest trying the good-cultural-practices method first. The University of Tennessee Extension has a short list in a publication about powdery mildew here. If you decide to go that route, be sure to read and follow directions on the product label.

Zinnias are not the only things plagued by powdery mildew. Lilacs, roses, crepe myrtles and other woody ornamentals, and many herbaceous ornamentals and bedding plants are also targets when weather conditions favor the fungus.

Coming up

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 at 6:30; meeting and program at 7. Guest is Kelly Norris, horticulturist, plant breeder and manager of Rainbow Iris Farm in Bedford, 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.

Suffering from a summer brown-out

QUESTION: Why is my fescue grass turning  brown? I water 2 to 3 times a week and have it professionally treated  (fertilized and weed control). The lawn company says that’s just the nature of  cool weather grass in the summer heat. What do you think? — Charlie

A cool-season lawn may suffer in summer.

I’m not a lawn expert, but I do a lot of research to answer readers’ questions. Here’s what I’ve found:

It is the nature of fescue, which is a cool-season grass, to turn brown in the summer during hot weather, especially during dry periods. It goes dormant, and will green up again when the weather gets cooler.

However, there is also a fungal disease called “brown patch” that may affect fescue lawns. The symptoms include small brown patches that get bigger. It might start with a ring of brown grass with a patch of green in the middle. Individual blades of grass will be brown, but the plant will be green at soil level. If this symptom isn’t present, it may just be the summer heat. It’s a good idea to know for sure what the problem is before applying unnecessary fungicides.

Lawns do well with about an inch of water a week. They don’t need to be watered every day, but water deeply maybe once a week if it doesn’t rain. (Too much water may do as much harm as too little). It’s also a good idea to cut the grass higher. If it’s cut too short, it leaves the lawn vulnerable to more weeds and diseases.

I found this garden expert’s web site that may offer a little more information:
http://www.walterreeves.com/lawn-care/fescue-diseases.

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How much are garden-grown stringbeans worth? Plenty, if you have to protect them from marauding rabbits. See my solution over the garden journal, Turning Toward the Sun.

Tomato troubles

I have two questions for The Garden Bench:

1. The tomatoes on one of my tomato plants keep turning flat and black on the bottom before they get anywhere near ripe.  Any idea why that is and what to do about it?
2. When is the best time to dig up the garlic I planted last fall? — Anne-Marie Farmer

Soil with sufficient calcium produces prettier tomatoes, without blossom end rot.

The tomato question is a timely one, Anne-Marie, because it’s July, when most gardeners who grow things to eat think about tomatoes. In the July garden calendar in today’s Tennessean, there are several tomato tips. But to answer your questions here:

1. The tomatoes have a condition called blossom-end rot. It’s fairly common, and is due to a calcium deficiency in the soil. Try adding a bit of pelleted garden lime. It may not help immediately, but it will add calcium to the soil that will be available to plants in the future. You can also work crushed eggshells into the soil.

Recently I read the suggestion to put about 3 cups of whole milk (not 2%, not skim) into a hose sprayer and use it to spray the soil around the plants. Try not to get milk on the leaves, and rinse it off with plain water if you do.

2. Dig up the garlic after the leaves have started to turn yellow. Let the bulbs dry in the sun for a few hours, then lay them out on screens where they can cure for a couple of weeks. After they are cured, brush off as much soil as you can, but don’t wash them. You can braid the bulbs together and hang them to dry, or dry them in mesh bags. If any are damaged, use them as soon as you can. 

 Coming up next week: Middle Tennessee Iris Society’s iris rhizome sale is next Saturday (July 9),8 a.m. – 3:30 p.m., in the Ed Jones Auditorium atEllingtonAgriculturalCenter. Middle Tennessee Iris Society VP Dan Kula says there will be a big selection of varieties and colors, priced from $1 to $6. Admission to the sale is free.

What’s happening this month? See the July Landscape & Garden Calendar in today’s Tennessean.

 Early-spring planting, early-summer harvest: Click over to A Garden Journal to see what we pulled out of the ground.