|Yard & Garden Line News
Volume 5 Number 1 January 1, 2003
Understanding Flower Fragrance
Charlie Rohwer, Graduate Student, Department of Horticultural Science
Gardening is a rewarding experience for numerous reasons. One of the most apparent rewards is a beautiful display of flowers. Flowers have evolved into specialized pollination machines. Some cross-pollinated plants are anemopholous, or wind-pollinated. These plants tend to have inconspicuous flowers and produce a lot of pollen, because wind currents can not selectively identify which plants are receptive to specific pollen. Some wind-pollinated plants include oak, birch, and pine trees, as well as grasses. On the other hand, flowers pollinated by insects (entomophilous flowers) or other animals often advertise themselves. One way to advertise is by color. Birds tend to be attracted to brightly-colored flowers, especially red. Insects may be attracted to visual or ultraviolet patterns on flowers, which are not in the visual range of humans. Another interesting way for flowers to advertise is by fragrance.
flowers shed pollen on the wind.
Lavatera's pollen is obvious and well marked.
sp. voodoo lily, grown outdoors in Renton, Wa.
The underlying biological purpose of flower fragrance is to advertise to insects that food (nectar or pollen) is available, or to fool the insects into a hungry or amorous condition. The insect visits the flower, looking for food or a mate. If all goes well for the flower, the insect will take some pollen with it before it leaves, then serendipitously deposit that pollen on the stigma of another flower of the same species, thereby cross-pollinating the plants.
It is likely that flower fragrances (and essential oils of many herbs) evolved from or are chemicals originally meant to deter herbivores. Insects that visited these flowers, looking for pollen or prey to eat, were able to sense these chemicals. If the chemicals were not irritating or deterring to the insects, they would selectively visit flowers with these certain smells, which identified them as having available food. Another evolutionary scenario could be that insects that were able to successfully find a mate on a flower with a certain scent would return to a flower with that scent, looking for a mate. In either case, if the insect carried pollen with it to another flower, there is obvious potential for perpetuation of the species, and co-evolution of insects and flowers becomes feasable.
The chemicals that we sense as smells are widely varied. The distinctive perfume of jasmine (methyl jasmonate) comes from the metabolism of cell membrane components. Simpler forms of cell membrane derivatives, like short-chain ketones, aldehydes, and alcohols, give cut grass and some flowers distinctive fragrances. Other volatile compounds, like methyl salicylate (wintergreen oil), are benzoic acids, structurally related to acetylsalycilic acid, or asprin. The fragrant phenylpropanoids are related to the fragrant compounds of cinnamon and nutmeg. A large number of flower fragrances are simpler forms of the terpene resins that seep from pine trees. Specific species tend to have a specific fragrance profile combining many of these compounds.
Specific fragrance profiles attract specific insect pollinators. For example, the titan arum (Amorphophallus titanium) and carrion flower (Stapelia giganteum) attract beetles and flies that feed on or lay eggs in rotting flesh. As you may suspect, the flowers stink like rotting flesh. Different but specific scents also help to ensure that insects visit flowers of a similar species, increasing the potential for successful cross-pollination. Fragrance may serve to make it easier for insects to find the visual cues of the flowers, and fragrance probably evolved before visual flower signals. From a long distance, fragrance is more effective than visual signals at attracting a pollinator, especially to a small or hidden flower. Up close, however, the visual signals would help to accurately find the pollen or nectar.
Flowers tend to be the most fragrant when they have sufficient nutrition. In addition, moderate to warm temperatures and high light tend to increase fragrance, but fragrance also reduces the life of the individual flowers. If the flower uses energy to make fragrance, it can't use that energy to keep itself looking nice. In breeding programs for cut flowers, like roses, vase life is an important characteristic to select for. Therefore, as plants with longer flower life are selected for, fragrance is typically disregarded. The same holds true for potted and garden plants. For example, cyclamen used to have a fragrant flower. However, breeding programs have ignored fragrance, so it has been virtually bred out.
Production of many fragrances displays a circadian cycle-that is, they are stronger at certain times during the day or night. Snapdragons, for example, are more fragrant during the day, when bee pollinators are likely to be active. Nicotiana is more fragrant at night, when its moth pollinators are out and about. It would be a waste of energy for these plants to advertise to insects that don't even pollinate them!
The location of fragrance production on the flower varies. Some plants have fragrant pollen. The oily coat of the pollen may contain its own profile of fragrant compounds that is distinct from the fragrance profile of the rest of the flower. Different parts of the petal or pistil also often make fragrant compounds, and often in different quantities. Rose pollen, for instance, contains a fragrance profile separate from the rest of the flower, but fragrances from the rest of the flower usually overpower pollen smells.
As you may have noticed in your travels around the garden after a rain, scents are often stronger when the air is humid. This is because the scent molecules are able to travel farther and are easier for your nose to pick up when the air is more humid. The plants may also release more fragrant compounds under humid conditions.
Even if they don't smell, it is almost irresistible to poke your nose into a bouquet of cut flowers and take a long, deep breath. Stretching to smell the heliotrope or sweet peas on your walk around the garden is almost instinctual. Sniffing the neighbor's lilac bush is an unavoidable pleasure. If it smells good enough, you might even have your eyes closed. The next time these fragrances cross your nose and your eyes close, think about the role they play in pollination, or their floral source, or even their specific chemical profiles, but don't let these thoughts ruin your experience.
For more information on olfaction and fragrances, visit
Toasting Bordeaux (and Other Organic Fungicides)
Janna Beckerman, Extension Plant Pathologist
Many homeowners and even nursery professionals, when confronted with a disease problem, stress that they wish to apply an "organic" fungicide to control the disease, because it is more environmentally friendly. Others are equally adamant that they want something that works, regardless of the ecological impacts. Many of the organic fungicides fulfill these two most important criteria in disease management in one bottle: Efficacy with minimal ecological impact. However, it must be stressed that improper use of any chemical, synthetic or organic, will result in a failure of control AND have negative environmental consequences.
Effective use of organic fungicides (or any fungicide for that matter) requires a solid strategy of integrated plant management. As opposed to focusing on the pest or pathogen in a traditional integrated pest management (IPM) program, integrated plant management focuses on identifying the right plant for the site, and management strategies aimed at keeping that plant healthy. The backbone of integrated plant management includes carefully matching the plant to the soil type, sunlight levels and watering conditions; proper sanitation; appropriate fertilization and pruning, when necessary. All of these strategies work together to prevent disease problems from developing.
Prevention is the key word here, and it is essential to successful organic gardening because established populations of plant pathogens don't respond well to ANY chemical, organic or synthetic. The fungicides and bactericides discussed herein all have low acute toxicity to both birds and mammals (including humans). This doesn't mean you should use them indiscriminately. Copper- and sulfur-based chemicals should be used with caution-for the sake of your plants, and in the case of the copper-based fungicides, to prevent groundwater contamination (copper is a heavy metal, and toxic to fish). As always, follow label instructions carefully. Prior to applying any chemical, make certain of your diagnosis. If you are certain of your diagnosis, proceed to the next step of identifying which pesticide is best for the problem you wish to manage. Remember to determine if the plant you wish to treat is labeled, and that no contraindications exist. Finally, recognize temperature limitations, and apply during appropriate weather conditions. When applying any chemical, be sure to protect yourself using the proper precautions.
The oldest recorded fungicide is sulfur. It has been used for over 2000 years. Early in agricultural history, Greeks recognized its efficacy in controlling rust on wheat. Although few homeowners grow their own wheat, sulfur can be used as a preventive fungicide against powdery mildew, rose black spot, rusts, and other diseases. The key to its efficacy is that it prevents spore germination. For this reason, it must be applied prior to disease development for effective results. Sulfur can be applied as a dust or purchased in liquid form; It is also available as a wettable powder, which allows you to decide how you wish to apply it. Do not use sulfur if you have applied an oil spray within the last month-the combination is phytotoxic (plant-killing). Likewise, remember to NOT use sulfur when temperatures are expected to exceed 80°F. Finally, there are certain "sulfur-shy" plants including varieties of gooseberries, currants, apricots, raspberries, and cucurbits that should never be treated with sulfur.
Lime-sulfur is formed when lime is added to sulfur to help it penetrate plant tissue. It is more effective than elemental sulfur at lower concentrations; however, the odor of rotten eggs usually discourages its use over extensive plantings.
Although not the oldest fungicide, Bordeaux mixture has been successfully used for over 150 years, on fruits, vegetables and ornamentals. Unlike sulfur, Bordeaux mixture is both fungicidal and bactericidal. As such, it can be effectively used against diseases such as leaf spots caused by bacteria or fungi, powdery mildew, downy mildew and various anthracnose pathogens. The ability of Bordeaux mixture to persist through spring rains and to adhere to plants is one reason it has been so effective. Bordeaux mixture contains copper sulfate, which is acidic, neutralized by lime (calcium hydroxide), which is alkaline.
Bordeaux mixture comes in several formulations. One of the most popular, effective and least phytotoxic formulations for general home garden and orchard use is the 4-4-50 formulation (These numbers translate into four pounds copper sulfate and four pounds lime in 50 gallons of water). For determining a more useful amount, consult the Ohio State Bulletin: Controlling Insect and Disease in Home Fruit Plantings (http://ohioline.osu.edu/b780/b780_5.html).
These formulations were developed in recognition of the fact that copper, like sulfur, is phytotoxic, and that the level of toxicity is related to the age of plant tissue being treated. If Bordeaux mixture is applied in spring after the tree breaks dormancy (to prevent infection by the fire blight bacteria, Erwinia amylovera), a weaker, more dilute formulation should be used to reduce the risk of plant injury. Some labels will recommend twice as much fungicide, which translates into an 8-8-50 formulation, for other diseases or late season application. Application of Bordeaux during hot weather (above 85°F) may cause yellowing and leaf drop. Additionally, leaf burn can occur if it rains soon after a Bordeaux application. Spray oil can be added to the spray mixture to reduce the likelihood of burn. Bordeaux mixture can be applied as either as a dust or purchased as a liquid formulation. Some sensitive plants require diluting the product to one half strength (depending on the product used - see label) to avoid phytotoxicity. These include geraniums, ivy, pansy, celery, strawberry, azaleas, dogwood, and juniper. Care should be taken when applying this fungicide to young, tender leaves of apple, pear, plum or rose. Do not apply Bordeaux to corn or ornamental sorghum, which are described as copper-sensitive plants.
Growing Rubber Trees and Other Reliable Ficus Plants
Deborah Brown, Extension Horticulturist
Some of the most striking-looking and durable plants you can grow indoors belong to the genus Ficus. Known for their glossy, leathery leaves, they vary in height and growth habit as well as leaf size and shape, offering something that will appeal to just about everyone's taste in houseplants.
Rubber tree grown as shade tree in Florida.
From the old-fashioned rubber tree (Ficus elastica) to the ubiquitous weeping fig (Ficus benjamina), darling of the indoor shopping malls, they're generally undemanding and not particularly prone to pest problems. In short, they make superb houseplants for people who don't like to fuss much with their foliage.
Typically the Ficus plants we grow indoors are improved varieties of species native to India, Southeast Asia and the Malaysian Archipelago. Since they evolved in tropical and sub-tropical climates, they're able to withstand a great deal of heat, so they're an excellent choice for a sunny atrium or south-facing bay window. On the other hand, they're fairly sensitive to cold temperatures, and should not be placed near a drafty doorway in winter.
Though they'll grow vigorously in full sunlight, (many grow outdoors as landscape plants in the greater Miami area), most Ficus plants thrive indoors in bright, medium light. I've even had success growing a sprawling rubber tree in a large north-facing window that never received any direct sunlight. (OK, so they're not supposed to sprawl; it was still impressive.)
If your houseplant budget feels a bit pinched (and whose doesn't right after the holidays?) don't assume you must buy a large, mature Ficus. Instead, start with a relatively small plant. Most Ficus species grow quite rapidly with minimal attention, provided they receive adequate light. In the meantime, it's fun to brighten your home with a perky fresh plant of any size, this time of year.
There are two main concerns to keep in mind when choosing a houseplant you'd like to last for years. First and foremost is the amount of light that's available where you want to place it. Do you have enough light to support good growth for that particular plant? Second – and this is really important in choosing a Ficus – how much space can you allot the plant as it grows?
Most Ficus we grow indoors are upright, woody plants. Many are single-trunk "trees", others, multi-stemmed "shrub" forms. You'll even find novelty versions where several stems have been braided together. (These braids fuse as the plant grows older and each stem expands.)
Burgundy-leaved and standard green-leaved rubber trees.
There's also a vining form, Ficus pumila or creeping fig, that has small leaves and clings to walls by means of aerial roots. It was used to cover the series of archways inside the Cowles Conservatory at the Minneapolis Sculpture Garden, and can also be found covering the far wall (by the steps) of Como Conservatory's fern room.
Left to their own devices, Ficus plants can grow much larger than you'd expect. Luckily, they may all may be pruned to control their size. In fact, pruning tends to encourage branching and results in fuller growth – assuming there's enough light to support vigorous growth.
Prune Ficus trees and shrubs as you would any woody plant, making your cuts just above a node, where a leaf is attached to the stem, or where another stem branches off. You can also prune just above a leaf scar, even though there's no leaf there any more. New growth should arise from the scar area.
Water and fertilizing:
Water Ficus thoroughly. Don't stop until you see water coming through the pot's drain holes, then remove the extra water after a few minutes. Use room temperature or lukewarm water to avoid shocking their roots with the icy cold water that comes out of our faucets in winter.
Except for creeping fig, which should be kept moist and watered the minute the soil surface feels dry, allow Ficus plants to dry a bit between waterings. However, they do best when they aren't allowed to dry too much. It's important to retain some moisture in the root ball between waterings rather than letting the soil get bone dry.
The practice of keeping soil too wet or allowing it to get terribly dry will both result in leaf loss. And while leaf loss is primarily a nuisance in a weeping fig, it can be quite disfiguring in large-leaved plants such as fiddle-leaf figs or rubber trees. Generally speaking, those large-leaved plants don't replace lost leaves, they only grow new ones at the branch tips. Missing leaves will result in gaping holes or bare stems.
Tailor your fertilizing routine to the plant's growth cycle. When a Ficus is producing new leaves and growing actively, you can fertilize every three or four weeks, provided you mix your fertilizer 1/2 the label-recommended strength. Taper off as growth slows in autumn. It probably won't be necessary to fertilize during the short days of winter, unless your plant continues to grow well due to its location or supplementary fluorescent lighting.
Ficus benjamina or weeping fig: There are more sizes and varieties of weeping fig on the market than any other Ficus. You'll find them ranging from little table-top specimens to large "floor models." Weeping figs have lots of glossy, slightly wavy leaves.
Ficus benjamina grown in containers in Florida nursery.
These plants are notorious for dropping leaves when they're moved from one location to another; they also tend to lose them in autumn as days grow shorter. Luckily, they're capable of developing lots of new foliage fairly rapidly, as long as they get reasonable amounts of light.
Ficus elastica or rubber plant: You may find variegated as well as burgundy-colored versions of this old-fashioned favorite. With large, stiff leaves and woody stems, this plant truly has the potential to become a "tree" indoors.
Ficus lyrata or fiddle-leaf fig: This is another woody plant with lots of potential. It's leaves are even larger than those of the ordinary rubber plant. Think of it as "living sculpture."
Ficus maclellandii `Alii' really has no common name; people just call it Alii. Without a label, you'd probably never guess this plant is a Ficus. It's woody like the others, but its leaves are very long, narrow and pointed. They look a bit more like bamboo than anything else.
Ficus retusa nitida or Indian laurel: This plant is similar to the weeping fig, but its leaves are slightly larger and stiffer. And, it's not quite so fussy about change in its environment. Though it's used extensively in commercial interior landscaping, Indian laurel is less common in the marketplace. If you find one, grab it.
Solving an Insect Mystery
Jeffrey Hahn, Asstant Extension Entomologist
(with special thanks to Jay B. for his information on this case)
One of our master gardeners fielded an interesting question in October that seemed at the time to be a straightforward problem to diagnose and offer advice. Instead it turned out to be a real puzzler, ultimately taking several months before a solution was discovered. It started when a manager of a condominium posed a question to the ‘Ask a Master Gardener' web site about an outbreak of small, dark insects that they believed were flour beetles.
Foreign grain beetles|
Red flour beetles
The building manager is in charge of 536 units with 8 units per each building. The insects were first found in two units in one building in mid September (later other units discovered them including apartments in the adjacent building). However, these insects were not in kitchens where you mighty expect to find them but in the bathrooms around tubs, sinks, and on the floor. From there they apparently moved into the bedrooms. The two affected units were on the same floor but not next to each other. The tenants removed flour, cereal, and other stored product foods, scrubbed and cleaned, and even set off bug bombs but with no results. The pest management company under contract treated in early in September (and again in early October) but without any results.
The master gardener answering the question believed these insects were foreign grain beetles and not flour beetles. Foreign grain beetles and flour beetles are very similar. Both are reddish brown with the flour beetle being a little larger (1/8th inch vs. 12th inch for the foreign grain beetle). Foreign grain beetles occur in August and September, especially in new buildings because of the relatively wet green wood. Foreign grain beetles feed on mold and fungi and do not attack dry grain products. The master gardener provided a picture of a foreign grain beetle. She also inquired about the age of the building.
The owner responded that the building was not new, being built in the 1970's. She wondered instead if foreign grain beetles could be a problem due to condensation or plumbing leaks. The master gardener responded that this was possible and she should look for possible sources of extra moisture. The condominium owner discovered after further investigation that one of the tenants had allowed her shower stall to become saturated under the tile and grout, resulting in serious deterioration of the sheet rock behind it which most likely resulted in mold.
However even after the shower stall was repaired, they were not able to eliminate the insects. At this point, the manager contacted the Yard and Garden Clinic in late November for help with the problem. It was puzzling because as more of the story was told it seemed that either foreign grain beetles or flour beetles (or other type of stored product insect) could be the culprit but the situation but it also was not completely typical for either of these two insects. After discussing it with the manager we felt the best place to start was to verify the identity of the insects. The next day they submitted a sample which was identified as red flour beetles, Tribolium castaneum.
Now we at least had a direction to go but it was still unclear what was the source of the problem. The manager reiterated that the flour beetles were not being found in any kitchens. We discussed pet food and other potential sources that may not be found in the kitchen but nothing obvious was discovered. We also discussed the possibility of mice and the cache of food they collected could be a food source. Because this would be located in the walls or an attic, the source would not be apparent. However, the manager said that did not have a mouse problem.
At this point I encouraged her to talk to her pest management company. It was important that a thorough inspection be conducted to discover the source of the infestation. A manager was sent out to the condominiums and throughly inspected 16 units in the two buildings that had reported finding insects. He found flour beetles in a total of 8 units of which one unit was particularly heavily infested. In that apartment one of the elderly residents had died recently and the other had never complained about the insects. The sanitation in this apartment was quite poor with many types of stored product foods in the cupboards and a lot of food crumbs and debris on the floor. This was at least part of the source of the infestation.
The pest management professional also checked out the attics above the buildings (each row of buildings shares a common attic). Near the wall separating the two buildings with the flour beetle problems, he found many mouse droppings, along with a heavy accumulation of acorns, seeds, and other food cached by mice. Apparently, the mice were getting food from outside and storing it in the attic and in the hollow wall between the two buildings. The 8 units were adjacent to the separating wall which explained why these apartments were finding flour beetles and why they were not found in kitchens.
The pest management professional asked the condominium's management to throw away all of the infested, old stored food products in the heavily infested unit as well as clean up the crumbs and food debris. He also arranged to treat the wall between the two buildings with residual dust insecticide and set up a mouse control program to eliminate them from the attic. He asked management to clean up the seeds, acorns and other mouse-related mess and seal a ½" gap at the bottom of the wall separating the units (between the sheetrock walls and the floor) after he dusted into the wall void.
There are several lessons to be learned here. 1) Always be sure of the identity of the insect problem. This can be done without a sample but when the circumstances don't seem to fit the known habits of an insect then be sure you know which pest is causing the problem. 2) Don't underestimate the value of a complete inspection to determine the source of the problem is. Finding this source is usually a critical step in treating an insect problem. There may also be more than one source so don't stop after finding the first one. 3) Sanitation and nonchemical methods are often very important factors in eliminating an insect problem. A reliance on insecticides only to control a problem will fail if the source of the problem is not eliminated.
Get the low down on this month's insect pests at
Y & G Briefs Now on CD
Beth Jarvis, Yard & Garden Line
The Master Gardeners asked for the Yard & Garden Briefs to be put on a CD so they could access them at plant clinics, etc. So here they are, in a more convenient format, that might also be helpful to anyone who interacts with the public, especially in out of the office settings such as landscaping or retail sales.
These are the same Briefs that appear on our web site at:
The CD is both PC and Mac compatible and runs on the web browser software in your computer. For a close up look at front and back covers, click here:
The retail price is 14.99 plus 6.5% sales tax ( =$15.96) plus $2 shipping and handling. There's an order blank here that may be mailed or faxed. (We don't have a secure server set up at the moment.)
(University of Minnesota Master Gardeners and retailers should request pricing info from email@example.com.)
The picture at left is of Nicotiana, a flowering tobaccos, and one of the annuals where breeders have selected for attributes other than fragrance. Checking the Burpee catalog, I noticed that 3 of their 6 Nicotiana offerings touted their fragrance-- 'Sensation' Mix, 'Heaven Scent' and Nicotiana sylvestris 'Peace Pipe'.
We'll stick w/this sweet scented tangent for another month. In February, Kathy Zuzek will write about the rose breeding program at the Minnesota Landscape Arboretum.
Then, in March, Lee Frelich, of Forest Resources, will tell us all about the dangers of exotic earthworms (hint: none is native).
In a later issue, Doug Courneya, Regional Extension Educator, Olmstead County, will talk about buckthorn reduction. He says there's no such thing as "control" but we can reduce it.
Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.
Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/. Our home page has clickable links to most of the components of the Yard & Garden Line, such as Bell Museum of Natural History, INFO U and the Soil Testing Lab.
Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.
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