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Reversion on Frosty Morn sedum. Nancy Rose
Variegated Norway maple shows many reverted, all-green sections. Nancy Rose
Contrary to what Kermit the Frog says, it IS easy being green, at least if you’re a plant. What’s difficult is being variegated.
Instead of being solid green, most variegated plants’ leaves are streaked, speckled, or edged with white, cream, or gold. Variegation is often caused by cell mutation. In nature, these leaves are at a disadvantage compared to all-green leaves, since they don’t have as much chlorophyll - the vital pigment involved in photosynthesis.
Some variegated plants are quite stable and will maintain their patterned form. Others, though, are prone to reversion. Reversion occurs when the foliage on new growth reverts to all-green, losing the variegation. All-green sections are usually more vigorous than variegated sections, so the entire plant may eventually revert to a solid green form.
Reversion is particularly common and noticeable on variegated Norway maple (Acer platanoides ‘Drummondii’). Reversion also occurs on some variegated shrubs and even perennials like the ‘Frosty Morn’ sedum shown here. Prune out all-green reversions to maintain the variegated form. -Nancy Rose
Mmmm...rhubarb pie! Hayford Peirce
When people think of management strategies for controlling diseases in the vegetable garden, the thought is rarely a pleasant one. It may mean fungicide sprays, pulling out virus infected plants before they ever produce fruit, or laborious tasks such as staking tomatoes, pulling weeds and removing all dead plant material at the end of the season.
Well, the good news is that there are two diseases that you can manage by making pie. That’s right -- going out and harvesting your rhubarb can actually reduce certain diseases. The trick is to be able to identify the disease and selectively remove the stems containing the infection.
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Rhubarb leaf spot. Michelle Grabowski
Rhubarb is attacked by several different leaf spot diseases. Two of the most common of these leaf spot diseases are caused by the fungi Ascochyta rhei and Ramularia rhei. Ascochyta leaf spots start as light green or yellow spots that eventually grow into white spots with a thick red margin. Often times the dead leaf tissue at the center of these spots falls out, resulting in shot-hole leaves. Ramularia leaf spots start as small red spots that eventually develop a white or tan center and a purple margin. Ramularia rhei can also cause infections on rhubarb stems. These infections start as small spots and grow into sunken white or tan ovals.
Spores from both pathogens are spread from existing spots to new leaves by wind or splashing water. Removing those spots from the garden will reduce the amount of fungal spores available to start new infections. Selective harvesting can therefore significantly reduce the amount of disease in the rhubarb patch. As you choose stems to harvest for your next culinary masterpiece, first select any stems that show leaf spots. The fungi can survive and produce spores on dead leaves, so the leaves must be removed from the garden in addition to the stems. The infected leaves can be buried, composted (only if the compost pile is actively managed to get hot enough to kill spores), or otherwise discarded. This will reduce the number of new infections that develop on the plant.
In addition to selective harvesting this spring, make sure to remove all leaves from the garden in the fall after they have been killed by a frost. The leaf spot fungi survive the winter on old leaf tissue. Also encourage good plant growth by planting rhubarb in full sun and providing proper fertilization. Rhubarb plants are typically fertilized as growth begins in the spring and again after the last harvest. Have garden soil tested at the U of M soil testing laboratory to determine the proper amount of fertilizer to apply.
Fall cankerworms. Jeff Hahn
It has been a great year for caterpillars so far-- great, that is, if you like caterpillars. They certainly have been very conspicuous to many people this season. Many first noticed holes in leaves and then saw the culprits when they looked more closely at their trees. Depending on where you live you may have encountered one or more of the following spring-time caterpillars.
Cankerworms
A type of inchworm, these caterpillars are smooth, slender insects about one inch long when fully grown. There are two very similar looking species, the spring and fall cankerworm. You can distinguish between them by examining the fleshy prolegs on the abdomen; spring cankerworms have two pairs while fall cankerworms possess three pairs. They are variable in color ranging from a light or yellow green to brownish to black in color. Spring cankerworms have a whitish or yellowish stripe running along the side of their body.
Cankerworms are found on many deciduous trees, especially elm, linden, basswood, oak, ash, apple, maple, walnut, hackberry, and boxelder. It is not unusual to see cankerworms hanging suspended from a silken thread. When the wind catches them, they can be transported to adjacent trees. When they first start feeding, they chew small holes between the major veins, making it look lacey. As they continue to feed, they enlarge the damaged areas until all that remains are the big veins.
When American elms were very common (before the devastation of Dutch elm disease), cankerworms would go through cycles of very high populations lasting for 2 to 7 years followed by periods of very low populations for 13 to 17 years. We have not seen high numbers of cankerworms since the 1980s. Is this the beginning of a new cycle that has just taken some time to gather steam or is this just a small blip that will even out shortly? Time will tell.
Forest tent caterpillars. Jeff Hahn
Forest tent caterpillars
Also known as armyworms, forest tent caterpillars are familiar insects periodically in the north and central areas of Minnesota. These caterpillars are blue and black with distinctive footprint or keyhole shaped white spots on their backs. They are mostly smooth except for hairs that stick out along the sides of their body. Maturing at two inches long, forest tent caterpillars feed on many deciduous trees, including aspen, birch, maple, crabapple, apple, ash, oak, and elm.
They go through cycles of tremendously large numbers, lasting 5 to 8 years, before collapsing to such low numbers that they are barely noticed. Low population periods typically lasts 8 to 13 years. Despite their name, they do not make conspicuous webs on trees, although they are quite capable of making silken lines which helps them to move about. As a pest in northern and central Minnesota, forest tent caterpillars peaked in 2002 and their numbers have crashed to the point where they are seen in very few places. The Minnesota DNR reported that there still remains fairly large populations in northeastern Stearns and northeastern Grant counties. Large populations have also been reported in Otter Tail county.
We occasionally see forest tent caterpillars in the Minneapolis-St. Paul area but generally not anything that is too noticeable. However this year, there have been many sites in Minneapolis and St. Paul and the surrounding metro area where they have been quite common. If you don’t notice them feeding, you will see them when they crawl down in mass to look for places to pupate. It will be interesting to see whether these populations will be cyclical like they are in northern Minnesota or whether they will maintain more stable numbers in southern Minnesota.
Eastern tent caterpillars. Jeff Hahn
Eastern tent caterpillars
These are easy insects to identify -- just look for the webbing they make in the forks of tree branches. Look for them on hardwood trees, particularly fruit trees, like apple, chokecherry, crabapple, plum, and cherry. These caterpillars are two inches when fully grown and are bluish black with yellow and a continuous white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. Eastern tent caterpillars are common most years, including this year, although they are technically considered to be cyclical like forest tent caterpillars.
An easy non-chemical method to manage eastern tent caterpillars is to wait until evening when the caterpillars have returned to their webbing, then pull it out along with the caterpillars. Then destroy the insects by bagging, burning, or burying them.
Other Caterpillars
There are other common caterpillars that may be seen but have not necessarily been reported as particularly common this year. These include whitemarked tussock moths, spiny elm caterpillars, and linden loopers.
Bonus Track - European pine sawflies
European pine sawflies. Jeff Hahn
Like some music CDs that offer extra music tracks on their albums, here’s an extra bonus insect for you. European pine sawflies have also been very common in many places in Minnesota this spring. Although they look like little caterpillars, they grow up to be non-stinging wasps. Growing between 3/4 to one inch long, these larvae have black heads with greenish gray bodies and dark green stripes. You can distinguish between sawflies and caterpillars as sawflies have 6 to 10 pairs of prolegs (fleshy legs on the abdomen) while caterpillars have 2 to 5 pairs. European pine sawflies feed on the old growth of pine, especially mugo pine. They are gregarious and it is common to find many of them clumped together as they feed.
Management
The decision to treat these caterpillars (and sawflies) should be made based on several criteria. The first factor to consider is the amount of foliage that has been consumed. In most cases there are only a few branches that are affected and the tree can easily tolerate the damage. Leaf feeding tends to be more a cosmetic problem and not one that threatens the health of the tree. Even if defoliation is severe, healthy, well-established trees can withstand this feeding in a given year. However, young trees are less tolerant and should be protected. Unhealthy, stressed trees should also be protected from severe defoliation.
Another important consideration is the size of the insect. Ideally these insects should be treated when they are 1/2 their full-grown size or smaller. The larger they are, the closer they are to being done feeding. By the time most people read this, it will be too late to treat most spring caterpillars as they will already be at or approaching their full grown size. If you have missed the window for treatment and you have at risk trees, be sure to monitor your trees in early spring next year and treat when the larvae first hatch.
There are a variety of residual insecticides that you can use if it is desirable to protect your trees. Consider using products that have a low impact on the environment, such as Bacillus thuringiensis, spinosad, and insecticidal soap. Bacillus thuringiensis is a particularly good product if the tree is flowering since it will not harm visiting honey bees. However, Bacillus thuringiensis is not effective against sawflies.
With such great weather upon us, it’s a hard thing to avoid digging right into a landscape project. However, before you dig in there are some things you should do that will save time, money, and help you safely create a great landscape that will be sustainable for years to come.
Call (800) 252-1166 before you dig.
Tip #1: Mark utilities and irrigation lines.
Save yourself from broken water lines, cut phone lines and (worse) electrocution by contacting GOPHER-1 and having them mark the utilities on your property. You can also access the Gopher State One website and click on the red “Attention Homeowners!” box to file their Gopher State One Call locate requests. This is a FREE service.
Likewise, contact your irrigation company and have them also mark your irrigation lines. While not as dangerous as a cut electrical line, you will still save the cost and delay of repairing a line broken by a spade or a tiller.
Tip #2: Test your soil.
Spend the time preparing your soil properly before starting any project. The University of Minnesota Soil Test Laboratory will test your soil for a small fee and provide a wealth of information including what you have in your soil and what your soil is lacking. Access information on how to submit a soil test by visiting the University of Minnesota Soil Testing Laboratory.
A plot plan.
Tip #3: Get hold of the lot plan or plot plan for your property.
This will give you a base plan to work from when laying out your new landscape. According to SULIS, the Sustainable Urban Landscape Information Series website (http://www.sustland.umn.edu), a lot plan is a plan developed to scale showing property lines, bearings and distance, true North, easements, setbacks, right-of-ways, sidewalks, streets and boulevards. The plot plan shows the lot with the structures accurately located on it. Plot plan information is usually available from the developer, or the city or county offices. Completed plot plans can be obtained for most new developments from architects or your county or city offices. You may need to hire a surveyor to accurately identify this information on older properties.
You can also access overview images of your property via Google Earth, Google Maps or Maps Microsoft. Google Earth can be downloaded for free from http://www.googleearth.com. Maps Microsoft can be accessed via http://maps.live.com. Reminder: You need to have a live internet connection when accessing any of these websites and they may function more slowly if you are on a dial-up connection. (Note: These sites can be addictive!)
Accurate measurements are essential for successful landscape projects. Julie Weisenhorn
Tip #4: Use the SULIS Client Interview and Site Survey Form
These sites will get you started thinking about your landscape. Use them as a basis for opening up conversations with the people in the household who will be using the landscape (see Tip #5). According to SULIS, there are five considerations for a sustainable landscape: functionality, maintainability, environmental impact, cost effectiveness, and the aesthetic quality (more info). By thinking and talking about these five key points and how they relate to your site, you will have a landscape that fits your needs and desires, and is sustainable.
Tip #5: Talk about your landscape.
Involve the people who will be using the landscape in the planning process – your spouse, your partner, your kids, extended family living with you, renters. Talk about play areas, pet areas, vegetable gardens, perennial gardens, views, shade and sun.
Tip #6: Investigate zoning laws and apply for permits BEFORE you start a project.
This is especially important if you are planning to add a deck, a patio, steps, a fence, etc. The SULIS website has a great report for Twin Cities area homeowners entitled Zoning and Permits: What You Need to Know as a Designer. While you may need to find additional information, this report will get you started.
Careful landscape planning leads to beautiful results. Julie Weisenhorn
Tip #7: Decide how much you want to spend on your landscape project.
... and then add a little more. Likewise, figure out how much you want to spend on your landscape in the future – you’ll probably want to add more plants, and you’ll need to replenish and apply such things as fertilizer, mulch, soil amendments, etc. as the landscape ages.
Tip #8: Decide what you like and want to keep in your landscape.
Tag or mark with a stake your “keeper plants” and be sure to locate them on your plan. If you have to move perennials temporarily, take a picture of your current garden so you can remember how it was arranged. In fact, be sure take before and after pictures of your project!
Tip #9: Be accurate when you locate existing trees, shrubs, decks, patio, walks, etc. on your plan.
Take the time to measure carefully and enlist the help of a couple other people. It will make the job go much smoother. For long distances such as the side of your house or a property line, use a tape measure or a measuring wheel to get an accurate measurement. Rent a laser level for determining elevation changes or if you are making changes to the grade of your site. Draw on a copy of your lot or plot plan or sketch on graph paper. Be sure to mark where North is located and use a scale. Take your time and be as accurate as possible. Like your soil, spending the extra time up front is well worth it!
Tip #10: Talk to your neighbors about your project.
Depending on the extent of your landscape project, it may be a good idea to keep your neighbors in-the-know. Landscapes affect everyone and can create some bad feelings between neighbors. For example, if you plan to plant a tree where it will cast shade onto your neighbor’s yard, it would be a good idea to run that by them. You may find you are shading the only area in their yard where they can grow a vegetable garden!
The popularity of combining different plant materials in hanging baskets, window boxes, and containers has soared in recent years. Combining plants of various color, texture, and plant habit to design what in essence become miniature landscapes can be a very creative and rewarding endeavor. The diversity of plant materials to choose from and effects that can be generated seem almost limitless.
This container combines plants that will grow well together through the growing season. David Zlesak
A decade ago when I was a greenhouse grower at an independent nursery, designing and raising our own combination baskets and planters was one thing that helped set us apart from the competition. Combining different species or cultivars of plants that grow in harmony with each other throughout both the production period and after purchase is challenging and requires looking beyond just what looks good together at the time of planting. Much of the fun is to experiment to find combinations that work. Familiarity with the cultural needs and growth habits of different plant species and cultivars can go a long way to better choose combinations that will work well over the long run.
Group plants with similar cultural requirements.
Light
Combine plants that share similar light requirements. Plants that do well with half a day or more of full sun include salvia, marigold, petunia, and zinnia. Plants that need to be shaded most of the day include common impatiens, tuberous begonias, and fuchsia. Higher and lower light-requiring plants can sometimes be successfully combined. For example, combine larger, higher light-requiring plants that cast shade with smaller, shade-tolerant plants. Temperature preference is often closely allied with light requirement. Heat loving annuals like gazania and moss rose also prefer full sun.
Water
Combine plants with similar moisture needs. Plants that can tolerate or prefer being kept on the dry side include gazania, moss rose, verbena, and zinnia. Those that prefer to be kept on the moist side include coleus, tuberous begonias, and fuchsia.
pH
The pH of the growing medium influences nutrient availability and other aspects of plant growth. In addition to the starting pH, pH can change over time in response to water quality and type of fertilizer used. Often the pH of city water is elevated to a pH of over 7.5 with sodium hydroxide or other bases to protect metal pipes from slowly deteriorating. High water pH can elevate potting medium pH over time. The rate of pH increase is dependant on the alkalinity of the water (capacity of things dissolved in the water to neutralize acids) and pH buffering ability of the particular medium. Knowing the pH will aid in selecting better adapted plants. For instance, geraniums, celosia, and marigolds prefer a higher pH and petunia, pansy, and bacopa a lower pH.
Combine plants considering their growth and flowering traits
Overly vigorous Purple Wave petunia crowds out lamium and euphorbia. David Zlesak
Vigor
Using plants with similar growth rates helps to prevent slower growing plants from being smothered by vigorous neighboring plants. A very vigorous spreading petunia cultivar, for instance, may choke out a neighboring compact-growing ageratum or geranium. One factor that influences growth rate is response to fertilization. Many of the more expensive, specialty annuals like spreading petunias, bacopa, and sun coleus, for instance, are heavy feeders and can grow quickly in a nutrient-rich environment.
Growth habit
Some plants have looser, more open, airy growth habits and tend to intermingle and flower better with each other, while other plants have denser growth and more difficulty growing with other plants. Growth habits also vary between upright, mounding, or trailing. Loose-growing trailing verbena and bidens cultivars can intermingle and flower well together, while geraniums, tuberous begonias, spreading petunias and bacopa cultivars tend to make a thick, mounded plant or a relatively dense mat of growth. Upright, taller growing plants are often placed towards the center or back of a container, while spreading or trailing plants are placed near the edge of the container where they can grow over the containers edge. Understanding growth patterns of plants can help in determining placement in the container and how close to plant different species so each is showcased, not smothered.
Flowering time
Some plants flower continually, while others have more limited periods of bloom. For instance, osteospermums (cape or sunscape daisies), snapdragon, and pansies reduce or stop flowering during the heat of summer, but flower again once the temperatures cool down. Mixing container plants so that something is blooming at all times during the season can help extend the contribution of the container to the garden or landscape.
Plants in this hanging basket have loose, trailing growth habits that mix well. David Zlesak
Vast plant selection options
Annuals
Annual bedding plants are traditionally used for container planting since plants are typically discarded after each season and replanted in the spring. In addition to traditional annuals search out newer, compact versions of old favorites that are more amenable to confined spaces. For instance, the Sparkler series of cleome is more compact than the traditional Queen series and the new cleome cultivar Senorita™ Rosalita is not only compact, but does not have spines on the stem and does not set seed.
Perennials
Many plants used as annuals in Minnesota are actually perennials in their native climate. Examples include geraniums (Pelargonium) and fuchsias. Also consider using hardy Minnesota garden perennials in containers. At the end of the season they can be nestled into a perennial bed to extend their value, or discarded as an annual. Frequently-used perennials for containers include lamium (Lamium maculatum, L. galeobdolon - plants are low and spreading and variegated foliage looks great even when not in flower) and golden-leaved creeping Jenny or moneywort (Lysamachia nummularia ‘Aurea’). Compact versions of standard perennials that have a long flowering season make great choices as well and include astilbe ‘Sprite’, heliopsis ‘Tuscan Sun’, and scabiosa ‘Butterfly Blue’.
Woodies
Compact versions or carefully pruned specimens of an especially ornamental woody plant can make a great accent or focal point in a container. Some woody plants have especially interesting flowers, foliage, or texture. Potential options include buddleia (butterfly bush) which has a long season of summer flowering, variegated or dappled willow (Salix integra ‘Hakuro Nishiki’), and dwarf conifers.
Uncommon foliage
Foliage color, shape, texture, and size all can add unique elements to a design, even if the plant never blooms. In addition to foliage plants such as dusty miller, coleus, alternanthera, and dichondra, consider using herbs and vegetables with interesting foliage color and texture such as fennel, parsley, and rosemary. Gold, purple-black, and variegated cultivars of ornamental sweet potatoes have become very popular and are quite versatile in containers. One unique consideration with sweet potato is that in relatively small containers the tubers it produces can easily crowd out other plants as the season progresses.
Basic container garden growing recommendations
Tiger Eyes sumac combined with golden moneywort and fescue grass. David Zlesak
Choose containers (baskets, window boxes, pots) that have holes for drainage and are also a suitable size to accommodate the plants as they grow throughout the season. Often too small a container is chosen or too many plants are put in a container at planting time which leads to overcrowding problems by midsummer. Look beyond how full, colorful, and proportional the pot looks at planting time and envision the container and size of the plants a few weeks later and throughout the rest of the growing season. The larger the container the greater the space for potting medium. This is beneficial for added root development and also allows for greater reserves of moisture and nutrients, allowing extended time between waterings.
Potting media need to have a balance of both moisture retention as well as porosity so oxygen can get to the roots. If the medium does not have good aeration and frequently becomes waterlogged, then roots can be deprived of oxygen, slow in growth, and more likely rot. On the other hand, a medium that is too porous can be challenging to water frequently enough to keep moist. Most standard, suitable mixes for containers are high in organic matter (often containing peat moss, compost, and/or bark) and may contain perlite or vermiculite for added porosity.
Containers can dry out quickly, especially on hot windy days and after plant materials grow and their demand for moisture increases. To help with watering needs, leave at least half an inch from the surface of the media to the rim of the container when planting. This will provide space for water to puddle and then slowly soak in without quickly running off.
You may also see water crystals or beads (hydrogels) sold as a means to help hold moisture in potting media. Water beads are dry crystals that can absorb multiple times their weight in water. They can be hydrated and mixed into the medium before planting. Although water beads or crystals can hold water, research conducted by Dr. Jeff Gillman at the University of Minnesota suggests that they may be holding onto water too tightly and not benefiting plants because the water is not readily available to plant roots. More work is being done by Dr. Gillman using different brands and formulations this season.
Lawn Watering. Bob Mugaas
Itasca strawberry. Dave Hansen
Itasca™ is a luscious new Junebearing strawberry suitable for home gardens as well as berry farms. Itasca is a useful winter hardy, early season variety that performs well in the Midwestern and Northeastern US and in eastern Canada from USDA hardiness zone 3b to 5, based on testing in Minnesota, Iowa, Michigan and Pennsylvania.
Itasca™ ripens from early June in southern Minnesota to mid-June farther north. This puts its ripening slightly later than Annapolis and Sable but with Northeaster and before Honeoye or Cavendish. In yield trials, it has been a productive variety, producing similar quantities of berries as the varieties Annapolis and Sable. Berry size is medium-large, a bit larger than Annapolis. Itasca™ has bright red skin and the flesh is orange-red, smooth and moderately firm in texture. The flavor is moderately intense sometimes with an aroma that reminded one Minnesota grower of tangerine. The berry skin has been durable relative to other early season cultivars for the North Central US, making it easier to pick and transport without damage. It is excellent for fresh eating as well as jams and pies.
The original seedling plant of Itasca was screened for resistance to 5 common eastern US races of the pathogen causing red stele. The foliage has been highly resistant to powdery mildew and leaf scorch and moderately resistant to leaf spot.
Grow Itasca™ strawberry in moist, well-drained soil of good fertility. As with other strawberries in cold climates, apply a winter mulch of clean straw to help protect the crowns and flower buds. Strawberries are attractive plants and can be grown as a ground cover or landscape ornamental as well as for fruit production in a traditional bed.
Itasca™ strawberry plants are available at many Minnesota nurseries and garden centers and from mail order sources including Krohne Plant Farms and Nourse Farms.
It’s finally safe (maybe!) to plant warm season vegetables like tomatoes, peppers, eggplants, cucumbers, and basil outdoors in most of Minnesota. Warm season annual flowers can also be planted now.
Harvest early crops like radishes, spinach, leaf lettuce, and other early salad greens. Sow additional seeds of salad greens in small sections for ongoing harvests.
Remove flower stalks that arise from rhubarb plants.
Deadhead late tulips and daffodils but do not remove the foliage until it dies back on its own - the bulbs needs energy from the foliage in order to bloom again next year.
Roseslug sawflies are actively feeding on rose leaves. Scout for them and treat plants if needed while larvae are still small.
Anthracnose is common on a number of shade trees this time of year, especially if the weather is wet. See: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLNews-June0106.html#fungi
Four-lined plant bugs have been reported on perennials in many gardens. Look for the charactersitic areas of tiny round black dots on succulent new foliage. See: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June0199.html#bug
Spittle bugs are also active, creating foamy blobs in leaf axils of many perennials. http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June1500.html#spittle
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Back issues Yard & Garden Line News for the past nine years are online at http://www.extension.umn.edu/projects/yardandgarden/ygline-news.html.
Deb Brown will answer gardening questions as a recurring guest on the Midmorning show on MPR. 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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Happy gardening!Nancy Rose
Editor
Regional Extension Educator - Horticulture
Home « Gardening News « June 1, 2007