|Yard & Garden Line News
Volume 6 Number 15 September 15, 2004
High Hopes for High Hoops
Robert Olson, Regional Extension Educator, Horticulture
This summer's dismal weather has prompted a lot of interest in garden structures that extend the growing season. Tops on this list are "high hoops" - also called "high tunnels" or "hoop houses". There names are interchangeable, and they've become the most popular form of greenhouse structure for many reasons.
Illus: Penn State
Basic structure, uncovered.
Field vs. tunnel tomatoes on Aug. 18, in Gr. Rapids
Up to 8# from some
indoor plants. None in field.
Onions: field vs tunnel-grown|
Tall enough for staked plants.
High hoops were originally designed for commercial growers, but their popularity has lead to the development of smaller structures that are being utilized by backyard gardeners. Regardless of size, the working principles are the same.
What are they?
High tunnels are unheated, plastic-covered structures that provide an intermediate level of environmental protection and control as compared to open field conditions and heated greenhouses. Plantings in high tunnels are placed directly into the existing soil of your farm field or garden, as opposed to production on benches or raised platforms like in greenhouses.
High tunnels are tall enough to walk in comfortably and to grow tall, trellised crops. Homeowner models that are 14 feet wide reach an interior height of about 8 feet; commercial models that are typically 30 feet wide reach a height of about 15 feet. The commercial models also have end panels that allow small tractors to drive through.
Greenhouses are permanent structures that are taxed as real property, whereas high tunnels (being temporary, moveable structures) are not. Greenhouses are covered by glass, rigid panels or double-layer plastic, but high tunnels are covered with a single layer of plastic.
A critical component of high tunnels is their ventilation system which generally consists of roll-up sidewalls that can be opened in the morning and rolled down at night or in cold weather.
Because the entire system is enclosed, no rainfall enters the tunnel. All water is supplied by the grower, generally via trickle tubes that are placed under plastic. The interior of the tunnel is completely dry and relatively clean. Harvested produce is very clean, greatly reducing the washing of produce. Research validates that fresh produce from tunnels also has enhanced shelf life as compared to field-grown produce.
Unlike commercial greenhouses that can cost up to $20 per square foot to construct, high tunnels can cost as little as $0.50 per square foot. This modest cost can result in a high return on investment, and in a season like this year growers with high tunnels reported that they paid for themselves the first season. Proponents of the tunnels see them as great income-generating technologies that college students and enterprising high-schoolers could manage as a summer job. One commercial-scale tunnel (30 feet X 90 feet), costing under $2000 to construct, could gross over $6000 if planted to tomatoes that are sold at farmer markets or roadside stands.
Everyone expected tunnels to provide a heat advantage compared to field-grown production. Few people, however, expected the dramatically reduced pest levels that are being realized. Growers and researchers alike are impressed with the excellent weed, insect, and disease control within the tunnels. Growers that have been cautious about organic production are now giving organics another look.
One of the most impressive features of these systems to date is the diminished disease pressure. The tunnel systems, by keeping the interior completely dry, result in an environment less conducive to several of the problematic disease organisms. Think about it, the foliage is always dry and there is no soil splashing compared to field grown systems. Add to this the wind protection factor from blowing soil and the enhanced vigor of plants, and you have an environment that allows crops to out-compete pests.
A critical component to managing diseases is the sidewall ventilation system. Without the open sides, the humidity levels would lead to a rainforest environment and subsequent disease haven. So during most days, the sidewalls are rolled open. When nighttime comes, the grower closes the tunnel to keep the cooler evening air from condensing on the leaf surfaces, thereby keeping the foliage completely dry. Just walk your lawn in bare feet after sundown and you'll know just how wet foliage can become. I'm reminded about condensation every winter morning when I scrape the ice from my car's windshield, whereas the cars parked in the garage are nice and dry. It makes me wonder, why is it that I am the one who pays for the cars, the insurance, the mortgage, and puts gas in the cars, yet I'm the one who has to park outside in the cold? I digress.
If your interest is piqued, you'll probably want to do a little research on the subject. My colleague, Terry Nennich, is developing a written manual on high tunnel management based on Minnesota research which will be designed for commercial growers. The principles will be applicable to the backyard gardener as well. Another great source for information is Penn State, which has a large research effort devoted to plasticulture, including high tunnels. They can be accessed at: http://plasticulture.cas.psu.edu/.
Golden Rust on Goldenrods
Janna Beckerman, Extension Plant Pathologist
Severe infection on goldenrod.
This year has been an interesting one for plant pathologists. As our long, cool wet spring, became a cool, dry summer, a variety of diseases that are commonly overlooked became unusually severe. One such disease is pine needle rust. However, the severity of this disease manifested itself most severely on the alternate hosts: Goldenrod (Solidago spp.) and Aster (Aster spp.)
To make sure the disease is rust, check your hands for spores,
but not while trying to take a photo at the same time!
When forest pathologists discuss pine needle rust, they refer to the economically important timber hosts of jack (P. banksiana), Austrian (Pinus nigra), red (P. resinosa), ponderosa (P. ponderosa), mugo (P. mugo), and Scots (P. sylvestris) pine. Economically speaking, the alternate hosts are of little value-except to the homeowner whose plant is suddenly orange. This disease is caused by the fungus Coleosporium asterum. Although it doesn't look that way, this rust causes little damage on either host. In pines, browning and needle death on lower branches is unattractive, and may slow the growth of young pines. On goldenrod and aster, severe infection may result in a reduction or loss of flowering.
The life cycle of pine needle rust takes an entire year to complete. Currently, on the aster and golden rod, we are seeing the uredinia developing on the leaves and stems. This stage can repeat itself under conducive weather conditions, and render the entire plant orange, as we've seen! Eventually, urediniaspores produce a new spore shape, the teliospore. The teliospores germinates to produce basidiospores that are windblown to pine needles, where new infections begin. These infections will not be seen until next spring.
In the meantime, the fungus survives winter in the infected pine needles. The following spring, small yellow spots appear on infected needles that develop into columns that split releasing orange spores. These spores are wind- dispersed and infect the underside of leaves of the goldenrod and aster. Orange structures called uredinia develop on the leaves and produce the characteristic orange spores that we are seeing now.
When diagnosing rust diseases, it is important to actually see spores! Plants turn orange for many other physiological reasons (nutrient deficiency, insect feeding, herbicide damage, etc.). Finding spores on your hands is a tell-tale sign to diagnose this disease!
Although pine needle rust rarely causes damage to mature trees, it can render plantings of asters and goldenrod unbelievably orange. Fungicides labeled for the control of rust on perennials contain active ingredients like sulfur, chlorothalonil, myclobutanil, and mancozeb. Replacing plants with rust resistant asters Removal of alternative hosts from the immediate vicinity of the trees will reduce infections of pines. Cultural practices such as thinning foliage, watering during dry periods, mulching, and fertilizing may reduce infections. Reportedly resistant goldenrod cultivars include: 'Baby Sun,' 'Baby Gold' and 'Goldkind.' The PREP trial in Rosemount has found that Aster 'Alma Potshke' was very resistant to rust, but that the A. dumosas series 'Wood's Pink' and 'Wood's Purple' were very susceptible and susceptible, respectively.
West Nile Virus Cases Down
Jeffrey Hahn, Assist. Extension Entomologist
Although many Minnesotans will think of 2004 as the summer that never was, we may also remember it for the low incidence of West Nile virus (WNV) that we experienced. Our first detected activity of WNV in Minnesota occurred in 2002 when we recorded 48 human cases and zero deaths. In 2003, the number of human cases tripled to 148 along with four deaths
The big question was what would happen in 2004. Would the number of cases continue to increase? Unfortunately, entomologists and vector ecologists don't know enough about this disease to accurately predict how the disease will cycle. But fortunately instead of continuing to go up, the number of WNV cases have fallen. So far this year, there have been only 19 cases and one death recorded in Minnesota (as of September 14, 2004). Although more cases are likely to be reported before the end of the year, (most cases in Minnesota are reported during August and September) the majority have undoubtedly occurred.
Interestingly, the number of horse cases this year are also considerably down. To date, there have only been 6 instances of horses infected with WNV. This is after 992 cases in 2002 and 74 cases last year. Although there may be several factors that help explain this, much of this decrease is probably attributable to the increased protection of horses that owners have given them, especially by vaccinating them.
However, there is not such an easy answer for humans to explain why the incidence of WNV has gone down. It is natural to assume that the cooler weather had a significant effect on WNV cases. While it is true the weather probably did slow down mosquito activity, it is unlikely the only reason. There does seem to be a consistent trend in other states for the rates of WNV to cycle down after a large increase of WNV has been first detected, although the exact reasons are not clear.
It is interesting to look at New York, the first state to record WNV. In 1999 they detected 62 human cases of WNV with seven deaths. Those numbers went down in 2000 to 14 cases, zero deaths and to 15 cases and two deaths in 2001. The number of human cases rose in 2002 to 83 (five deaths). In 2003, activity was down to 71 cases but with 10 deaths. So far in 2004 there have been only 5 cases with no deaths. Although the incidence of WNV may go up, it always seems to come back down to very small numbers. (Keep in mind that for a state with such a large population as New York, 100 or fewer cases is just a small percentage of the overall population).
There isn't an easy explanation for this pattern in New York or similar cycles in other states, including Minnesota. That makes it difficult to predict whether the current trend in Minnesota will remain in a downward cycle or fluctuate. The disease is too new here to understand it completely. We need to continue to learn about WNV to better understand what our potential risk may be.
For more information, see also the Minnesota Department of Health West Nile virus web site,
Get the low down on this month's insect pests at
Incorporate All-America Selections into Next Year's Garden
Deborah Brown, Extension Horticulturist
Gallardia 'Arizona Sun'
Vinca 'First Kiss Blueberry'
It's always fun to try new seeds, and when the flower or vegetable is an All America Selection winner, it's a pretty good bet that it will perform well in your garden. Here's a sneak preview of the All America Selections chosen for 2005. You should be able to order seeds from a number of mailorder or Internet catalogs. Some winners will also be available as young transplants in packs at local nurseries and garden centers.
Flowers: Gaillardia ‘Arizona Sun,' also known as "blanket flower," is a neat, compact cultivar suitable for container growing. Blanket flowers are usually short-lived perennials in our climate. Should you hope to over-winter it, plant it in the ground rather than in a container.
Catharanthus ‘First Kiss Blueberry,' usually called "vinca," is the bluest yet produced, but it's still a violet-blue rather than sky blue. Vincas have glossy, leathery leaves and can take sunny, hot, dry conditions. They also bloom in light shade, though not as well as in a sunny site.
Zinnia ‘Magellan Coral' produces double flowers, five to six inches across! It blooms early – only six to nine weeks from seed – and, like other zinnias, grows best when seeded directly into the garden.
Vegetables: ‘Fairy Tale' eggplant is pretty enough to categorize with the flowers instead of the vegetable winners. The petite plants produce small purple and white striped fruit that are tender and tasty when anywhere from one to four ounces in size.
‘Sugary' tomato produces grape-like clusters of ultra sweet "cherry" tomatoes that are oval, with a little point on the end. They can be harvested about sixty days after transplanting, and may be grown in large containers or supported, directly in the ground.
‘Bonbon' is a winter squash with an upright, semi-bush habit, requiring less garden space than most winter squash. The boxy, four pound fruits are said to have superior eating quality – sweet, with a creamy texture. They ripen roughly eighty-one days from planting, sometime the latter part of August in southern Minnesota.
Late September Garden Tips
Beth Jarvis, Yard & Garden Line
Compiled from conversations with Patrick Weicherding and Bob Mugaas, Regional Extension Educators.
These recommendation are based on Twin Cities temperatures. Adjust for northern Minnesota.
Trees and Shrubs:
Water trees, especially those 5 years old or less. Older trees, theoretically, could be damaged by heavy watering because it could prompt new growth that can't be supported by drought-damaged roots. However, recent substantial rains will lighten the drought stress on established trees, especially since they're shutting down in preparation for winter. Soil moisture is an important aid in the development of the abscission layer, so the rain will help the leaves fall. Drought stressed trees will hold leaves well into the winter.
Water all evergreens and young trees until the ground freezes. Water deciduous trees and shrubs as best you can until the leaves fall. Remember that lawn grass captures the vast majority of applied moisture, so water more than an inch within the dripline of trees. The soil should be damp at least 6-8". Plase see: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Sept0103.html#water"
Early fall color is a drought response indicating that the trees can't support the leave they still have. Poplars/cottonwood and ash are typical leaf "shedders" when stressed. Maples are another issue--that's maple decline--when trees are so stressed they can't recover.
Pruning for cosmetic or structural purposes should wait until the dormant season. Remove diseased trees now. Be sure all elm firewood has been de-barked before storage.
Hold off on pruning trees susceptible to fire blight right now. Wait until late winter. The most commonly affected are: pear, apple, crabapple, mountain ash and cotoneaster. Read about it at: http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p223fireblight.html
Shop fall tree sales. Pick well shaped trees with wide branch angles where applicable, and desired fall color. Plant in the ground by the middle of October.
Start thinking about rodent protection of new trees--it should go on before November 1, so shop around for 1/4" hardware cloth to surround tender-barked young trees.
It's a great time for perennial broadleaf weed control.
We're coming up to the tail end of seeding, though if it stays warm and rains, the rest of September could be suitable. Sooner rather than later is the key as grass needs to be established before winter's cold arrives.
Sodding can be done for another month or so.
If you overseed, work up the soil so you get good soil to seed contact. Tossing seed on a thatch-covered lawn will accomplish nothing.
You can start reducing mowing height. A 3" cut can be reduced to 2.5". This will reduce floppiness that can help reduce future snow mold problems and increase growing points/density of plants.
Be sure to water if we get into a dry spell, even though temperatures may be cooler.
Wait until closer to the end of October for the late season fall fertilizer application. If your grass is a bit anemic now, a half pound of nitrogen per thousand square feet of lawn could be applied now followed by the late fall fertilizer application of a full pound of nitrogen.
Core aerating is still possible. Dethatching should wait until spring. If you have heavy thatch, do a a real thorough core aerating job now. Grass needs 6-8 week of recovery time.
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.
Plant spring flowering bulbs soon. All but tulips need to be planted early. Tulips can be planted as late as you can dig in the ground. For more info, see Spring Flowering Bulbs http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h120bulbs-spring.html
As plants yellow and die back, it's ok to cut them back and compost any healthy plant tissue.
Joe Pye weed is noted for growing taller in the wild and staying shorter in cultivation. It could be a light issue, as wild plants may be trying to grow into more light. This photo, taken at Eloise Butler Wildflower Park many years ago, was in an opening in the woods and quite tall.
Joe Pye weed in wild
In the next issue, Bob Mugaas, Regional Extension Educator, Horticulture, will be writing about why lawns flower and set seed in the spring. The process starts in the fall. That will be published Oct. 1. I've asked a couple of grad students to write a piece on the physiological changes plants, other than turf grass, undergo in order to flower. In the future, Patrick Weicherding, Regional Extension Educator, Forestry, will be writing about new research findings on the timing of pruning trees for disease prevention and to prevent pruning damage.
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.
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