Rhododendrons and azaleas are spectacular flowering shrubs that add splashes of bright color to the landscape. Most that are common to northern landscapes bloom in the spring, although some summer flowering forms exist and can be used to extend the blooming season. What are commonly known as rhododendrons and azaleas are genetically distinct, but are both within the genus Rhododendron. They can be separated based on a number of features such as scales on the leaves and the shape and architecture of hairs. One very distinctive trait that holds true most of the time is that azaleas have 5 stamens, while rhododendrons have 10. Stamens are the male organs of the flower and terminate in a pollen filled sac called an anther. ‘Northern Lights’ azalea is pictured on the left (5 stamens) and ‘Olga Mezitt’ rhododendron on the right (10 stamens).
David C. Zlesak
According to the latest landscaping lingo, our decks and patios; places where people might have kept a metal dining set, a few pots of geraniums and a BBQ grill, have been upgraded to outdoor living rooms and kitchens. Front yards and back yards have become garden rooms and garden spaces. Anything to get people out and about with nature is great, whatever the name. Apply that thinking to herb gardens and imagine the possibilities! It’s not hard to envision an outdoor pantry, a healing spa, a crafter’s closet, or perhaps an open-air classroom.
Defined by the Herb Society of America as “plants for use and delight”, herbs are the original multi-taskers; grown for cooking, fragrance, medicine, crafts, wildlife, landscaping, and simply beauty. Although some gardeners like to grow themed herb gardens, they need not be confined to one spot in the landscape. Herbs make great groundcovers, excellent edging and mix well with flowers and shrubs in the border. Herbs lend themselves to container growing as well.
There are herbs for all conditions, however, most are happy with well-drained average soil, ample sunlight and water. That said, many of our best-loved herbs claim Mediterranean heritage; lavender, thyme, rosemary, sage and other gray-green or silver leaved plants will tolerate higher soil pH and lower water requirements. Important to these herbs is air circulation; crowding plants in humid conditions will promote fungal attack and rot. In some cases it is advisable to plant these herbs “high”; placing the union between stem and root somewhat above soil level with a slope of soil all around. A mulching of gravel around individual plants can help keep this area dry. It should also be said that this category of herbs is less attractive to deer.
While 6-8 hours of sunlight is optimal, a shady yard should not prevent gardeners from growing some herbs. Parsley, chives, lemon balm, chervil and some mints, among others will tolerate if not appreciate some shade, especially in the afternoon during hot summers. Container-grown herbs can go mobile to follow the sun.
Once established, many herbs can be considered low maintenance, the level of care corresponding to their purpose in the garden. A regular harvest of culinary herbs such as basil, thyme, tarragon, and oregano actually results in longer, better production. Pruning, no more than a third of the plant at one time, stimulates more leaf growth while staving off flowering and seed setting. In other cases herbs should be left to fulfill their growth cycle; seed production being desirable in herbs such as dill, fennel and caraway after having used their foliage too.
Ambitious gardeners can harvest herbs throughout the growing season for drying or freezing. Crafters will find art supplies right in their backyard; lambs ears (Stachys sp.), sweet annie (Artemisia annua) and roses (yes, roses are herbs) combine to make lovely wreaths. Textile artists can grow their own dyes with indigo (Indigofera tinctoria), woad (Isatis tinctoria), lady’s mantle (Alchemilla mollis) and yarrow (Achillea sp.) to name a few. Less energetic souls will find that the flowers, though small and not showy, are rewarding in themselves. The aromatic sprigs of many herbs are an unusual addition to garden-cut bouquets.
Let flowering herbs be and beneficial insects will be attracted to most herbal blooms, helping out with pest control. Beneficial insects, like ladybugs, lacewings, ground beetles and tachinid flies, are the reason behind much of the concept of companion planting. It is thought that certain vegetables grow better when planted near particular herbs. Tomatoes don’t thrive next to basil just because they think he’s such a nice guy! Instead they benefit when a braconid wasp, attracted to the basil flowers lays eggs upon the tomato hornworm’s back. These larvae will then parasitize the voracious hornworm upon hatching. That is the science behind the folklore in just one example.
Beyond beneficials, an herb garden will attract butterflies, birds, bees and hummingbirds. Herbs supply food for butterfly larva as well; dill, fennel and parsley being favorites. Determining which herbs attract which species is a great learning experience for children and adults.
Herb gardens can be as intricate as intertwining knot gardens, as simple as a pot of lavender on a sun-warmed terrace. Snipping a sprig of rosemary outside the kitchen door beats a trip to the grocery store. The scent of thyme crushed underfoot after a day at work is like a little aromatherapy session. Whatever “room” you make for your herbs, make room for herbs.
A list of herbs with proven success in Minnesota.
|Monarda (Bee Balm)||Rosemary|
|Salad Burnet||Summer Savory|
|*Marginal perennials that sometimes survive winters with adequate snow cover, mulching and careful placement (microclimate).
** Biennials treated as annuals.
In the early 1990’s the University of Minnesota initiated a hardy landscape rose breeding program. At that time the Canadian Explorer series breeding program was being closed due to the retirement of the breeder (Dr. Felicitas Svejda) and Agriculture Canada budget cutbacks. Dr. Svejda made great progress in her breeding program for landscape roses that possessed enough disease resistance and winter hardiness to make great, low-maintenance landscape additions in cold, Northern climates. Due to Dr. Svejda’s work and the work of other breeders, the popularity of hardy landscape roses in the North was growing and the University of Minnesota stepped in to help fill the need for continued cultivar development. After years of dedicated work, the first of the University of Minnesota releases from this effort are ready to be welcomed to our gardens- ‘Sven’, ‘Lena’, and ‘Ole’. These roses form the Northern Accents™ series and their names were selected as a playful way to celebrate our Minnesota culture and Norwegian influence. The creative marketing and jokes on the tags, like "One end smells good. Ya put the udder in da dirt" and "Uff-da" are spurring on chuckles in garden centers.
All three of these roses fit the polyantha (meaning “many flowered”) class of commercial roses. The polyantha class of roses began in the late 1800’s and are characterized by their compact, well-branched plant habit and abundant displays of small flowers (typically 1 to 2 inches in diameter) borne in large clusters. They are derived from climbing, cluster-flowered rose species from Asia (primarily Rosa multiflora and R. wichurana) and differ from these species primarily in their ability to rebloom throughout the growing season. With growth repeatedly terminating in flower buds and branching instead of producing ever elongating vegetative growth throughout the summer, most polyantha roses have lost the climbing nature of their species ancestors. They typically possess a compact, mounded to slightly spreading plant habit. Breeders have introduced additional traits such as wider ranges for flower color and form into polyantha roses through crosses with other classes of roses. Polyantha roses are known for their incredible number of individual flowers produced per plant. Polyantha roses can be found in the background of many of the landscape roses marketed today under the groundcover and shrub rose categories and their influence can be readily observed.
‘Sven’, ‘Lena’, and ‘Ole’ are all prolific bloomers and mature plants frequently have some open flowers on them at all times during the growing season. With today’s confined garden spaces and the popularity of container growing, these roses provide a great, versatile option. They can be nestled within the perennial garden and also serve similar landscape niches as other small flowering landscape shrubs such as compact potentilla, spirea, and weigelia cultivars. Compared to these other flowering shrubs, they have the advantage of a much extending bloom time and also an attractive fall fruit display.
Characteristics of each rose in the Northern Accents™ Series
‘Sven’ produces mauve/purple, double blooms. The exact shade of the flower color can vary throughout the growing season depending on growth conditions. Cooler temperatures in spring and fall lead to darker petal color and larger individual flowers. ‘Sven’ is the most fragrant of the three. The plant habit is rounded and plants typically grow to about 2.5 to 3.0 feet in height.
‘Lena’ is a spectacular single-flowered blush pink selection reminiscent of apple blossoms. It is similar to the popular old hybrid musk rose ‘Ballerina’, except hardier and more compact and manageable. Although all three selections have very good disease tolerance, it typically is the most resistant of the three to black spot. The plant is rounded in growth habit like ‘Sven’ and typically reaches 2.5 feet in height.
‘Ole’ is a semi-double blush pink rose fading to white. The dark blue-green foliage sets off the bright white/pastel pink blooms nicely. This rose produces flowers in very large clusters and produces the greatest number of individual blooms of the three. ‘Ole’ has a slightly more spreading growth habit of the three and typically reaches 2 to 2.5 feet in height and 3 feet in width.
‘Sven’, ‘Lena’, and ‘Ole’ are the first releases of the University of Minnesota rose breeding program initiated by Kathy Zuzek, scientist at the Horticultural Research Center and Dr. Harold Pellet. Dr. Pellet is probably most well known for his work with the Northern Lights series of azaleas. The Horticultural Research Center is home to a number of breeding programs including the famous apple and grape breeding programs and is located adjacent to the University of Minnesota Landscape Arboretum. Dr. Stan Hokanson is Dr. Pellets successor and now directs the ornamental woody plant breeding program. There are more rose selections, including additional polyantha roses and shrub roses, under evaluation.
Developing a new cultivar takes several years. Steps in the process include identifying parents that may be able to transmit desirable traits, making crosses, raising and evaluating seedlings, propagating the best performers for additional trials, determining which seedlings have consistent and superior performance, selecting the best performers as upcoming cultivars, wide scale propagation, and then patenting, marketing, and distribution. ‘Sven’, ‘Lena’, and ‘Ole’ were new seedlings in the breeding program in 1997. They were planted out in the field in 1998 and carefully observed until 2001, when the data supported they were consistently superior plants and warranted being selected for future trials. In 2003 enough plants were propagated for them to be put in regional trials in Morris, Grand Rapids, and Rosemount, Minnesota. They continued to perform well and deserved continued evaluation, unlike others which had too many disease issues or weren’t hardy or ornamental enough to continue. Bailey Nurseries trialed these advanced selections at their Minnesota facility as well. They are the commercial propagators and introducers of these roses.
When Zuzek began the rose breeding program there was a strong initial effort to characterize currently available roses for their adaptability to our climate and potential as parents. Much of the performance data of these roses as well as good general rose growing information is found in the book Roses for the North and can be accessed in its entirety online.
Ya, you betcha, ‘Sven’, ‘Lena’, and ‘Ole’ are a hardy bunch of roses that will make good, low maintenance landscape additions in Minnesota and beyond!
‘Frostbite’ has been around Minnesota for a long time, but hardly anybody knew about it. The small, sweet apple was bred by the University over 90 years ago, but it lived the obscure life of a breeding stock known by the unglamorous moniker MN447. All that changed, however, last fall, when the U decided to release the apple and held a public contest to confer a new name worthy of its flavor and hardiness.
Run by the U's Minnesota Landscape Arboretum, the contest had entries pouring in by the bushel--at least 7,000 all told. In late March this year, the appropriately Minnesota-y winning name was revealed. "The frost part signifies cold-hardy, and the bite part--we want people to do that," says U fruitbreeder and horticultural science professor Jim Luby, who coordinated the judging with apple scientist David Bedford of the University's 100-year-old Horticultural Research Center (HRC) in Chaska.
Apples of Their Ears
With 7,000 entries, the apple-naming contest turned up its share of colorful also-rans, many of which played on the apple's tropical flavor but northern lineage. Here are a few:
— Garrison Peeler;
— Alotta Colada;
— Arbor Eatum; and last but not least
— Last Tango in Embarrass
As Luby sees it, the contest was a way to give the public a peek "into the dressing room of a new apple before it hits the stage" of a public release. And one big part of making an apple stageworthy is the naming process.
Several people independently suggested ‘Frostbite’: Cindi Cardinal, an employee in the U's Como Recycling office; Lisa Rolf of Eden Prairie; Caroline and Ted Larson of Chaska; Ann Stout of Woodbury; Bonnie Winzenburg of Brainerd; Matt Zitzow of Roseville, Dianne Brackett of Wayzata; and Linda Davis of Coon Rapids. Each will receive a certificate and a basket of ‘Frostbite’s. Runner-up names: Munchkin and Small Wonder.
A Scrappy Survivor
The apple was bred at the HRC and bore its first fruit in 1921. For many years, University fruit breeder David Wildung kept a small orchard of ‘Frostbite’s at the U's North Central Research and Outreach Center in Grand Rapids, where it proved to be more winter hardy than any other apple released by the University.
Also, though small, the red-striped apple packs a wallop in the flavor department.
A Primer on Apple Breeding
Apple blossoms, explains Jim Luby, will only form fruit if pollinated by a tree of a different variety. But because the flesh of the fruit is produced by the maternal branch, it always matches the maternal variety, regardless of which variety supplied the pollen. The seeds within the fruit are hybrid, however, and will grow into trees bearing fruit with different traits from the maternal tree.
To preserve desirable traits, breeders propagate apple trees not by seeds but by grafting branches from the chosen variety onto rootstock. When mature, the branches will always bear apples with the same (maternal) flesh as the graft.
"Some people say it's like tropical punch," Luby says. "Some graduate students we get from the tropics say it's like chewing on sugar cane. To me, it's more like a pineapply, intense flavor. It has high acid, high sugar, and high fruit aroma. It's very intense--more than one would probably be too many for my taste."
In fact, says Luby, one reason its release was delayed so many years is that its strong flavor was thought to be a little much in an era when people were less adventurous about their food. Instead, ‘Frostbite’ found its main use in breeding; it was used to create the long-lasting Keepsake apple, and it is also a grandparent of ‘Honeycrisp’, now the official Minnesota State Fruit.
But times change, and people are now showing a wider interest in trying new delicacies. The decision to release the apple came partly in response to requests from nurseries about three years ago, Luby says.
In the meantime, the Arboretum has a few ‘Frostbite’ trees that bear fruit in late September and early October. And for those who find strong fruit flavors a little much, word has it that ‘Frostbite’ makes good cider and is also excellent for baking.
‘Honeycrisp’ and ‘Keepsake’ aren't the only other great apples to come from the U. University apple breeders have been in the business of breeding great apples for a long time.
Editor’s Note: This article first appeared as a UMNews article. It will take time for nurseries to propagate enough trees and for growers to raise them to fruiting size before ‘Frostbite’ apples will be widely available for consumption. This year’s supply of trees is already sold out and next year’s supply is also limited. In 2010 there should be large numbers of trees available for ‘Frostbite’ to be widely planted in both commercial and home orchards. Please be patient, the cold front is coming and soon we’ll experience ‘Frostbite’!
Although many fungal diseases in the flower garden do not get going until warm humid days of summer, Botrytis blight attacks peonies even as they emerge from the ground.
Gardeners with Botrytis blight will notice that young peony shoots will grow 6-8 inches and then suddenly wilt and fall over. Close examination of these fallen shoots will reveal a dark brown to black soft sunken area on the stem right around the soil line. Under humid conditions, a dense velvety mat of gray spores will be present on the infected part of these stems. These spores are characteristic of Botrytis blight, caused by Botrytis paeoniae, and should be taken as a warning of future problems.
Botrytis paeoniae only attacks peony plants. It thrives in cool wet weather (60°F is perfect) and often attacks young shoots as they emerge from the ground in the spring. The spores that are produced on these early infections can spread to other parts of the plant by wind, rain, or insects. Botrytis blight often blasts young flower buds, causing them to turn black and dry up before they ever open. Large irregular brown spots can also occur on petals of open flowers and on leaves. Infections from buds and flowers often continue down the peony stem turning it brown or black. In severe cases the infection, it can move into the roots and crown of the plant resulting in rot, although this is not common. Botrytis blight can spread throughout the summer whenever cool wet weather is present. It may not be seen at all in hot dry years.
For gardeners dealing with Botrytis blight of peony, sanitation is the best defense against future flower and leaf infections. The Botrytis blight fungus produces an abundance of spores on infected plant material whenever moisture is present. These spores spread the disease to other plant parts. It is therefore critical to remove all infected plant parts from the garden as soon as possible.
Choose a dry day when spores are less likely to be present. Take a paper bag to the garden and cut out any infected plant parts, placing them immediately in the bag. For infected young shoots, cut out as much of the infected stem as possible without hurting the crown of the plant. This may mean excavating an inch of soil from the base of the infected shoot to make a clean cut. If any dried stalks from last year remain around the base of the plant, remove these as well. At the end of the summer, the Botrytis blight fungi makes hard resting structures called sclerotia that allow it to survive MN’s winter on last years infected stems.
If flower buds or leaves become infected later in the season, they should also be promptly removed from the garden. In gardens where Botrytis blight has been a problem in the past, it is a good idea to collect and remove faded flowers as well, since the fungi can easily colonize the old flower petals and produce spores. Do not compost these diseased plant clippings, as the Botrytis blight fungi can survive and even grow within the compost pile. Instead, throw these infected plant parts into the trash.
Reducing moisture on and around the peonies will also help minimize problems with Botrytis blight. Avoid using dense wet mulches like composting leaves, around the base of the plant. Choose instead mulches that allow air to pass through to the soil like large woodchips or bark pieces. Pull mulch away from the immediate base of the plant so that air moves by stems. In plants suffering from many infected shoots, it may be worth while to remove old mulch and discard it like the infected plant material, since the fungi can survive in organic material. Replace the old mulch with fresh airy mulch. As with any fungal leaf blight disease, using drip irrigation or soaker hose instead of sprinkler irrigation will help to keep foliage dry and reduce disease.
One of the more common tree insect pests is the European pine sawfly. Depending on the weather, they can emerge anytime in central Minnesota (including the Twin Cities) from early to late May. Because of this year’s cool spring, the first report of European pine sawflies did not occur until May 21. You can recognize this insect because it is caterpillar-like, has eight prolegs on its abdomen, has a dark colored head, and a gray green body with light green stripes. They are about 1/16 inch when they first hatch and grow to be 3/4 - 1 inch as fully grown larvae.
European pine sawflies feed for about six weeks on the old needles of mugo pine and other pine species, including Scotch, Austrian and red. Although an evergreen can better tolerate feeding damage restricted to the old growth compared to the new growth, these needles are not replaced and when defoliation is severe. It can stress trees and shrubs and make them unattractive.
Although these sawflies have been active for about 10 days (as of June 1), there still can be time to treat them, depending on how large they are. Ideally, you want to treat sawflies when they are at half full grown length or less. For European pine sawflies, if most of the larvae you see are 1/2 inch or less and damage is not too severe yet, it should be worth your while to treat. Once these sawfly larvae are about 3/4 inch long, it is not effective to treat them.
Inspect your pine not only for presence of the sawflies but also check for missing needles which could be a sign of sawflies. They are gregarious which means they will feed in nonsocial groups so you can find many on one or two branches and few or none on the others. If you discover you have a European pine sawfly infestation and they are small enough to make it worth treating, you have several options to deal with them.
One nonchemical option is to physically remove them. You could do this in one of several ways. You could spray them off with a hard stream of water from the hose. That does not necessarily kill them but they will have a hard time getting back on the plants. You could pick them off and drop into a pail of soapy water. For those that are not too squeamish, you can don your rubber gloves and run your hands over the infestation, crushing them.
There are also several low impact insecticides you can use if you don’t want to try physical removal, such as insecticidal soap. It is important to hit the larvae directly with the spray for it to be effective. Also, there isn't any residual activity so you won't kill sawflies that walk onto treated needles later and may need to repeat the spray. Another effective, low impact product is spinosad (e.g. Conserve) which is effective for leaf and needle feeding insects and has some residual activity.
It is important to note that Bacillus thuringiensis, an effective low impact insecticide on caterpillars, does not work on sawflies. While caterpillars and sawfly larvae look similar, they are very different insects and Bacillus thuringiensis only affects caterpillars and not sawflies.
If you prefer to apply a longer lasting residual insecticide, there are a variety of garden products available that would work against sawflies such as esfenvalerate, bifenthrin, permethrin, and carbaryl (Sevin). Products containing these active ingredients are commonly available.
If your tree is too large to get good coverage another option is the systemic insecticide imidacloprid (e.g. Bayer Advanced Tree and Shrub Insect Control). You apply it to the ground at the base of the tree or shrub and the plant absorbs it and carries the insecticide to the needles. A drawback is it takes time for the product to be carried through the tree; the larger the tree the longer it takes. It can take weeks or more. It is too late to treat your trees this year for European pine sawflies. However, if you have an ongoing problem with them, then you can treat your plants during the summer or fall and it will control the sawflies next spring.
The cool, slow spring has been wonderful to extend the display of spring flowering bulbs. Most of the daffodils are finished blooming and some of the late flowering tulips are still holding on as well as grape hyacinths. If you hope to keep your bulbs and have them flower next year, allowing the foliage to naturally die back is important so they can produce and store as much energy as possible. Spent blooms can be removed to tidy up the plants and allow more energy to go into bulbs versus seed production. To help mask the old foliage of bulbs, consider interplanting with other plants. They will provide a nice succession, filling in the space occupied by the bulbs as the bulbs eventually die back completely in late June or July. Consider annuals for interplanting, or if bulbs are part of an established bed of perennials, neighboring perennials can be carefully chosen that emerge relatively late like hardy hibiscus. Some advocate creatively braiding the narrow leaves of bulbs such as daffodils for added ornamental interest after flowering. Although interesting, this interferes with access to light and can reduce the amount of energy able to be generated.
Even though it has been a cold spring and slow start to the growing season, we should finally be experiencing warm enough temperatures to plant out our warm season crops. This includes impatiens, morning glories, tomatoes, cucumbers, peppers, and melons. When raising vining crops, it is often easier and produces less damage to put stakes, cages, or other support structures in place before planting or when the plants are still small. Waiting until plants are larger increases the risk of damaging them as we dig near them or try to redirect their growth.
Select bedding plants that are not overgrown and look vigorous and healthy. Avoid plants that appear to have experienced stress. Common signs of stress include dry, dead leaf margins suggesting a time when the plant dried out too much between waterings; light green, stunted growth that may indicate nutritional problems; and light green stretched growth because of inadequate light common on the stacked shelves in some retail settings. Bedding plants that are heavily pot bound and have an excessive amount of open flowers on them should also be avoided. The goal is to select vigorous plants that will transition smoothly into our gardens and continue growing strong.
Although we didn’t experience excessively cold temperatures this past winter, we did have periods of relatively cold temperatures over extended periods of time. This along with other factors has led to many shrubs and trees with odd sections of dieback. As the temperatures have warmed, we are eventually seeing which stems have survived and are producing viable growth. Compromised stem tissue may have allowed for some new growth to begin, but as temperatures finally warmed they may not be able to keep up with moisture demands. Carefully reassess pruning needs and remove what has recently died or is weak and unsightly.
If you have missed the window of opportunity to treat your lawn with a preemergent herbicide for crabgrass, there is still another opportunity for control. There are some postemergent herbicide products labeled for control of emerged crabgrass in lawns. Those products labeled as grass killers or broadleaf weed and grass killers are usually designed to kill all kinds of grasses, including lawn grasses and not just crabgrass and should be avoided. When treating crabgrass after it has emerged, be sure that the desirable lawn grasses are not under any kind of heat or drought stress as you can sometimes cause temporarily yellowing. Under severe stress, permanent injury can also occur to our lawn grasses. Please read and follow the label. As with most weed control options, treating the plants while they are small and tender is generally more effective than trying to control larger, more mature plants.
Lawn grasses will usually have better stress tolerance when they are mowed higher from the middle of spring through early fall. Higher heights of cut usually mean at or above 2.5 inches for most lawn grasses. This helps encourage deeper, more robust root systems capable of extracting water and nutrients better. Access to more soil moisture and nutrients increases the plants capacity to tolerate and survive the frequent hot and dry periods of late spring through summer.
With so many yard and garden chores needing to be completed during a typical Minnesota May and June, it is very easy to overlook the water needs of our lawn grasses, trees and shrubs, and gardens. However, it’s important to remember that May and June are very active months of growth for plants. For most plants an ample supply of water typically means 0.75 to 1.0 inch of water per week. If rainfall is not sufficient, supply the remainder through irrigation. Consistent, deep waterings are especially important for new or recently planted trees and shrubs and newly planted seeds and transplants.
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David C. Zlesak, Ph.D.