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Petaloids are common in many of the flowers we grow and give us the impression of additional petals for fuller, “double” blooms. There are four main organs that comprise flowers- sepals (green leaf like structures that surround and protect developing flower buds), petals, male and female organs. Petaloids are stamens and even sometimes pistils that appear petal-like and result from a disrupted transition between petal tissue and stamens. The degree that a petaloid can resemble a true petal varies based on species, cultivar, and particular environmental conditions. Petaloids are making the flower look fuller is the case of clematis ‘Multi-blue’ compared to a more typical clematis cultivar (inset photo- clematis ‘Contessa de Bouchard’). Even after the true petals fall, petaloids of ‘Multi-blue’ continue to provide color and additional ornamental interest. Other familiar flowers with some cultivars containing petaloids leading to fuller-looking, double flowers include lilies, petunias, roses, and tulips.
David C. Zlesak
Spring Fever is setting in. Gardeners probably suffer from this affliction more than anybody. We are very aware of the longer days and the melting snow. Plant and seed catalogs are dog-eared sitting on the coffee table, with Post-It® notes and underlining highlighting what we ordered or desired. A walk through the garden center screams spring as we see seed displays and the supplies for seed sowing. Fluorescent lights for seedlings are being hung in basements on shelves built for this time of year. All of these are immanent signs of spring and the coming gardening season. But how do plants know when it’s spring?
First, we need to reflect back on winter and consider why dormancy occurs. The growing parts of plants (buds and seeds) are considered ‘dormant’ when they do not grow, even with proper water, light and reasonable temperatures. This feature is especially important to plants that live in climates that get especially cold (sound familiar?). If plants did not go dormant in the winter, they would probably die due to freezing or desiccation (drying out). In dormant tissues, some barrier to growth must first be eliminated before growth can resume in a favorable growing environment. Paradoxically, it is crucial to survival of the seed that the barrier to growth be robust.
‘Silver Drift’ crabapple in full flower. The Dow Gardens Archive, forestryimages.org Imagine you’re a dormant crabapple blossom. A few warm days in January might lead you to believe spring has come, so you burst forth in all your pink-petalled glory. But then comes February. Surprise! You’ve just frozen to death! Or imagine you’re a cherry pit. Wouldn’t it be nice if, rather than falling from the tree and germinating there, under the shade of your mother, competing with her for water, light, and nutrients — if you could wait to germinate until a bird came along, ate you, and delivered you to a new place where you don’t have to compete with your mother or siblings? Barriers to germination and growth are essential for growing at the right time and in a good place. Almond and peach trees are grown commercially where sufficient cold requirements are met for winter, but early spring is warm enough so growth is not endangered by frost.
In seeds, the factor(s) controlling dormancy may or may not be within the embryo. Examples of dormancy factors include a water-impervious seed coat that prevents proper hydration until sufficient degradation (morning glory), a tough walnut shell that can’t be cracked by the growing embryo, and chemical inhibitors inside the seed that must be washed away by rain in some desert plants.
Most temperate plants have a chilling requirement that serves to release dormancy before growth can resume. Like Minnesotans, they thrive in the spring and summer only when sufficiently chilled by cold winter temperatures. Typically, chilling requirements are satisfied by the accumulation of hours at cold, but not freezing, temperatures (~34–45 ºF). What happens during this phase seems to still be a mystery, but it’s usually assumed that degradation of abscisic acid, a hormone associated with dormancy, is increased in this range of temperatures. Therefore, chilling eliminates the hormonal barrier to growth that builds up in the fall. In addition, chilling temperatures are also thought to help increase the concentration of a growth promoting hormone, gibberellic acid. In woody shrubs and trees, come spring warming soil temperatures allow for food stored in the roots to travel to support the growing buds. So generally, what we think happens is that cold temperatures change hormonal barriers in the buds, then warmer temperatures allow for spring growth.
In addition to temperature, plants also respond to light. While the amount and quality of light do affect some plant growth parameters, the length of the day (or more importantly since it is what is recognized by the plant, the length of the night) has a major influence on regulating the growth and flowering for some plant species. Why would this type of adaptation be helpful for a plant? As noted earlier there can be drastic, yet ephemeral or short term, changes in weather. Living in Minnesota, I’m sure we are all well aware of the peculiar weather habits of this area. By responding to the length of the day, plants ensure that they enter the correct developmental process at the right time of the year, unaffected by “un-seasonal” temperatures. Flowering in response to the length of the day ensures that different populations of the same species all bloom at the same time, increasing the chances for cross-pollination. Cross pollination increases the genetic diversity of populations which, in turn, allows for populations that may be more adaptable to changing environments. A photoperiodic response may also ensure that seed development occurs at a time favorable for seedling development and maturation. The short days of spring hasten flowering of azaleas and rhododendrons (Rhododendron spp.), while other species such as bellflowers (Campanula spp.) bloom as the days in the spring get longer. In addition, vegetables such as spinach and lettuce (Spinacea oleraceae and Latuca spp., respectively) flower in response the lengthening days.
How are plants able to measure the length of the day? Just as we pay attention to the clocks on our walls, wrists, and ovens, plants utilize a clock as well. Plants exhibit a phenomenon in their daily cycles, called circadian rhythms (Latin; circa, “approximately,” and dies, “a day”). In a cycle of 24 hours, a plant has certain genes that are expressed in either light or dark. These genes provide feedback to each other and “set” the clock of the plant to match the light and dark periods of the day. Plants can sense light with a molecule called phytochrome that varies between two forms based on the type of light that has been encountered. These proteins are activated by exposure to red light (which is found in full sun) and promote many processes such as flowering. At dusk, the high amount of far-red light present relative to red light deactivates the proteins. These are two major ways by which the plant is able to measure the day length and perceive light.
Though some of the information presented here may be a bit technical and warrant further research by scientists, it highlights the intricacies of how plants function in response to their environment. The process of dormancy coupled with subsequent growth and development is the result of plants perceiving temperature, light and other environmental stimuli and responding appropriately. It is the orchestration of these processes that lead to a wonderful spring!
As spring approaches, it is time to think about your vegetable garden and the watering and weeding that goes into producing a bountiful harvest. Most gardeners use mulch to inhibit weed growth and retain soil moisture. The home gardener has several options to consider for the vegetable garden. These include organic mulches, such as straw and newspaper, and inorganic mulches, such as plastic mulch film.
Plastic mulch film has been used successfully for several decades in commercial vegetable production to conserve water, inhibit weed growth, extend the growing season, and increase yield. Plastic mulch is essentially a thin polyethylene film that is impermeable to water and applied over the soil surface surrounding vegetable plants. Although initially only available in black and clear forms, colored mulches are now available in a variety of colors including white, red, blue, olive green, and reflective aluminum. Plastic film mulches have the ability to reflect, absorb, and transmit light. Some colored mulches formulated with special coatings are sold as SRM (Selective Reflective Mulch) or IRT (Infra-red transmitting), meaning that the mulch reflects or transmits specific wavelengths of light. In the case of IRT mulches, only infra-red wavelengths are transmitted through the mulch into the soil resulting in elevated soil temperatures without promoting weed growth under the mulch.
Colored mulches are important in altering the microclimate during vegetable production as they change the quality of light that is reflected onto the vegetable plant. Previous research has shown that the color of the mulch used can influence yield and quality of vegetables. The most widely used result of colored plastic mulch research is the use of red plastic mulch to increase tomato yields. Light reflected from red mulch can increase tomato yields between 10-30% based on previous experiments. Other research has shown that flavor and health components of vegetables can be altered by growth on colored mulches. For instance, flavor compounds can be increased in basil using yellow colored mulch, chemopreventive compounds can be elevated in turnips with blue mulch, and B-carotene content can be enhanced in carrots using white mulch. Yellow mulch has been used with trap crops as it attracts some insects, while aluminum reflective mulch has been used to ward off insects. Trap crops are strategically placed crops used to deter or "trap" pests in order to protect more desirable or valuable crops. Black and clear mulches are used to elevate soil temperature, especially during early season growth. Current research at the Southern Research and Outreach Center in Waseca, MN is looking at the additional health benefits that can be obtained in the cabbage family of vegetables and garlic by growing them on various colored plastic mulches.
Table 1. Colored plastic mulches and their benefits in the vegetable garden.
(Source: Penn State Center for Plasticulture)
| Mulch Color | Benefits | Best crops |
| Black | Increase soil temperature | Potato, onion |
| Blue | Increase soil temperature, change light quality | Cucumber, summer squash, cantaloupe |
| Red | Increase soil temperature, change light quality | Eggplant, tomato, onion, potato |
| Yellow | Attracts insects | Basil |
| White | Decrease soil temperature | |
| Aluminum Reflective | Decrease soil temperature, deters insects | Pepper, onion and potato |
| Clear | Highest soil warming capacity |
Note: Although all colors are available at commercial volumes (usually rolls 5’X1000’) color availability in smaller lengths (3’X 50’) is limited to red, black and clear.
Using plastic mulches in the home garden.
Gardeners can obtain similar benefits from colored mulches found by commercial growers by following some basic principles. To obtain the greatest benefits from plastic mulches, it is important to start with a smooth seedbed. The greatest soil warming benefits come from mulches when they are in close contact with the soil surface. Rolls of colored plastic mulch can be purchased at many garden centers or from gardening mail order catalogs. Lay mulch tightly over soil surface by securing or burying the sides and ends of the plastic. One way to accomplish this is to install the mulch during the warmest part of the day. If the mulch is installed during this time it will be even tighter once temperatures cool. Cut slits or holes in plastic for transplanting or seeding. Mulches are most effective when they are used in conjunction with raised or mounded beds and trickle irrigation or soaker hoses are placed under the mulch. As plastic mulches retain moisture, they may not be suitable for poor draining soil types.
Interested gardeners may wish to explore the benefits obtained from specific colors of plastic mulch (See Table). For instance, black and clear mulches are good for warming the soil and promoting early season growth. Although clear plastic does provide the greatest soil warmth, it does not inhibit weeds as does black mulch. Home gardeners may also wish to use red mulch for increasing tomato yields. To obtain the maximum benefit of red mulch, tomato plants must be staked or trellised so that incoming sunlight can reach mulch and be reflected onto the plant. Remember that the colored mulches provide benefit by reflecting light back to the plant. If tomatoes are not staked and allowed to sprawl and cover the mulch, then the benefits from reflected light off the mulch will be reduced.
Strawberry plants in Woolch, 6 weeks after planting. Emily HooverResearch into the use of wool mulch (called Woolch) for the sustainable production of strawberries began at the University of Minnesota in 1998. This wool is a value added product of the Minnesota Lamb and Wool Industry, and is comprised mainly of scrap wool fibers from Faribault Mills. The other component is wood shavings. Preliminary work using Woolch demonstrated that water and nutrients can move through it, strawberry runners can root through it, but weed seeds can not grow up through it. Since then numerous trials have proven the system extremely effective in reducing chemical inputs and virtually eliminating manual weeding.
If you are interested in planting strawberries using Woolch, we would recommend the following:
Plant dormant strawberry transplants on semi-raised beds through slits in wide strips of Woolch that were laid over the beds. Allow the strawberry runners to root through the Woolch. Remove flowers as they open. In early November apply straw mulch, as on traditional plantings of strawberries. In April, rake the straw mulch into the aisles of the strawberry rows. Harvest begins in early to mid-June. During the entire process no herbicides are applied, and the wool prevents the need for fungicide application as well. Monitor for tarnished plant bug (More info...) to prevent button berry. For more information on our research and to view images of strawberries grown with Woolch, visit http://fruit.coafes.umn.edu and click on strawberry research.
We also think Woolch would be useful in home gardens to eliminate weed seed germination and retain water for plant growth. We recommend using it similarly as described above for strawberries. Prepare the soil as recommended before planting annuals (flowers or vegetables). Lay Woolch over the soil. Slit the Woolch and plant the transplants. Bury the edges of the Woolch so the mulch is in contact with the soil. Using a hose or sprinkler, water to wet the mulch so it adheres to the soil.
Woolch has an expected longevity of about two growing seasons. It will eventually decompose and can be tilled into the soil. Alternatively, a layer of new Woolch can be laid over an old layer.
For more information on Woolch, visit the Minnesota Lamb and Wool Producers web site at http://www.mlwp.org/woolch.htm.
Black spot can lead to severe plant defoliation and lead to fewer flowers and a greater likelihood of winter injury. Michelle Grabowski
Black spot lesions typically have feathery margins and can lead to leaflet yellowing before leaflets fall. Michelle Grabowski
Roses improve any garden with a flourish of color and their sweetly perfumed blossoms. Although gardeners love roses, many are frustrated by the challenge of keeping these beautiful plants healthy. Black Spot of rose, a common fungal disease of roses caused by Diplocarpon rosae, plagues Minnesota roses every year. This disease can easily be recognized by the black spots with fringed or feathered margins that form on leaves. Leaves infected with black spot turn yellow and fall from the plant prematurely. This loss of leaves results in reduced vigor of the rose plant. Often heavily infected plants produce fewer flowers and are more susceptible to winter injury. The black spot fungus produces new fungal spores within existing leaf spots throughout the growing season. These spores are splashed on to new leaves creating new infections. Within a few weeks, these new infections have become full-grown leaf spots producing additional fungal spores. This devastating cycle continues throughout the growing season, often resulting in seriously diseased roses by the end of the summer.
University of Minnesota scientists empathized with the plight of MN gardeners and their struggling rose plants. Drs. Jeff Gilman and David Zlesak, along with extension educator Michelle Grabowski decided to try out various biological control agents, low impact fungicides, and home remedies to come up with the best strategy for managing black spot. To do this, they set up two experiments at the UMN TRE (teaching research and education) nursery on the St. Paul campus. They used the rose cultivar 'Morden Centennial', which is susceptible to black spot, and maintained the plants under very moist conditions, which favors the fungal pathogen. The roses were divided into groups of 7 or 8. Each group was sprayed with one of the fungicidal treatments throughout the growing season. One group was left untreated or sprayed with water for comparison purposes. Once black spot showed up, the research scientists measured the progress of disease within each treatment.
Products Examined:
Biological Controls
Rhapsody biofungicide – This is a biological control product containing the naturally occurring bacteria, Bacillus subtilis. It is sold to gardeners under the name Serenade Garden Defense.
Sonata® biofungicide – This is a biological control product containing the naturally occurring bacteria, Bacillus pumilis.
Low Impact Fungicide
Concern Garden Defense – This is botanical oil from the Neem tree (Neem oil) sold in a ready to use spray bottle.
Sulfur spray – This is a low impact fungicide sold under many names. The spray used in the trial was Garden fungicide II by Safer® and is 0.4% sulfur
Horticultural Oil - Many horticultural oils are believed to have some fungicidal properties. The product used in this experiment was Sun Spray Ultra-Fine Year Round Pesticidal Oil plus 12.5 microliters plain Ivory® dishsoap per pint of water.
Fungicide
Chlorothalonil – This is a common garden fungicide sold under many different names.
Copper – A common garden fungicide sold under many different names. The spray used in the trial was from Bonide® and is 7% copper sulfate.
Home Remedy
Dishsoap - 12.5 microliters of plain Ivory® dishsoap added to a pint of water.
Milk - 2 parts distilled water, 1 part whole milk plus 12.5 microliters plain Ivory® dishsoap per pint.
Aspirin -Two 325mg tablets ground with mortar and pestle, mixed with 1 pint distilled water plus 12.5 microliters plain Ivory® dishsoap.
Cornell Mix – A mixture of 1 tablespoon baking soda, 1 tablespoon Sun Spray Horticultural Oil plus 2 drops Ivory® dishsoap per gallon of water.
***All commercial products were mixed and applied according to the instructions on the fungicide label. Sprays were repeated every 7 days throughout the experiment.***
Representative plants of the A) control, B) copper, C) milk, and D) chlorothanonil treatments seven weeks after contracting blackspot. David Zlesak Of the variety of products tested in this experiment, very few of them gave satisfactory control of black spot on rose. Chlorothalonil and Copper, both common garden fungicides, significantly reduced disease problems on roses compared to untreated plants. The milk treatment also successfully reduced problems with black spot on rose. Neem oil did not reduce the number of leaf spots seen on rose plants but it did reduce the amount of leaf loss that infected plants experienced. All other sprays, including the biological control products and the remaining low impact fungicides and home remedies, did not control black spot. The disease on these plants was as severe as it was on plants that received no treatment at all.
Hopefully the information learned from these experiments will help Minnesota gardeners better manage black spot on rose in the season to come. University of Minnesota scientists will continue to investigate new products, especially within the low-impact and biofungicide categories, for their effectiveness against black spot on rose.
Sweet peas are cool season crops that can be directly sown in the garden in April. David Zlesak
After the soil thaws and temperatures begin to warm in mid to late April, one can begin to plant cool season crops. Sweet peas, peas, turnips, lettuce, and spinach can be directly sown in the garden and other plants such as pansies, kohlrabi, cabbage, snapdragons, and stocks can be planted as transplants. If the temperatures fall below the high 20's°F, consider covering to insulate young plants.
Assess pruning needs of deciduous shrubs in the spring and prune accordingly. Pruning is typically best done early in the month just as shrubs start to grow to minimize stress to shrubs and so you know what tissue is alive and dead. Remove dead branches, thin out overcrowded, rubbing branches to open the center of the plant for better air circulation, and head back overly long branches to produce a more symmetrical, balanced plant. Rejuvenation pruning is a common pruning technique used on shrubs to keep them growing strongly. It involves every or every other spring removing some of the oldest canes all the way down to the base or near the base of the shrub to promote vigorous new replacement canes. Rejuvenation pruning is especially useful for lilacs and hardy roses to keep their size manageable and to help keep plants blooming strongly. Early flowering shrubs like forsythia, flowering quince, and lilacs are often pruned after flowering so as to not miss out on some of the much anticipated blooms.
Stems from last season of herbaceous perennials Rudbeckia fulgida are often more brittle and easy to remove in spring. David Zlesak
Gradually remove winter mulch from covered perennials. Old stems of herbaceous perennials from last year that may still be in place should be removed. Such stems are often more brittle in the spring than the previous fall and are easier to break off and remove. When removing old stems of herbaceous perennials in the spring, do so before new, emerging stems progress too far so they are not damaged in the process.
Many municipal compost sites reopen in April. Check with your local site for hours and the services provided. Some sites accept only non-woody plant debris, while others also accept woody brush. Many sites also provide free compost and wood chips while supplies last.
There is still time to start seeds indoors of fast-growing, warm-season annuals like tomatoes, zinnias, and marigolds for planting outside the end of May or early June.
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Happy gardening!David C. Zlesak, Ph.D.
Editor
Regional Extension Educator