Home « Gardening News « August 15, 2007

Yard and Garden News

Have you ever visited a garden center or nursery with the intention of just buying potting soil, and you walk out later with a dozen new plants, telling yourself confidently “I’ll find a place for them”? Having a fairly short growing season, Minnesotans tend to want to try growing … everything! However, next to soil preparation and quality, poor plant selection most often leads to an unsustainable landscape – and a lot of stressed plants that struggle to survive in the wrong conditions. So here are some guidelines to remember as you peruse your local garden center that will save you time, money and frustration while helping you create a great looking AND sustainable landscape.

Tip #1: Size is everything
Mature plant size is the #1 thing people tend to ignore when selecting plants. The plants we purchase tend to be young and need a few years (at least) to reach their mature size. Often people don’t want to wait several years for a landscape to fill in, so they will space plants too close to each other, or the house, the sidewalk, or the street only to remove them later because they are blocking a window, a walkway, or a door. Space plants according to their mature size, not the size they are at the time of purchase, and be patient. They’ll grow.

Tip #2: Believe the plant tags
Plant tags are not just for marketing and attracting attention. They provide valuable information from the grower that needs to be noted by the buyer. These plant tags usually note plant characteristics such as mature size and spacing (see Tip #1) as well as site requirements such as soil type, light and moisture. Likewise, they often give the buyer good planting instructions and some background on the plant itself. Plant tags: read ‘em. Believe ‘em.

Tip #3: Know your soil
Would you ever want to build a house with a poor foundation? Of course not. So think of soil as the foundation of your landscape and get to know it by taking soil samples. The University of Minnesota Soil Test Laboratory will test your soil for a small fee and provide a wealth of information including what your soil contains and what your soil is lacking. Apply this information by amending your soil and creating a good home for your plants. Then select plants based on your soil type. Try the native dwarf bush honeysuckle (Diervilla lonicera) for dry, hot areas along streets and sidewalks. You may also decide to select some plants that require extra care such as the popular U of M Lights Series azaleas that require an acidic soil pH and a little extra maintenance (see Tip #9). By understanding your soil, you are on your way to proper plant selection.

Access information on how to submit a soil test by visiting the University of Minnesota Soil Testing Laboratory http://soiltest.coafes.umn.edu/.

Tip #4: Watch the sun
Pull up a lawn chair, get a cold drink and the latest Yard & Garden News, and watch how the sun moves across your landscape. A plant requiring “full sun” typically needs 6 or more hours of full sun per day. “Part sun” means about 3 to 6 hours a day, “full shade” means the plant receives no direct sun at all throughout the day (Designing and Preparing a Perennial Bed). You may want to have a sketch of your landscape and note the hours of sunlight that various areas receive. Be sure to notice how shrubs and trees, new or existing, will change the light available to understory plants as they mature. Also, some plants will tolerate more or less sun than they’d prefer, but their performance may be hampered. They may not bloom as prolifically or the foliage may become “sunburned” (dry patches). Likewise, while a plant may produce more blooms in full sun, the blossom color may not be as intense.

Tip #5: Locate plants according to water needs
Xeriscaping refers to designing areas of landscape that don’t require supplemental irrigation and uses techniques such as hydrozoning (grouping plants in a landscape according to moisture requirements), minimizing turf areas, efficient application of water, and of course, plant selection. Although we live in the land of 10,000 lakes, gardeners and landscape designs need to be diligent disciples about conserving our most important natural resource: water. Our climate is becoming drier overall, and thinking about using less water in your landscape will help make better plant choices.

Tip #6: Stay in your zone … usually
The USDA Plant Hardiness Zone map can be found in just about every gardening book published as well as on numerous websites. According to the USDA, Minnesota ranges from Zone 4b along the northern Iowa border to Zone 2b in Pinecreek, MN, in Roseau County along the border of Manitoba. These zones are based on the average annual minimum temperature in a given region, but soil moisture, snow cover, and overall plant health are important additional factors that can affect winter survival. (U Horticulturists Urge Caution on new hardiness zones) Plant breeders have used these zones to classify plants as being hardy for a certain region and to give the consumer an indication of winter survival. Experts recommend erring on the side of caution and selecting plants proven to be hardy in your region. That said, an adventurous gardener may try out a plant specified for Zone 5, and depending on the harshness of the winter, the planting conditions and with some extra TLC, some may survive (but you didn’t hear it from me).

Tip #7: Determine the plant’s purpose in the landscape
“Right plant, right place – right purpose”. Every plant should have a design purpose in a landscape. Some plants provide accent and help guide people through a landscape. Other plants are key plants and are located near building corners, fence posts, and gates to soften the harsh vertical lines of these structures. Some plants make great mass plants. Mass plants have the job of providing unity and continuity within the areas of a landscape. Specimen plants are the “drama queens” and are charged with bringing fabulous flowers, foliage, fruit, etc. to a landscape.

Tip #8: Mix plant form, textures and colors
When selecting for a landscape, a plant’s characteristics should fit the plant’s purpose. For example, accent plants provide year-round interest, so they are often evergreen or have interesting bark or form. A popular and common accent plant is the hardy Medora juniper(Juniperus scopulorum ‘Medora’). Blue foliage and a strong vertical form make it eye-catching in the landscape. Specimen plants are often very showy during one or more season. One of my favorite summer specimen plants is the hardy hibiscus (Hibiscus moscheutos ‘Cristi’) planted in our display and trial garden on the St. Paul campus. Mass plants are fine-textured and grow together into one mass, losing their individual form. Tiarellas or foam flowers mass nicely together, come in lots of foliage colors, and have great flowers.

Tip #9: Maintenance: How much do you want to do?
All plants require some level of maintenance, but some may require a little more maintenance than others. Decide how much time you want to devote to meeting special plant needs and then take that into consideration when selecting plants. For example, the popular Endless Summer® hydrangea requires an acidic (low pH) soil in order to produce those gorgeous sky-blue flowers coveted by many. Unless you have acidic soil to start with (unlikely in most Minnesota gardens), the pH will have to be adjusted through soil amendments by the gardener. This will entail some extra time, money, and dedication. However, Endless Summer® hydrangea will produce pale pink to dark pink blooms when planted in neutral to alkaline (high pH) soil – and they are equally lovely, if expectations are adjusted accordingly. Other plants may require carefully timed pruning in order to preserve the next year’s flowers. Our common lilac is in this category. Lilacs set flower buds for next year within two to four weeks after blooming. So if you need to do any major pruning, do it within those few weeks to avoid pruning off next year’s flower buds (and isn’t that really why we grow lilacs in the first place?)

Tip #10: Keep a record of plant purchases
Maintaining good records of the plant’s performance in the landscape is important - not just for the warranties, but from a maintenance standpoint. A neat way to keep all those plant tags and receipts is in a recipe file or a photo album with peel-back adhesive pages. Keep a gardener’s notebook of where and when you bought a plant, on their progress, and on maintenance you have done such as pruning or fertilizing. Take lots of pictures and keep them on record as well either in hard copy or digital form. Finally, enjoy the fruits (and flowers and foliage) of your labor. Good luck and happy landscaping!

 

 

 

With many areas of the state experiencing drought, diligent gardeners are moving sprinklers from flower bed to flower bed. Although the plants appreciate this extra moisture, so do the fungi and bacteria that cause plant diseases. The diseases now appearing in Minnesota’s gardens started as a few leaf spots several months ago and have now grown into large and quite noticeable infections.

For most of these diseases it is too late to apply a fungicide. Fungicides are protective in nature and will shield a plant from new infections. Unfortunately they are not capable of curing an existing infection. Several cultural practices can be helpful. Also remember that many garden diseases can be tolerated and will not kill the plant, although they may reduce its vigor.

• Daylily leaf streak is caused by the fungi Collecephalus hemerocalli. This disease starts out as tan or brown oval shaped spots. These spots are often surrounded by a yellow halo and grow into long brown streaks. Spores of the fungus can be blown into the garden by wind or the fungus can be introduced on infected plants. The fungus survives MN’s winter in dead leaves that were infected the previous summer. To manage daylily leaf streak, remove all dead leaves from the garden at the end of the growing season. Severely infected leaves can be removed during the growing season to reduce spread of the disease. Split dense clumps of daylilies to improve air circulation around the plants.

• Powdery mildew is easily recognized by the white powdery spots on green parts of the plant. Many different fungi from the same family cause powdery mildew on garden plants. Infections where leaves have green tissue and only a few white spots will not seriously hurt the plant and gardeners can tolerate this minor infection. If leaves are turning yellow and falling off due to powdery mildew, however, plants are severely infected and should be replaced with a disease resistant cultivar the following year (many are available).

• Bacterial leaf spot on zinnia causes brown to black spots on leaves and reddish spots on petals. These bacteria can come into the garden on infected seed and are easily spread by splashing water. It is common to see this disease on the lower leaves where humidity is high. Planting zinnias so that air moves around the plant, can help reduce problems with bacterial leaf spot.

• To provide plants with water without encouraging disease, use drip irrigation or soaker hoses whenever possible. This will provide water to the roots without wetting the leaves. If sprinklers are being used, water early in the morning so that leaves dry quickly in the sun. Avoid watering in the evening because moisture will sit on the leaves all night long providing the perfect environment for plant pathogens to grow.

 

 

 

When I gave the annual flower tours at the University of Minnesota-Morris Trial Gardens this year, I looked at what’s new with annuals. Here is a (very!) brief update:

The California Pack Trials this spring involved 30 flower breeders and propagators showing their cutting edge new introductions. With about 10 new items per propagator, this adds up to about 300 new plants for 2007!!! No wonder we cannot keep up with all the new things now seen at garden centers!

The U of M Display gardens at Morris, St. Paul and Grand Rapids may get these items a year in advance so you can see these new plants and how they perform in our growing conditions.

Pan American is putting a lot of emphasis on the new “petite flowered” Shock Wave™ petunias. Frankly, to me these look a lot like the Easy Wave® or Original Wave® already on the market. They have lots of flowers and a similar trailing plant form.

‘Baby Duck’ is a nice yellow petunia looking good at Morris and St. Paul this year, ‘Sunray’ is another nice yellow this year at Morris. Both are robust and full of flowers.

Probably many of you have had annual vinca, also known as Madagascar periwinkle (Catharanthus roseus), die from phythophthora root rot. New genetic work now gives us two disease resistant lines: the Nirvana™ and Cora™ series both have several colors. Both of these lines looked great at Morris and St. Paul, with huge flowers and attractive foliage. Some aster yellows was visible in Morris on three plants.

The verbena series Aztec™ and Lanai™ looked very good in Morris. Each comes in several colors. However the Magalena™ series verbenas were half dead (maybe from powdery mildew?) and only Magalena™ Ultra Hot Pink was acceptable in this line. That verbena Lanai™ series has looked good in Minnesota for several years.

Cleome Senorita Rosalita™ is resistant to oedema (blistering on leaves caused by excess water uptake, usually more of a problem in greenhouses than outdoor gardens). It has darker foliage and very showy lavender pink flowers. Overall the flowers are smaller than typical cleome, but are fragrant and not so large they fall over. Looks super!

Euphorbia Diamond Frost® was flowering profusely and will again win a place in the top performers as it did last year. Its open, airy form and tiny white flower bracts make it a great filler in containers. This plant is in short supply as even growers are complaining that they cannot get it to grow and sell. Sounds like everyone loves this if they can find it.

The dark, almost totally black foliage of Dahlia ‘Mystic Illusion’ is a contrast to its bright yellow flowers. Grown from cuttings, this probably produces a tuber you can store and save from year to year. Along with Pennisetum ‘Purple Majesty’ and ‘Jester’, and Capsicum ‘Black Pearl’, you can almost have a black annual garden now.

Totally new annuals (for me, anyway!):
Purslane Rio™ Scarlet and Rio™ Yellow: Super tough succulent like (close to their relative the weeds) but flowers were numerous and showy. The downside: flowers totally closed up at about 5:30 pm when the sun went down. Also closing up for the night were Anagallis Angie™ Orange and Angie™ Blue. These low growing flowers were showy, but until the breeders prevent the flowers from closing these will probably not become too popular.

Talinum paniculatum ‘Limon’ looks like plastic with its chartreuse foliage and airy pink-red flowers. Heat and drought tolerant and looks very tough. Most of us know plectranthus, but how about Plectranthus ‘Cerveza ‘n Lime’ ? It looks like plastic also, so much so I touched it. Nice mound with attractive scalloped leaves.

Cool new annuals are out there!! Take a pencil and paper with you to the trial gardens, the names are ones you will want to write down to remember for next spring when you go to the garden center.

 

 

 

If you are looking at hackberry, white or bur oak, juneberry (serviceberry), hawthorn, chokecherry, basswood, cotoneaster, walnut, or other trees and shrubs and notice that the upper surface of the leaves have a speckled yellowish or whitish discoloration, turn one of the leaves over. Chances are you will discover an infestation of lace bugs.

Lace bugs are very small, flat insects, about 1/8th inch long and light-colored with black markings. What distinguishes these insects (if you have enough magnification or really good eyesight) is the lacy or sculptured appearance to their wings and the area around their head. Immature lace bugs are smaller and spiny. Don’t be surprised to see black specks on the underside of the infested leaves which are their droppings.

Lace bugs feed on plant sap using their piercing, sucking mouthparts. Although trees and shrubs may not look great due to the discoloration, most infestations do not cause significant damage to woody plants as long as they are well-established and healthy. In most cases it is not necessary to treat lace bug infestations. However, if your plants are under stress or have been severely attacked by lace bugs or other pests over the last several years, you may wish to treat them to protect the health of your trees and shrubs. Most residual tree and shrub insecticides, such as bifenthrin, permethrin, or cyfluthrin will be effective.

Bonus Entomology Tip!
Yellowjackets, picnic beetles, and multicolored Asian lady beetles can be common in gardens, attacking various fruits and vegetables. In nearly all cases, they are first attracted to overripe or damaged crops. Sanitation is the best management: harvest fruits and vegetables as they ripen and pick up and dispose of any that are laying on the ground. Insecticides are of minimal value.

 

 

Minnesota roadsides, prairies, and gardens shine in mid to late summer with the glorious, brightly-colored yellow, gold, and mahogany blooms of Rudbeckia hirta (common names include black-eyed Susan, gloriosa daisy, and hairy coneflower). Besides R. hirta, common coneflowers (plants with flower heads having an elevated center of disk florets) include purple cone flower (Echinacea spp.) and upright prairie coneflower (Ratibida columnifera). Black-eyed Susan is the common name for many members of the genus Rudbeckia and comes from that fact that most individuals have a chocolate-brown center cone of disk florets. Of all the coneflowers, R. hirta is the most common and widely naturalized.

Rudbeckia hirta is native or naturalized throughout most of the continental United States and thrives in typical, full sun garden settings. It is well-adapted to relatively poor soils and is typically not bothered by pests except for occasional bouts with powdery mildew. The abundant hairs covering the stems and foliage of R. hirta give it a unique appearance and has inspired the common name, hairy coneflower. These hairs provide protection by deterring insects and other herbivores (plant eaters). Rudbeckia hirta provides color over multiple weeks and is a long-lasting cut flower. The cultivated strains of R. hirta (often called gloriosa daisies) typically have larger, more double, or more richly colored petals than the straight species. Most native populations have flower heads with a single row of yellow petals or ray florets.

Under favorable conditions Rudbeckia hirta is a short-lived perennial, but often acts as an annual or biennial in Minnesota gardens or prairies. Moisture is a critical factor influencing the ability of plants to survive winter. Survival is favored when plants are grown in well-draining soil, as is the case for other perennials that don’t tolerate wet winter soils such as English lavender and coral bells. In order to encourage a persistent population of R. hirta, plant them in locations where they can freely reseed and replenish in number. They can also be grown as an annual.

Flowering and stem elongation of R. hirta is highly sensitive to daylength. Rudbeckia hirta is classified as a long day plant. Under long day conditions (greater than 12 hours of light; perceived by the plant as less than 12 hours of continuous darkness) stems elongate and flowers are initiated (Murneek, 1940). Short days inhibit stem elongation and flower initiation. Under short days (nights longer than 12 hours), seedlings produce a flattened rosette of foliage with leaves oriented horizontally. After day length reaches more than 12 hours (continuous darkness of less than 12 hours), leaf orientation changes with leaves becoming more vertically oriented. Internodes (stem between leaves) elongate and flower buds initiate in the growing points. Under long days plants will continue to grow in height and flowers develop normally. If a plant that has been grown under long days is returned to short days, stems will cease elongating. Once flowers are initiated under long days, they typically continue to develop under short days.

Seedlings of R. hirta can be started indoors in the spring with other bedding plants and transplanted outdoors. If started early, direct-sown seeds can flower the same season as well. Late season seedlings form rosettes of foliage under short days and will flower the following summer if they overwinter. With an ever increasing selection of cultivars that differ in characteristics such as plant height and floral traits, R. hirta can make a great addition to almost every sunny garden.

Here is a list of some of the most popular cultivars:

‘Becky’- Very compact (about 10 inches tall), well-branched plants have relatively large flowers. Blooms are single and come in a mixture of golds, yellows, and bicolors. This cultivar has a reputation for being more mildew susceptible than others.

‘Cherokee Sunset’- Plants grow 2 to 3 ft. in height; flowers are a variable mix of semi-double to double blooms in shades and mixtures of yellow, gold, and mahogany. 2002 All-America Selection Winner

‘Chim Chiminee’- Dramatic quilled petals (shape is a long, narrow tube) come in a variable color mix on plants 24 to 30 inches tall.

‘Goldilocks’- This variety is an old-time favorite with double, golden yellow flowers with plants growing to about 2 ft. in height. This cultivar has a reputation for being more mildew susceptible than others.

‘Green Eyes’- also known as 'Irish Eyes.' This black-eyed Susan has a green eye rather than the traditional chocolate-brown. It has a single row of golden petals. Plants grow to about 30 inches tall.

‘Indian Summer’- This spectacular 1995 All-America Selection winner has very large single golden yellow blooms with wide petals. Plants are vigorous and reliable and have become a staple not only for gardeners but also cut flower producers.

‘Prairie Sun’- Similar in flower size to ‘Indian Summer’, this cultivar has rich golden-yellow petal bases and lemon-yellow petal edges with a green disk. Plants are similar to or slightly shorter in height than ‘Indian Summer’. 2003 All-America Selection Winner

‘Radiance’- This recent cultivar has dramatically quilled, golden petals. Well branched plants grow 24 to 30 inches tall.

‘Toto’- Compact, well-branched plants grow to about 10 inches tall with classic single yellow blooms and a dark brown cone.

Reference:
Murneek, A.E., 1940, Length of day and temperature effects in Rudbeckia. Botanical Gazette 102:269-279.

 

 

While drought conditions still exist over much of the state, some areas have received rainfall over the last couple of weeks. That rainfall may be enough to stimulate regrowth of our lawn grasses that may have been dormant or simply not growing very much over the last couple of months. Even though the grass foliage may still be brown, new growth can be detected by carefully looking at the base of the grass plant. New growth will be evidenced by the presence of tiny new whitish green grass blades. Some are so small that they will just barely have some green color on them. Small, whitish colored “buds” may also be extending laterally from the base of the plant. This is evidence of new lateral stem growth, such as rhizomes, stolons and tillers. New whitish colored roots may also be starting to form and extending down into the soil. With the new growth beginning and somewhat cooler temperatures returning, keeping the lawn watered and even supplying about ½ pound of nitrogen per 1000 square feet around the middle of August will help restore turfgrass vigor and encourage continued regrowth and recovery. Since late summer and fall periods are naturally active periods of turfgrass growth it is desirable to encourage healthy growth during this time. Maintaining healthy, green growth throughout this period will better prepare the plants to survive our winter conditions and perk up more quickly next spring.

Unfortunately, we are also starting to see evidence of those lawn and turfgrass areas that failed to survive this summer’s hot and dry conditions.  When examining those areas, the whole grass plant will be brown and dry with often a dark brown color near the base of the plant.The shoot area near the base of the plant will be soft and dry as opposed to a firmer, whitish green color indicating that the plant is likely still alive but perhaps not actively growing.&Also, there will be no evidence of new grass blade growth or new root or lateral growth. Where these conditions are present, some form of lawn renovation and/or overseeding will be needed.  The last half of August through the middle of September is an excellent time for lawn renovation and reseeding to be done.  For a complete discussion about the process of renovation, see the Extension Factsheet entitled Lawn Renovation. Successful lawn renovation is also discussed in the University of Minnesota’s Sustainable Urban Landscape Information Series website at: http://www.sustland.umn.edu/maint/maint.htm. In the latter site, scroll down the “chapters” pertaining to lawn care until you reach Chapter 6, “Renovating an Existing Lawn for Sustainability.” Click on this to get to the information.

 

 

If you’re looking for a fun addition to your late summer garden consider some naked ladies. Nope, these naked ladies won’t get you in trouble with your neighbors or the law. We’re talking about a summer blooming bulb, Lycoris squamigera, which has many common names including magic lily, surprise lily, resurrection lily, and that attention-grabbing one - naked ladies.

All of these names refer to this bulb’s curious growth cycle.  In spring, long, straplike leaves emerge from the bulb.  The foliage does its photosynthesis work, then dies back and disappears by mid-summer. Then the surprise occurs: In August, 2 to 3 foot tall flower stalks rapidly arise, topped with lovely pale lilac-pink flowers. 

Though often listed as Zone 5 hardy, many Zone 4 gardeners successfully grow this bulb. A layer of winter mulch provides extra protection. Plant in full sun or partial shade in average soils. Magic lilies add a nice bit of color and unusual form to late summer gardens.

 

 

Garlic Lovers Unite!
2nd Annual Minnesota Garlic Festival
Saturday, August 18
Wright County Fairgrounds in Howard Lake, 10 a.m. to 8 p.m.
Visit the official festival website:
http://www.sfa-mn.org/garlicfest/index.html

For larger views of most images, just click on the image.

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Happy gardening!

Nancy Rose
Editor
Regional Extension Educator - Horticulture

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