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Extension > Yard and Garden News > December 2012

Monday, December 3, 2012

December 1st 2012 Issue

In this months issue:


Christmas rose (Helleborus niger)

Position your houseplants to avoid winter starvation

Still time for sanitation

Bed bugs and Bombs

2013 Gardening Calendar





Karl Foord


Karl Foord


Karl Foord


Karl Foord


Karl Foord


Karl Foord


Karl Foord


Karl Foord


Christmas Rose (Helleborus niger)

Robin Trott, University of Minnesota Extension Educator

I know the growing season is officially over when we make our annual trek to the Association of Specialty Cut Flower Growers conference. This time we travelled to Tacoma, WA, and had the great pleasure of visiting growers in the Skagit Valley, north of Seattle. This year's particular delight was visiting Skagit Gardens and beholding their greenhouses filled with hellebores.

Skagit Gardens

Photo 1: Skagit Gardens Greenhouse of hellebores

Skagit Gardens

Photo 2: Skagit Garden's Greenhouse of hellebores

This alpine plant grows native at high elevations and produces large white flowers that turn a blushy pink as they age. Until recently, these perennial plants (hardiness zone 4-9 depending on species) were the sole domain of rare plant collectors, with prices way beyond the pocket book of average consumers. With the breeding programs developed at Skagit and other wholesale nurseries, a variety of cultivars are available at garden centers nationwide.

Hellebores are anatomically separated into 2 groups, "caulescent" and "acaulescent". Caulescent hellebores are those with above-ground stems (Figure 1). Acaulescent plants are those where the flowers are born on their own stalk with no leaves, and the leaves have their own stalk (Figure 2). Caulescent varieties are popular for use by florists in dramatic arrangements.

M. Talt (

Figure 1: Caulescent Species of Helleborus

M. Talt (

Figure 2: Acaulescent Species of Helleborus

The Christmas rose is the best known and certainly the showiest of the species hellebores (Photo 3).

Skagit Gardens

Photo 3: Christmas rose (Helleborus niger)

Easier to grow than the ever popular "Poinsettia", plant breeders like Skagit are hoping to promote this flower as the new and improved holiday potted plant which can later be transplanted in perennial beds to bring joy year after year.

If you select a hellebore as a holiday accent this year, keep these horticultural tips in mind:

For indoors care, keep your plant in a bright cool location, away from any heat source. (Hellebores will bloom through snow, they like it cold!) Keep the soil moist; don't let the plant dry out! Don't worry if your hellebore gradually yellows, this is natural. If you are concerned, move it to a cooler location. Plant your hellebore outside in partial to full shade as soon as the ground has thawed. Protect your transplant from weather extremes until it has become established.

Once transplanted, mulch your hellebore to keep the soil cool and moist throughout the summer months. Make sure you have selected a site that is protected from desiccating winds. The new breeding of these beauties has made them disease and insect resistant. Once established, they require minimum additional care. Deer don't touch hellebores, which is an added bonus to this delightful flowering plant.

Although each variety holds it blooms for a lengthy period, during which time the flowers turn from pure white to pinkish green, you can increase your bloom time by selecting several different cultivars.

Jacob: the traditional "Christmas Rose" will bloom as soon as the frost begins to leave the ground in the spring. It is a compact plant (9-12"x 13" spread) with pure white slightly fragrant blossoms atop burgundy stems.

Skagit Gardens

Photo 4: 'Jacob' Lenten Rose (Helleborus niger 'HGC Jacob')

Josef Lemper: another Helleborus niger is a taller (15-18"x 21"spread) early bloomer.

Skagit Gardens

Photo 5: Josef Lemper Lenten Rose (Helleborus niger 'HGC Josef Lemper')

'Winter's Bliss': Is a later blooming variety whose large white blossoms fade to deep pink with age. It grows 15-18" with a 24" spread.

Skagit Gardens

Photo 6: 'Winter's Bliss' Lenten Rose (Helleborus x ericsmithii 'HGC Champion')

Joshua is a 12-15" early blooming variety with a 17" spread. Its slightly fragrant white blooms age to light green. Its foliage is glossy dark green and works well as filler in your springtime arrangements.

Skagit Gardens

Photo 7: Joshua Lenten Rose (Helleborus niger 'HGC Joshua'

Silvermoon: (15-18"x21") has creamy blossoms tinged in pink atop rose colored stems.

Skagit Gardens

Photo 8: 'Silvermoon' Lenten Rose (Helleborus x ericsmithii 'HGC Silvermoon'

This is just a small sampling of varieties that are hardy to USDA Zone 4, and thrive in Minnesota Gardens. Check with your local garden center this spring for varietal availability.

Position your houseplants to avoid winter starvation

Karl Foord - Extension Educator, Horticulture

Light Basics

Note: Measurement of light is a complicated subject. This article can be approached from at least two levels: one level would be to gain an intuitive sense of the graphs, whereas a second level would be a more in-depth approach where individual parameters are explored. For those interested in the latter, references are given at the end of the article.

In Minnesota the number of hours of light essentially doubles between the winter and summer solstices, 8 and 16 hours, respectively. (Figure 1).

M. Pidwirny (

Figure 1: Hourly variations in insolation received for a location at 45° North latitude over a 24 hour period.

The low angle of the sun reduces the number of light photons or energy per unit area meaning that the energy received at mid-day on December 21 is less than one third of that received at mid-day on June 21 (Figure 2: Sun declination angle relative to energy received at 41.7 o N latitude).

Apogee Instruments

Figure 2: Season Comparison of Solar Zenith Angles in Logan, Utah 41.7 degrees N Latitude

In fact the total light energy received in December on average is closer to one quarter of that received in June and July (Figure 3: outdoor daily light integral US).

J. Faust

Figure 3: Outdoor Daily Light Integral U.S.

To survive the winter we bring our plants inside and further reduce light reception through the shading effects of the building. Because plants use light to produce needed metabolic compounds such as sugars and starches, this drastic reduction in sunlight means we have the opportunity to starve our plants.

Plant Selection

To have a good experience with houseplants, we need to choose those plants that can tolerate these "lean" conditions. I have two categories of houseplants, plants that stay inside year-round, and plants that winter inside and summer outside. In the first group I have had success with: African violets (Saintpaulia ionantha), Phalaenopsis orchids, cacti, Cyclamen (Cyclamen persicum), Schefflera (Schefflera actinophylla), and Norfolk Island pine (Araucaria heterophylla). In the second group I have had success with Meyer lemon (Citrus × meyeri), tropical hibiscus (Hibiscus rosa- sinensis), banana (Musa 'Dwarf Cavendish'), pygmy date palm (Phoenix roebelenii), and cycad (Cycas revoluta). All of these plants have the ability to tolerate lower light conditions.

Match your home micro climates to the plants' needs

The best way to handle this is to understand the light needs of your plants and the amount of light entering your house through various windows. The amount of light energy is greatest from the south > west > east > north. In the winter the sun rises south of due east and sets south of due west. Windows facing directly east and west receive sun coming at an oblique angle to the window, reducing energy received.

Karl Foord

Photo 1: Houseplants in south and west corner window BEFORE

I have placed my African violets (Saintpaulia ionantha), Phalaenopsis orchids, cacti, and Cyclamen (Cyclamen persicum) in a corner with south and west facing windows. These plants stay here year around and avoid direct summer sun due to plant and building shading effects (photo 1).

Karl Foord

Photo 2: Houseplants in south and west corner window AFTER

To improve the location I washed the windows and re-potted the orchids to improve spacing (photo 2).

Karl Foord

Photo 3: Houseplants in west window BEFORE

The other plants [Meyer lemon (Citrus × meyeri), tropical hibiscus (Hibiscus rosa- sinensis), banana (Musa 'Dwarf Cavendish'), and pygmy date palm (Phoenix roebelenii) have been placed in western facing windows.

Photo 3 shows the decrease in light level from the center of the room to the window, a 36 fold decrease.

Karl Foord

Photo 4: Houseplants in west window AFTER

Photo 4 shows the plants positioned to optimize their light reception.


Recognize the @ 75% decrease in light energy received from summer to winter solstice. Choose plants that tolerate lower light levels and select locations in your house affording plants adequate light. Recognize the dramatic reduction in light energy as you move away from the window.


Korczynski, P., J. Logan, and J. Faust. (2002). Mapping monthly distribution of daily light integrals across the contiguous United States. HortTechnology 12 (1) pp. 12-16.

Lopez, R. and A. Torres. (2010). Measuring daily light integral in a greenhouse. Commercial Greenhouse Production. Purdue Department of Horticulture. Bull HO-238-W (accessed 12/2/2012)

Pidwirny, M., and S. Jones (2010). Daily and annual cycles of temperature in Chapter 7: Introduction to the atmosphere in, Fundamentals eBook.

Sunmaster (2012). PAR Watts, Lumens, Photons, Lux and Watts.

Still Time for Sanitation

Michelle Grabowski and Jeff Hahn, UMN Extension

M. Grabowski, UMN Extension

Photo 1: Dead daylily leaves with visible dark spots from daylily leaf streak

The ground is cold, trees have dropped their leaves, and perennial and annual flowering plants have died back to the ground. Yet there is still time for a garden clean up that will reduce the number of pathogens and insect pests that survive from this season to the next. Sanitation, the removal of a infected plant material, is one of the basic steps of integrated pest management. It is a chemical free way to reduce pest damage in future growing seasons.

For sanitation to work you must remove the part of the plant that is infected with a pathogen or insect pest completely from the area and destroy it. Disease infected plant material can be burned, buried or composted. Check with local laws about burning plant material. Composting will kill pathogens and insects only if the pile gets hot. If your backyard compost pile is a slow pile of cold rot, consider taking infected material to a municipal compost site. These sites have so much plant residue to work with they manage the pile to heat up so the material breaks down quickly. It is important to realize that it might take a few years of good sanitation to truly get ahead of a fungal or bacterial plant disease. Fungi are known to survive 2-4 years in buried plant debris, bacteria typically can survive 1-2 years.

Here is a list of a few plant problems that would benefit from fall sanitation efforts.

M. Grabowski, UMN Extension

Photo 2: Fallen leaves at the base of this rose shrub should be cleaned up and removed from the garden to prevent overwintering of black spot

Trees and Shrubs
Apple Scab on crabapple or apple trees
Black Spot on rose
Any leaf spot disease like tar spot on maple, anthracnose or linden leaf blotch
Rake up and remove those leaves or they will produce fungal spores to start next years epidemic!

In the Flower Garden
Fungal and bacterial leaf spot diseases on perennials like Botrytis leaf spot on Peony, Daylily leaf streak, Iris leaf spot. Sorry, but sanitation will not help reduce powdery mildew.
Remove plants at ground level. Clean up all stems and fallen leaves. The pathogens survive in any infected plant material.

Four Lined Plant Bug
Iris Borer
These insects lay eggs on plant material late in the growing season. In spring the new insects cause damage on these plants.

In the Vegetable Garden
Septoria Leaf Spot on tomato
Early Blight on Tomato
Bacterial leaf spot on pepper
Remove plants at ground level. Clean up all stems, fallen leaves, and rotten fruit. Infected plant material can be removed from the garden or tilled under.

Squash Bug
Asparagus Beetles
These insects spend the winter as adults under plant debris. By removing plant debris in general the number of overwintering sites for these insects is reduced.

Bug Bombs and Bed Bugs

Jeffrey Hahn, Asst. Extension Entomologist

The resurgence of bed bugs in the U.S. over the last 10 or so years has increased many people's awareness of these biting insects. They have presented residents and pest management professionals a tremendous challenge to detect and eliminate them. A popular tactic used by residents in bed bug control is the application of total release foggers, also known as bug bombs. Many people have turned to these products to help them control their bed bug problems. But are they effective? This question was examined in a research study conducted by Drs. Susan Jones and Joshua Bryant at Ohio State University.

Jeff Hahn

Photo 1: Bug bombs are not effective in controlling bed bugs. One reason is the insecticide does not reach where the bed bugs hide.

They compared three popular bug bombs that are available to residents. The Hot Shot Bedbug and Flea Fogger is specifically labeled for control of bed bugs and was more extensively tested. They also examined the Spectracide Bug Stop Indoor Fogger and Eliminator Indoor Fogger. Although these products are not listed specifically for bed bugs, they are labeled for flying and crawling insects and could be used by Minnesotans in an attempt to eliminate bed bugs.

Jones and Bryant tested these products against five different populations of bed bugs collected from home infestations in Ohio. They also tested these bug bombs against a strain of bed bugs that has been reared exclusively in a laboratory for 39 years. These bed bugs have never been exposed to pesticides and are susceptible to bed bug products. All of these bed bugs were exposed to the Hot Shot Fogger in three scenarios, direct exposure, optional harborage (they could hide under filter paper), and forced harborage (they were covered by a thin fabric covering). The other two foggers were used only in direct exposure and optional harborage experiments (they were unable to complete the Eliminator Fogger and optional harborage trial) against two of the field collected bed bugs as well as the continuously lab reared bed bugs.

All three bug bombs had generally little effect on the 'wild' collected bed bugs in the direct exposure experiment (with one moderate exception). However, most or all of the lab reared bed bugs were killed. Similar results were seen in the optional harborage experiment except that it took longer to kill most or all of the lab reared bed bugs. In the forced harborage trial, all bed bugs, including the susceptible lab reared bed bugs, were minimally affected by the Hot Shot Fogger.

So what does all of this mean? The short answer is that bug bombs are not effective in controlling bed bugs. There are several reasons why this is true. First, the bed bugs that we battle in our homes are generally not affected by the insecticides contained in bug bombs, even if they are directly exposed to them. There has been growing evidence of varying degrees of bed bug resistance (i.e. they are much less vulnerable) to pyrethroid insecticides which is the primary active ingredient of bug bombs. Only bed bugs that have never been exposed to insecticides could be easily killed and then only if they were directly exposed or were exposed before they sought a place to hide. This research project also concluded that bug bombs were ineffective because of short exposure times, the low concentration of insecticides, and the lack of residual activity.

Bug bombs are also not effective because the insecticide does not penetrate to the harborages where bed bugs hide. This is critically important as these biting insects spend most of their time hiding in cracks, tight spaces, behind and under objects, and similar places (up to 80% of them hide in harborages during the day). They are infrequently out in the open for any length of time and even then just a few at a time. For bug bombs to be effective, they need their target insect to be out in the open long enough for the insecticide to reach them. This research also found that even the susceptible populations of bed bugs were largely unaffected when they were in protected sites.

While bug bombs are not the answer, there are a lot of positive steps you can take to help control a bed bug infestation. See the University of Minnesota's Let's Beat the Bed Bug web page. From there you can access a variety of fact sheets and other sources of information as well how to contact the Bed Bug hotline.

The results of this research were published in the Journal of Economic Entomology, 105(3): 957-963 (2012).  A summary of this research was also published in Pest Control Technology in the October 2012 issue.
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