Yard & Garden Line News
Volume 6 Number 13                                                               August 15, 2004
Features this issue:

Late Summer Bloomers
This and Thatch=Patch Disease!
Horntails
Another Strange Summer in Minnesota
Apples -- Early and Tasty
Mark Seeley's Weather Notes:
August Garden Tips
Editorial Notes


Late Summer Bloomers
Nancy Rose, Regional Extension Educator, Horticulture

Tiger swallowtail on coneflower.
Rudbeckia trilobum Photo credits:
Beth Jarvis
Like a gardener tapped by too many mosquitoes, a flower garden can start looking limp and colorless in late summer. That spring burst of colorful bulbs is ancient history, and the early summer rush of fresh-flowered peonies, iris, and delphiniums is long gone. The cooler days of fall will bring classic autumn-bloomers like chrysanthemums and asters, but what can perk up the garden through the dog days of late summer?

Plenty. Lots of great perennial flowers come into their own in the heat of August, and others can be encouraged to extend their bloom with a little timely pruning. And perennials don't have to stand alone - annuals and even a few flowering shrubs also bring color to the late summer garden.

Native perennials, especially many prairie species, provide a rich source of late summer bloom. Coneflowers - a common name that's used for several different plant groups - could fill a garden on their own. One of the best known is orange coneflower (aka black-eyed Susan, Rudbeckia fulgida), including the popular cultivar 'Goldsturm'. Orange coneflower can slow down a bit by late summer, especially if not deadheaded, but the lesser known sweet black-eyed Susan (Rudbeckia subtomentosa) starts blooming later and is at its peak in the heat of August and early September. Another overlooked beauty is three-lobed coneflower (Rudbeckia triloba), a bushy biennial or short-lived perennial that is covered with bite-sized blossoms from mid-summer til frost. And if you want tall, try the towering (6-8 feet), lemon-yellow-flowered Autumn Sun coneflower (Rudbeckia nitida 'Herbstsonne').

Other coneflowers include the durable, heat loving yellow coneflower (Ratibida pinnata), and the ever popular purple coneflower (Echinacea purpurea). Purple coneflower's spiky orange-brown centers and drooping purple-pink petals make it a winner in gardens and in cut flower bouquets. This showy native also acts as an amazing butterfly magnet in late summer.Hot, sunny planting sites come to mind for late summer flowers like the coneflowers, but there are also some splendid late bloomers for moist, shaded sites. In August, moisture-loving cardinal flower (Lobelia cardinalis) sends up tall spikes of brilliant red, hummingbird-attracting flowers. Great blue lobelia (Lobelia siphilitica) also loves moist soils and produces many stalks of rich blue flowers from late summer to early fall. False dragonhead (Physostegia virginiana) thrives in moist soil and partial shade, but it also does well in drier, sunnier conditions. The creeping rhizomes of this fuchsia-pink flowered perennial will spread far and wide if allowed; try the more restrained, white-flowered 'Miss Manners' if you have limited space.

Yellow flowers predominate among late summer bloomers like coneflowers, sunflowers, and goldenrods. For a gorgeous contrast, combine those sunny toned perennials with blue and purple flowers. One of the best for late summer blues is Russian sage (Perovskia atriplicifolia), a tall growing semi-woody perennial with masses of tiny lavender-blue flowers from mid-summer on. Plant Russian sage in groups of three or more to produce an airy cloud of blue -- beautiful as a backdrop for other flowers.

Platycodon grandiflorus
Verbena bonariensis, flowering tobacco and hibiscus. Photos:
Beth Jarvis
Blues and purples are also found in the late summer flowers of balloon flower (Platycodon grandiflorus), ironweed (Vernonia sp.), blazingstar (Liatris sp.), and anise hyssop (Agastache foeniculum). And Joe-pye weed (Eupatorium maculatum), a terrific tall perennial for the back of the border, sports plate-sized clusters of tufted pinkish purple flowers in August and September.

Another winner in the big flower category is hardy hibiscus (Hibiscus sp., Zone 4 with winter mulch), with huge, tropical-looking flowers nearly a foot in diameter on 3-5 ft. tall plants. Many new and improved cultivars of this July to September bloomer have come into the market in recent years. Look for pink flowered 'Fantasia' and 'Sweet Caroline', red flowered 'Fireball', and the stunning 'Kopper King', which has rich copper-purple foliage along with bicolored white/pink flowers.

Additional late season color can come from annual flowers. Annuals make great filler plants in perennial gardens through the summer, but they're especially valuable now. Chunky annuals like geraniums and marigolds can look a little stiff in perennial beds; instead, opt for airy or spiky annuals that can intermingle with the perennials. Great choices for late summer color include mealycup sage (aka blue salivia, Salvia farinacea), Texas sage (Salvia coccinea), flowering tobacco (Nicotiana), and tall verbena (Verbena bonariensis).

And don't forget flowering shrubs when you're looking for some late summer pizzazz. The few shrubs that do bloom late in the season can be quite showy on their own or when mixed right into the garden. The large, cone-shaped flower clusters of panicled hydrangeas (Hydrangea paniculata) open white in late summer, then fade to pink and tan in fall. This large shrub can anchor the back of a garden bed along with tall perennials like 'Lemon Queen' sunflower and hardy hibiscus. For moist, shaded sites, the aptly named summersweet (Clethra alnifolia) is a gem. In late summer this small to medium sized shrub produces short spikes of sweetly fragrant pink or white flowers, perfect for mixing with cardinal flower and great blue lobelia.

Potentillas (Potentilla fruticosa) and some shrub roses (Rosa sp.) bloom all summer long, often right up until frost. Both also blend beautifully with late summer perennials and annuals. Potentillas bloom in yellow, white, or pink; deadhead old flowers to keep the plant looking fresh. Some shrub roses produce lovely flowers all summer, while others tend to bloom heavily in early summer, then send out a fresh flush of flowers in late summer and early fall. And the bright red-orange hips produced by some shrub roses add extra color as well.

If your garden is looking listless these days, consider adding some late bloomers to brighten up the lazy days of late summer. Check out your neighbors' yards, visit public gardens, and prowl the garden centers to get ideas for your own garden. Late summer to early fall is a great time for planting many perennials and shrubs, so you can even get a start on improving next summer's garden today.

This and Thatch= Patch Disease!
Janna Beckerman, Extension Plant Pathologist

Thatch. Photo Credit: Chad Behrendt
Excessive thatch commonly develops in highly maintained lawns, particularly newly (3-6 year old) sodded ones. Thatch is the layer of organic matter that develops between the grass blades, roots, and the soil. Thatch consists of living and dead grass stems, roots, and crowns-and the microorganisms that break it down. However, this decomposition occurs slowly. With increased fertilization, and increased growth of the lawn grass, thatch occurs more quickly than the microbes can decompose it. When the thatch layer exceeds ½", problems begin to develop.

An overdeveloped thatch layer blocks the movement of water, nutrients, and even air flow to grass roots. Roots become unable to establish, resulting in a shallow-rooted lawn that is predisposed to drought, and weather extremes. These conditions stress the lawn and favor the pathogens that cause disease.

Thick thatch layers predispose lawns to patch diseases. Symptoms of these many diseases look relatively similar, and are NOT diagnostic. These symptoms include circular, dead spots or rings of dead grass with live grass in the center, commonly referred to as frog's eyes. Typical patch disease symptoms include leaf color change from healthy green to tan-brown with the leaves often exhibiting a reddish color as they die.

Twenty years ago, a common term for "patch" problems was Fusarium Blight. However, the terms Necrotic Ring Spot (Leptosphaeria korrae), Yellow Patch (Rhizoctonia cerealis) and Summer Patch (Magnaporthe poae), are the appropriate names when discussing these problems. All of these diseases require laboratory examination for conclusive diagnosis.

Necrotic Ring Spot. Photo Credit: Plant Disease Clinic
These diseases attack grass roots and crowns, causing rot. Ironically, the very thick and lush lawn most people desire contributes to the spread of these fungi. These pathogens easily grow along and in the root systems moving from plant to plant and into the crown. Wet periods followed by warm dry conditions can "suddenly" bring on severe symptoms and the infected plants die during the slightest dry periods because they have no root systems to support them.

Preventing thatch prevents patch disease.
These diseases, once established, are difficult to manage. Although most homeowners don't realize it, the disease "has simmered" for three to four years before the symptoms developed. For this reason, the key to managing thatch-related patch diseases is prevention. In Minnesota, especially parts on heavy clay soils, preventing this problem is essential!

Soil compaction is a predisposing condition to both thatch and patch disease. Compacted soils delay or prevent roots from becoming established. Turf is weakened as a result of soil water logging and increased thatch buildup. Layering, the process where a few inches of topsoil are placed over, but not incorporated into compacted soil, results in a similar phenomenon, and prevent the sound establishment of roots. These problems are readily identified by the ease in which the sod is removed from the soil-it is easily peeled off because the roots have failed to establish.

To reduce thatch and encourage proper root growth, vertical mowers, or core-aerating machines can be rented, or lawn care companies can perform the work. Spring and late summer are good times for mechanical thatch reduction. Care must be taken in the timing of these treatments: Aeration and vertical mowing can damage existing grass. For severely compacted lawns, aeration may be required two or more times in a single season. On heavy soils, such as clay or clay loams, regular aeration is necessary to prevent soils from becoming compacted. Now is the time to begin planning, as the end of August and beginning of September are ideal times to de-thatch and core aerate.

Summer Patch Photo Credit: Jon Powell
Excess use of nitrogen fertilizer causes grass to grow faster than microorganisms can decompose the thatch. For this reason, avoid excess nitrogen, especially those people trying to reduce patch disease incidence.

Summer moisture stress is the trigger of summer patch development. To minimize patch development, proper watering once a week to a depth of 6 inches encourages deep rooting and healthy grass. However, if you are already have patch disease, water lightly and frequently to keep the top 1/2 to 2 inches of soil moist and minimize symptoms development. As the lawn begins to recover, gradually lengthen the time between waterings and apply more water each time until back to a normal watering program. This approach encourages root growth, while minimizing dieback.

For many people, patch disease appears to be the problem. The real problem, however, is poorly laid sod, soil compaction, or poor lawn care practices that lead to thatch development. For this reason, the emphasis should be placed on proper care to prevent disease establishment.

Please check out the new diagnostics web pages at
http://www.extension.umn.edu/projects/yardandgarden/diagnostics/


Horntails
Jeffrey Hahn, Assist. Extension Entomologist

Horntail. Photo credit: Jeff Hahn
The order Hymenoptera is divided into two groups. The first group contains some of our most familiar insects, the bees, wasps, ants, and parasitic wasps. It is known by entomologists as the suborder Apocrita. The second group, know as the Symphyta, are the sawflies and wood wasps. This group numbers far fewer species and its members are usually less recognizable. Unlike the bees, wasps, and ants which vary in habits, the Symphyta are all plant feeders. Many of the larvae in this group are caterpillar-like.

Within the Symphyta, one of the largest-sized and most conspicuous groups of insects are the horntails (family Siricidae). They are stout-bodied insects, measuring from one to two inches long. They get their name from a horn-like plate on the tip of their abdomen. On males it is relatively short while it is longer and somewhat spear-like in females. Females also possess a conspicuous ovipositor.

Horntails lay eggs in deciduous and coniferous trees that are either dead or in a greatly weakened condition. The eggs hatch into whitish, legless, cylindrically-shaped, worm-like larvae. They bore into the trunk and large branches, creating meandering tunnels in the sapwood and heartwood. Larvae eventually pupate in these galleries and emerge as adults, chewing a hole through the wood to escape. Because they rarely attack healthy trees, horntails are not considered a pest in the landscape.

The most common horntail is the pigeon tremex, Tremex columba. It is also the largest horntail in Minnesota, with females measuring two inches long. The pigeon tremex has a reddish brown head, a reddish brown and black thorax, and a black abdomen with yellowish stripes. It also has long, amber-colored wings. This horntail prefers maple but also commonly attacks many other deciduous trees, including oak, elm, hickory, apple, and birch. Adults are most active during August and September.

You might encounter horntails if have you a dead or a severely declining deciduous tree in your yard or a nearby area. Because they are not attacking healthy trees, no treatment is needed. Horntails may also be brought indoors in infested firewood or wood used in construction. Fortunately, they do not infest any wood found indoors and would die on their own in a few days. Despite their size and the ominous looking oviposter, horntails do not sting and are harmless to people. No control is necessary for horntails found indoors except for physical removal.

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm


Another Strange Summer in Minnesota
Deborah Brown, Extension Horticulturist

Fabulous tomatoes? They'll be late, if they ripen at all. Photo Credit: Deb Brown
Here we are in the middle of August, and – lucky us – we've already had a healthy sample of October weather. Sure, it's getting warmer again, but our vegetable gardens are paying the price for Mother Nature's capricious behavior. And so am I. I've been swamped with calls from TV and radio (and even a couple from newspaper reporters) – all asking how far our gardens are behind, and what can we do about it.

I'm not really sure of the first answer, but the second is easy: Not a darn thing.

Whether gardens are in trouble depends on which veggies are being grown. For the majority of folks it's tomatoes that are causing the most consternation. Even people who grow mostly flowers usually have a few tomato plants – none of them ripening fruit the way we expect them to this time of year.

All winter long we eat those cardboard grocery store tomatoes, but come mid-July our teeth are set for the real thing. And by mid-August, we're getting downright surly about not having them.

It's not just the tomatoes that are slow this year. All the heat-lovers – peppers, eggplants, sweet corn, melons, pumpkins, winter squash, okra (does anyone really like okra?) – are lagging behind. Of course, plants that prefer cooler temperatures are doing just fine, thank you. And so are most of our flowers.

In fact, many flower gardens are truly spectacular this summer. Cooler temperatures have resulted in more brilliant colors and extended the bloom time for many perennials. So at least we can grace our dining tables with lovely bouquets of flowers – even if we can't put out a plate of sliced home-grown tomatoes!

Apples -- Early and Tasty
Deborah Brown, Extension Horticulturist

Zestar.
Photo Credit: Deb Brown
State Fair time is when Minnesotans feast on a whole host of special treats that we don't usually indulge in the rest of the year. Mini doughnuts, deep fried Snickers bars, honey-sunflower ice cream, and foot-long hotdogs are just the tip of the iceberg. And, you can get those first local apples, fresh from the orchard!

Even though most early apples don't quite measure up to the flavor and keeping quality of many later varieties, they are still a treat, enjoyable partly because they're associated with the beginning of autumn and the changing of the seasons. For several years now we've also had Zestar!, the University of Minnesota's new early apple that's exceptionally tasty and stores quite well.

In addition to Zestar! Here are a few others to look for. These apples typically mature between mid-August and mid-September. They may be a week or so late this year.

* State Fair Unlike many early apples, State Fair is both crisp and juicy; great for fresh eating. These round, glossy red apples typically ripen at fair time and can be stored through the end of September.

* Hazen Ripening a few days later than State Fair, Hazen is good for cooking and baking as well as eating fresh. It's flesh is firm, juicy, and mildly flavored.

* Wealthy This very old variety, developed by Minnesota pioneer fruit breeder Peter Gideon, has long been a favorite cooking apple. It's also good eaten fresh. The apple is medium in size with red striped skin and a small core.

* Chestnut Crab Chestnut crabs are crisp and juicy, with a lively balance between sweet and tart flavor. Though mostly eaten fresh, they can be made into sauce or sliced and pickled for use as a condiment with meat. Averaging about two inches in diameter, these large crabapples are the perfect size for snacking.

If you grow your own early apples, be sure to pick them as soon soon as they ripen. If you leave them on the tree longer they begin to get softer and mealier and won't keep as well. Color, alone is usually not a good indicator of apple ripeness. Here's how to tell if your fruit is ready to pick.

* Apples should come off the tree easily.

* Seeds inside the fruit should be dark brown.

* They should taste ripe, not "green" or "starchy." Some mildly-flavored apples don't taste sour when they're immature, but they have a distinctly starchy flavor.

Mark Seeley's Weather Notes:
(Information provided prior to 8/16 rain in TC.)
The TC metro has not fully made up for the prior year precipitation deficit of 8-10". Since January 1, we are currently .6" below normal. Other parts of the state, most notably central and north central have been dryer, with 2-3" of storage soil moisture, compare to 3-4" in the Twin Cities. (Storage soil moisture is the moisture in the top 5 feet of the soil that is available to plant roots. )

Early this week (of August 15), the state will see 2 low pressure systems move through and they should bring some rain.

May through August has been cooler than normal. August 10th was possibly the coolest August 10th in Minnesota history with some places reporting temperatures in the 40s. The trend is for continued cooler than normal temperatures but not by 15-20 degrees, as seen the second week of August. This cooler weather has reduced the heat stress and moisture demands on plants, as we've not needed to water extensively.

There is no indication that this cool trend indicates an early frost.



August Garden Tips
Beth Jarvis, Yard & Garden Line

Cracking due to uneven watering Photo credit:
Beth Jarvis
Compiled from conversations with Dave Hanson, Urban Forestry, Bob Mugaas and Bob Olson, Regional Extension Educators and Deb Brown.

(These recommendation are based on Twin Cities temperatures. Adjust for northern Minnesota..)

Fruit:
Fruit Strawberry plants are actively setting new runners that will produce next year's crop. These runners need moist soil for the runners to set roots; dry, hard soil makes it difficult for these new plants to attach to the soil. Water your strawberry beds now, and continue to keep the beds actively growing as these new plants take hold.

Remove all over-ripe fruit to lessen the annoying picnic beetles.

Lawns:
Tis the season to be re-seeding! The next four week time period is the very best time to seed and repair thin spots in lawns. To get the grass estbalished quickly, be sure to maintain a damp seed bed. You will need to water once really well (soak) when you seed, then water it lightly one to two times per day, more frequently if the weather turns hot and dry. You keep watering until most of the seed has sprouted and is growing. This will take anywhere from a few days to two to three weeks.

Fertilize with one formulated for new lawns. Be sure it doesn't contain any pre-emergence herbicide or post-emergence herbicide. Apply it a rate of 1/2 pound of nitrogen per thousand square feet.

For information on fertilizing a newly seeded lawn:http://www.extension.umn.edu/distribution/horticulture/DG2923.html
For help with fertilizer calculations:http://www.extension.umn.edu/distribution/horticulture/components/1731-18.html

You can start to mow when the fastest growing grasses get a bit beyond the desired height. Mow to maintain the grass at the desired height. Overly-long new grass shades the ground and will prevent other grass seed from getting the sunlight cue to germinate.

If, after you've mowed 4-5 times, you spot perennial weeds, it will be ok to treat them with a post-emergent herbicide.

If you're thinking or core aerating or power raking/vertical mowing yout lawn, now's the time to line up the equipment for a fun filled Labor Day weekend!, now's the time to do it. Early Septmber is optimal time becauge the grass is growing so well tt that time. October will work but the grass grown is slower.

Then everything you ever wanted to know about lawn care and repair can be found at the Sustainable Urban Landscape Information Series website at: http://www.sustland.umn.edu/maint/index.html. Click on lawn maintenance and scroll down to the lawn care calendar for timing.

Vegetables:
Wilting tomato plants aren't always caused by fungal or bacterial infections. Another "common" cause of wilting is due to walnut toxicity. Tomato and potato are two of the most black walnut sensitive plants. The University's Plant Disease Clinic has confirmed several cases of walnut toxicity in plantings that previously appeared normal.

As some of your summer vegetables wind down, remove the plants and add them to your compost pile. Try to avoid composting diseased plants, as the heat generated during decomposition may not be high enough to kill the pathogens.

Watch for late-flushing weeds - especially winter annuals that germinate now and come back to haunt you next spring.

Coneflower with aster yellows. Photo credit:
Beth Jarvis
Flowers
It's ok to cut back any perennial foliages that has turned yellow or orange as the growing season winds down.

Deadhead (remove faded flowers) regularly as seed developmetn slows rebloom in annuals and wastes carbohydrates in perennial seeds.

Pull out and destroy any aster-yellows infected plants.Aster yellows is common on "blackeyed Susan" and many other flowers. See: http://www.extension.umn.edu/projects/yardandgarden/YGLNews/YGLN-Sept1502.html#BES
and:
http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-July1599.html#aster

Trees and Shrubs:
Water all your trees! Trees continue to need water as fall comes on. Turf grass will be in its most active period of root growth in Sept. and early October so it will be competing for water and nutrients.

Adequate soil moisture is critical now when trees and shrubs are begnning to going dormant for winter. Evergreens will need to be watered until the ground freezes. If you need a reminder on how to water trees, see: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Sept0103.html#water

Start getting quotes from certified arborists on tree pruning. Fall is a great to prune many trees and shrubs.

If less than 10% of an elm's canopy shows signs of flagging (yellowing, brown leaves on an individual branch or branches) preventative pruning together with injection of an approved fungicide by a trained arborist may save the tree. Certified arborists may be found at: http://www.isa-msa.org/MSA_Certified_Arborists.htm.

If you think you think your oaks might have oak wilt, contact your city forester or a certified ISA-MSA pathologist to advise you. Here's a list of city foresters: http://www.cnr.umn.edu/FR/extension/cityforesterlist.html

Editorial Notes

Liatris-a later summer native. Photo credit:
Beth Jarvis


A cyber pal in Hawaii asked me if Minnesota was vying with the Arctic for cold temps. While all the heat-loving garden plants have been shivering, the cooler than normal temps have been really nice for those of us who can or put up jam, jelly, preserves, etc.

I'm trying to pull together a series of what various plants are doing during the fall. The sections will deal with physiological changes that happen in the plants in response to changes in day length, light and sometimes temperatures. Some of these changes help them get through winter, some impact the following year's growth, etc. Bob Mugaas was getting all excited about writing about how fall sets the stage for turf grass to flower the following spring.

Anna's landscaping article will run later.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist


Beth Jarvis
Yard & Garden Line Project Coordinator


icon Previous Page
iconUniversity of Minnesota Extension Service Home Page
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request.  Please contact your University of Minnesota county extension office or, outside of Minnesota, contact the Distribution Center at (612) 625-8173.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.