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Most citrus fruits are pretty symmetrical - think of round oranges and grapefruits, oval lemons and limes - but the Buddha’s hand citron (Citrus medica var. sarcodactylis) is anything but. This odd-looking yellow fruit, also known as fingered citron, displays as many as 20 fingerlike segments. It grows on a small tree with evergreen foliage. It’s hardy outdoors only in completely frost-free zones but can be grown in a greenhouse or conservatory in any climate.
Buddha’s hand citron is commonly grown in China, Japan, and several other Asian countries. It’s beleived to have been cultivated for nearly two thousand years. The fruits are very fragrant, combining citrus and floral notes, and have been used to perfume homes and temples.
Buddha’s hand citron contains very little pulp so it’s not a useful source of juice. But, like other citrons, the lemon-scented peel and thick, non-bitter rind are edible. The fruit is often used for making marmalade or candied peel. Fruitcake, anyone?
Nancy Rose
Have you ever experienced the frustration that comes with purchasing a plant to complement your home, or receiving a gift plant, only to have it fail in a short while? At one time or another, this has happened to all of us and the failure may have been our own doing. We may have unknowingly taken one or more of the following five steps to cause the death of our plant.
How to Kill a Houseplant Step 1: Place the plant in a site with insufficient light.
Plants require light to convert carbon dioxide and water to sugar through the process of photosynthesis. Without sufficient light to manufacture food, plants must rely on stored food reserves and as the food reserves are depleted the plant begins to die.
There are three important characteristics of light that must be considered; intensity, duration, and quality. Intensity refers to the brightness of light. Light intensity influences the plant’s ability to manufacture food as well as promotes growth and flowering. The intensity of light varies depending on the direction of the window, the season of the year, the distance the plant is placed from the window and anything that may be placed between the plant and the window. Some plants tolerate very low intensities of light while others require much higher intensities to grow and develop.
Duration, the second characteristic of light, can be defined as the length of time a plant is exposed to light. The length of time a plant receives light, commonly referred to as daylength, is important to flower bud initiation and proper shoot and leaf growth. The blooming times of poinsettias and Christmas cactus, for example, are determined by daylength.
The third characteristic, quality of light, refers to the wavelength or part of the visible spectrum available. Remember ROY G BIV(red, orange, yellow, green, blue, indigo, and violet), the mnemonic device we used in school to learn the colors of the visible spectrum or rainbow? The rays from the blue and the red ends of the spectrum are important for photosynthesis and the flowering of plants.
In many cases, good plant health can be maintained by simply moving the plant to a site where there is adequate light. This could mean moving it closer or further away from a window, placing it in a different spot in the room, or moving it into a different room entirely. But, what if your decor calls for a plant in a spot that is too dark? The answer is that you can keep the plant in that site if you supplement natural light with artificial lighting, Supplemental lighting is no longer limited to 48 inch fluorescent tubes, commonly called “shop lights”. There are not only attractive fixtures, but alternative light sources available. An advantage of using fluorescent lights is that they emit light while remaining cool to the touch and there is little danger of burning the plant’s leaves. However, while fluorescent lights emit the blue wavelengths that promote strong growth of the plants, they lack the red rays necessary for many blooming plants. By combining cool white with warm white tubes or using full-spectrum grow lights, the light needs of most plants can be met. For best performance, fluorescent light must be kept six to eight inches from the plants.
High intensity discharge (HID), also called metal halide lamps are an excellent source of blue rays and are good for leafy growth and keeping plants compact. However, they are quite expensive to purchase and to operate and they emit a large amount of heat which limits their use in many homes. Another light source is high pressure sodium (HPS) lamps. They are an excellent source of red rays that trigger budding and flowering in plants. On the negative side, they emit an orange-red glow that distorts colors which is undesirable in home settings.
How to Kill a Houseplant Step 2: Overwater the plant.
It has often been noted that while light is the greatest limiting factor to growing houseplants, overwatering is the number one killer of houseplants. Determining when to water houseplants can be challenging. The frequency of watering depends on several factors, including the type of plant, the type of container, the humidity in the air, the room temperature, the stage of plant growth, and the potting medium. Watering frequently with small amounts of water or watering plants on a schedule can lead to problems because the plant may receive either too much or too little water. Overwatering will lead to saturated soil that encourages rotting of the root hairs and later rotting of the roots themselves. Yellowing of lower leaves on the plant is symptomatic of root rot and as the rot progresses, the plant may wilt even though the soil is wet.
Most indoor plants like to dry out slightly between waterings. If the soil is dry to the touch, becomes lighter in color, and the pot feels lighter in weight, it is probably time to water. One of the best methods for determining when to water a plant is to insert your index finger into the soil up to the second joint and feel the soil. If the soil is dry at that depth, the plant should be watered. Do not allow the plant to wilt before it is watered. When watering, it is important to soak the entire soil ball. Water the plant until the water begins to collect in the saucer or tray beneath the pot. To avoid overwatering, it is important to empty or siphon any water that remains in the saucer or tray after about 20 minutes.
How to Kill a Houseplant Step 3: Fertilize the plant improperly.
The two biggest mistakes made with houseplant fertilization are to overfertilize plants growing in low light and to fertilize plants when they are not actively growing. Plants growing in low light often show weak, spindly growth which tempts us to attempt to correct it with fertilizer. In reality, the plant is suffering from low light which limits its ability to photosynthesize food and utilize the nutrients that are already present. The addition of more fertilizer just adds to the stress.
Likewise, a plant that is dormant during the naturally low light months of November through February will need fewer nutrients. Overfertilization can result in burned leaves and roots and ultimately the death of the plant. A rule of thumb that works well is to fertilize houseplants every two weeks from March through September with a water soluble fertilizer mixed at one-half the rate listed on the label. Plants grown under artificial lighting may need fertilization year round because they are not affected by seasonal light intensities.
How to Kill a Houseplant Step 4: Plant it in an unsuitable potting medium.
A plant’s soil or potting medium has three major functions: to anchor the roots of the plant, to provide the plant with minerals and nutrients, and to allow air to reach the roots. The root cells of plants carry on aerobic respiration similar to human cells and, like human cells, if they receive insufficient oxygen they will die.
Outdoor garden soils are generally too compact for good growing conditions in a pot and may harbor diseases and insects. Before garden soil can be used as a potting medium, it must be pasteurized to destroy disease organisms, insects, and weed seeds. It should then be amended with equal parts of organic matter and drainage material. Pasteurized compost or peat moss work well as organic matter while perlite or sharp builder’s sand serves as good drainage material.
There are many soilless potting mixtures on the market that vary in content and quality. When selecting a soilless medium, choose one that contains a mixture of ingredients and is of medium weight. Those that are on the lighter side usually contain straight peat moss which does not absorb water readily when it is dry and cannot adequately anchor a plant. On the positive side, soilless potting mixtures are lightweight, sterile, relatively inexpensive, and easy to use. Although a few of them may contain slow release fertilizers, most of them contain few nutrients and special attention must be given to proper fertilization of the plants.
How to Kill a Houseplant Step 5: Place the plant in an area with insufficient humidity.
Brown leaf tips and edges are often the result of low humidity in a plant’s environment. Most of our houseplants are really cultivated forms of tropical or subtropical plants and their native habitat is very humid. While their native environment has humidity of 80 percent or higher, it is impractical, if not impossible, to maintain that kind of humidity for the plants in our homes. In fact, it is very difficult to maintain humidity of 50 percent and it often falls to 15 percent or less during the winter months when our homes are heated. While 45 to 50 percent humidity would be excellent for our plants, and for us, we must be realistic and strive for a minimum humidity of 30 percent.
The humidity around houseplants can be increased slightly by grouping them together. Place the plants that require higher humidity in the center of the group. Placing the plants on evaporating trays will also enhance the humidity around them. Place pebbles, glass beads, marbles or a rack on the bottom of a tray or saucer and then keep the tray partially filled with water. To prevent saturation of the soil, it is important that the water level remain below the bottom of the pots. A room humidifier has the advantage of increasing the humidity in the entire room or home and thus allows freedom of placement of the plants. Misting is no longer recommended as a method of increasing humidity around plants. This practice is not only ineffective in raising the humidity around the plant, but also may encourage the development of fungal diseases.
You CAN Succeed with Houseplants
Without being corrected, these five steps are likely to transform any thriving houseplant into a pot of decaying plant parts. Many houseplant problems can be avoided if attention is given to plant selection. The choice of houseplants is nearly limitless, ranging from the old favorites to the many new cultivars specifically adapted for modern interiors.
First, assess the growing conditions in the spot where you want to grow the plant, giving special attention to the amount of light available. Then look for a plant that will fit into that environment. There are many good houseplant books and other resources that list recommended plants for specific sites. In addition, most come with a special tag or label that specifies the growing conditions for that particular plant. Don’t be tempted to select a plant just because it may look good in a spot. For example, a dish garden filled with cacti and succulents may fit perfectly on a bookshelf on the north side of your living room, but it requires bright light and will soon fail. Similarly, a low light plant like a dieffenbachia may look great in a corner near a south facing window, but the color of the leaves will soon bleach and turn brown because of the bright light.
Fortunately, by following recommended practices, many cultural problems can be avoided ensuring a long life of enjoyment for you and your indoor plants.
Figure 2: Needles browning due to infection by Dothistroma needle blight. Michelle Grabowski
Figure 3: Red spots and bands caused by Dothistroma needle blight. Michelle Grabowski
During the cold hard months of winter, Minnesotans are especially appreciative of the pine trees that brighten our lives by adding green to an otherwise white and brown landscape. It can be especially obvious this time of year, when those green needles fade and turn to brown, reducing not only the beauty of the landscape but the health of the tree.
Dothistroma needle blight, also known as red band disease, is a common problem on Minnesota’s pine trees. This disease is caused by the fungus >Mycosphaerella pini, and is primarily a problem on Austrian pine (Pinus nigra) and Ponderosa pine (P. ponderosa). Red (P.resinosa), mugo (P. mugo), and other pines can become infected as well. Scots pine (P. sylvestris) is relatively resistant to the disease.
Minnesotans gazing out their window at the winter landscape would recognize a pine tree infected with Dothistroma needle blight by a general browning of the needles on the lower branches of the tree. These needles may be completely dead and brown, or may be half brown (the tip) and half green (the base) with a red band dividing the two sections. Often the older needles, located close to the trunk, are more severely affected than the younger needles, located at the ends of the branches. Upon close examination, red spots and bands can be seen on the green sections of infected pine needles. Tiny black pimple-like fungal fruiting structures may be visible pushing through the surface of the needle within the red spots and bands. Although these symptoms typically first appear around September in Minnesota, if a tree has been infected for several years, dead needles and red spots may be seen at any time during the year.
The fungus that causes Dothistroma needle blight produces spores from May through October. These spores can start new infections whenever cool, wet weather occurs for several days in a row. The infections often remain symptomless until the fall. In September infected needles develop reddish brown spots, which grow into a red band that completely girdles the pine needle. At this point, the needle beyond the red band dies and turns brown. Eventually the entire needle dies and falls off. Infected needles are most common within 6 feet of the ground where humidity is typically higher.
Dothistroma needle blight can be a serious problem for landscape trees. Infected needles die and fall off prematurely. Trees with many infected needles will grow slowly or may stop growing altogether. Very young trees with a large number of infected needles can be killed by several years of disease.
Figure 4: Pine tree damaged by de-icing salt. Michelle Grabowski
Figure 5: Pine needles damaged by de-icing salt. Michelle Grabowski
Luckily there are several things that can be done to protect trees from Dothistroma needle blight. Because the fungus needs moisture on the needles to start a new infection, anything that helps keep needles dry will reduce problems with the disease. This includes spacing young trees far enough apart so that they will always have air circulation between them and other plants or buildings even as they grow larger. Removing weeds from in and around the tree will allow more air to reach the needles. Cutting off the lowest few branches will allow air to pass underneath the tree. If the tree is in a landscape with a sprinkler irrigation system make sure that water is being applied to the roots of the tree and is not spraying the needles. In low lying or other areas where cool, moist air commonly settles, plant resistant Scots pine trees instead of more susceptible pine species.
Dothistroma needle blight is a slow-moving disease that takes over a full year to complete its life cycle and several years to build up into a serious problem. Susceptible pine trees, like Austrian pines, should be monitored for the disease, but no fungicides are necessary if the disease is not present. If the disease does occur, a copper fungicide can be applied once just before buds open in the spring (typically in mid-May) and once after new needles have grown to their full length. This should protect the tree from serious disease problems. In addition, knocking off and raking up infected needles can help reduce the number of fungi that are able to survive from one growing season to the next. Always read the label completely and follow all instructions when applying a fungicide.
Another Cause of Browning Pine Needles: Salt Damage to Pines
Pine trees often suffer from salt damage when planted close to roads, driveways, and sidewalks where de-icing salt is applied. Trees can be injured by salt that is splashed onto branches by passing cars and by salt that is washed into the soil around the tree by snow melt and spring rains. Trees within 60 feet of the road are most likely to be affected. In pine trees suffering from salt damage, needles closest to the road turn brown from the tip down. Trees affected by salt damage will not have spots, bands or black pimple-like fungal fruiting bodies like those affected by a needle blight disease.
Figure 1 – Piles of shredded bark and slab wood. Note the coarse nature of the product that has been through the shredder only once.
Having arrived at the local full service garden center, you have determined two things. First, you need enough mulch to make a bulk purchase economical, and second, the bulk purchase avoids adding additional plastic bags to the waste stream. Standing in the yard one sees bins containing mulches of different colors and textures as well as prices ranging from $20 to $70 per cubic yard. How do you now determine which mulch product best fits your needs and pocket book? An understanding of the origin and characteristics of the various wood mulches will help in answering these questions.
Wood based mulches are derived from two main sources, materials harvested specifically for lumber production, and materials derived from land clearing or storm damage.
Lumbering derived products
In the lumber mill trees are debarked and squared in the process of creating lumber. The bark and slab wood produced from this process are shredded to produce mulch (Figure 1).
Figure 2 – Pine bark mulch with its flat color retention elementsBark derived products
The bark can be shredded two or more times and be processed through different screen sizes to produce a more finely textured product. Most locally produced mulch is a mix of hardwoods including basswood, alder, quaking aspen, various oak species, various maple species, and birch. Traditionally, the local double shredded mixed hardwood bark mulch has the shortest life span (1 to 2 years) and is the least expensive (Table 1).
Mulch produced from pine bark has uniquely layered pieces and maintains its colors longer than other mulches (Figure 2). This feature adds value and price to pine bark mulch which is expected to last 2 to 3 years (Table 1).
Exotic bark mulches
Exotic mulches such as the shredded bark of cypress and several cedars are often the most expensive. The higher price is a function of the greater transportation costs, longer color retention, and longer practical life of the mulch, up to 4 years (Table 1).
Figure 3 – Colored mulches provide design possibilitiesSlab wood derived products
The material from the shredded slab wood is made up of wood fibers that will accept coloring as opposed to the bark, which will not (Figure 3). Price increases cover the costs involved in additional shredding and coloring. These mulches tend to have a two to three year life span (Table 1). Colored mulches find their place in the landscape when the color of the mulch compliments the other colors present or presents a color feature of its own. Lighter colored mulch placed in a shaded area can bring additional light to the design.
Playground Safety Materials
Wood mulch material can also be processed in such a way as to greatly reduce the chance of creating splinters. When applied at depths of a foot or more this material can be placed around playground equipment where it has a cushioning effect reducing injuries sustained from falling (Figure 4).
Wood Chips
Avoid the use of wood chips as mulch in areas requiring erosion control. Wood chips tend to float away with water movement as opposed to fibrous bark products that cling to each other, are less subject to floating, and resist movement.
Land clearing or storm damage derived mulches
All of the characteristics previously mentioned apply to mulch derived from this part of the wood stream. The quality of mulch will be a function of the way the materials were handled. If the small stems and leaves have been properly separated, then mulch from this source should be equal in quality to lumber derived materials. If these materials have not been separated, the mulch will have a less uniform texture and will break down more rapidly.
Value Determination
Your personal value determination will likely be influenced by your sensory preferences, your financial resources, and priorities.
Color
You will pay more for lasting color whether this is applied or natural. Part of the value of the cedar and cypress mulches is that they will retain their natural color for a year3. Depending on sun exposure color can sometimes be revived by raking to bring unexposed materials to the surface.
Scent
Most mulch emits a pleasing wood based scent. The scent from the exotic mulches may last a little longer, and depending on one’s olfactory abilities and preferences this character may contribute to your value determination.
Longevity
If your goal is to have mulch function as a soil amendment factor then the more rapidly degrading mulches will achieve this goal. This will require amendment on a yearly or every other year basis (Table 1). If your goal is to have the mulch last as long as possible then the exotic bark mulches will achieve this goal. What influences longevity?
The longevity of mulch is influenced by the physical and chemical characteristics of the mulch, as well as the environment in which the mulch is placed.
The best predictor of longevity relative to mulches’ chemical characteristics is the lignin to nitrogen ratio (lignin: N) in the woody material1. The higher the (lignin: N) ratio the greater the longevity of the mulch. This is due to the difficulty that soil bacteria and fungi have in metabolizing lignin and their need for nitrogen to accomplish this purpose.
Relative to physical characteristics the smaller the particle sizes of the mulch the shorter its practical life span.
The environmental influences on mulch longevity are based on the favorability of the growth conditions for the soil bacteria and fungi degrading the mulch. Favorable growth conditions would be a function of temperature, moisture, and nutrients. In practical terms the factors would include the length of the growing season and degree of sun exposure, the availability of moisture and irrigation practices, and the availability of nitrogen and fertilization practices2. General estimates for longevity are indicated in Table 1.
Table 1
Conclusion
First, take a close look at the mulch you are about to purchase. Look for uniformity in particle size, and the lack of twigs, leaves and non-wood waste products. Second, determine which characteristics are most important to you - the mulch’s role as a soil amender, the color, the scent, and or the longevity and time between applications. Lastly, regardless of your specific mulch preferences take note of the fact that application of mulch will benefit your plants and contribute to the welcome home atmosphere of your landscape.
References
1. Mary L. Duryea, R. Jeffery English, and L. Annie Hermansen, A Comparison of Landscape Mulches: Chemical, Allelopathic, and Decomposition, Journal of Arboriculture 25(2): March 1999.
2. Stenn Design, Woody Mulch Research Review, Professional Users and Product Availability Surveys, December 2004 Stenn Design
3. Mary L. Duryea, Landscape Mulches: How Long Do They Retain Their Color?, Document FOR 68, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, First published July 1999, Reviewed September 2006. http://edis.ifas.ufl.edu.
Tree seedlings in natural settings don’t have it easy. They have to fight through significant competition in order to gain a foothold and ultimately grow above adjacent herbaceous plants and smaller woody species. Due to their height advantage and ever expanding root system, they become proficient at intercepting light, nutrients, and water. Competition for resources eventually influences the composition, growth rate, and densities of other plant populations growing under large trees. Maturing trees in our landscapes have increasing resource demands which can affect the growth of adjacent shrubs and herbaceous plants. Landscapes are dynamic and we can anticipate the changes in growing conditions over time and be proactive. We choose plant species and maintenance strategies from the start that are most amenable to our landscape intentions. Even if we find ourselves in a challenging situation where lawns, shrubs, or herbaceous perennials are dying out due to tree competition, there are a number of possibilities we can pursue to revitalize these areas and make them more attractive.
Trees limit resources available to nearby plants
Spring ephemerals like Siberian squill take advantage of available sunlight before trees leaf out. D. Zlesak
Ajuga 'Catlin's Giant' makes a nice groundcover under a magnolia. D. Zlesak
Hostas are a tough and reliable option tolerant of competition from trees. D. Zlesak
The primary challenges for plants growing under trees are reduced light levels and limited moisture and nutrient availability. Tree species that have finer foliage and more open canopies such as honeylocust (Gleditsia triacanthos) and Kentucky coffeetree (Gymnocladus dioicus) let more light through than more densely foliaged species. Such trees are better choices in landscape situations where understory plantings are desired. If one has a tree with a relatively dense canopy such as a Norway maple (Acer platanoides), it is possible to open up the canopy and let more light through by selective pruning, but overpruning can negatively affect the tree. Besides pruning and choosing more amenable tree species for higher light penetration, one can select plants to use under trees having greater shade tolerance.
Many shade tolerant ornamental species grow naturally as understory plants in wooded areas. Just a few of many woodland wildflowers to choose include hepatica (Hepatica ssp.), Jack in the pulpit (Arisaema triphyllum), sweet woodruff (Galium odoratum), and woodland phlox (Phlox divaricata). Some shade tolerant shrubs include alpine currant (Ribes alpinum), leatherwood (Dirca palustris), false spirea (Sorbaria sorbifolia), and ninebark (Physocarpus opulifolius).
Reduced moisture and nutrient availability is another factor making gardening under trees difficult. The majority of the root system of a typical tree is within the top foot of the soil and root spread is typically well beyond the dripline of the branches. Trees can develop a very dense root system in the upper soil surface allowing them to be quite efficient at absorbing moisture and nutrients. Providing routine supplemental irrigation to plants growing under trees can be very useful, especially if the soil type does not hold water well. In addition, mulch is also very useful to conserve moisture. Organic mulches can also provide nutrients and improve soil structure as they decompose. Having periodic soil tests conducted will help to determine nutrient levels and determine fertilization rates. There is often a higher nutrient demand for a given unit of soil where trees and other plants grow in close proximity.
Planting considerations under trees
Pots of shade tolerant annuals brighten a shady spot under a maple tree
Reduced light and high competition for moisture contributed to a thin, weedy lawn under this spruce
The process of planting under trees can be especially challenging because of navigating around tree roots. Thick tree roots can be near or above the soil surface making it difficult to dig and place plants exactly where we would like them. Avoid injuring tree roots in the process as much as possible. Do not use tillers or other power equipment to dig or cultivate near trees and use shovels and other manual cultivation tools sparingly and carefully.
Because the soil around trees can be quite dense with tree roots, people commonly think it would be easier to create raised beds around trees to plant into. This is not recommended because the addition of soil, especially if more than a couple inches deep and covering a wide area, can limit oxygen to the tree roots beneath. It is also important not to build the soil level up near the tree trunk. Having soil and mulch piled up against the tree trunk can eventually lead to encircling roots developing and encourage decay. In addition, tree roots can eventually grow into the raised beds making it difficult once again to dig. Instead, work carefully with the existing grade around trees.
Besides sheer size, some trees limit competitors by exuding chemicals that inhibit the growth of other plants (allelopathy). Such trees include black walnut and some pines. If you have an allelopathic tree species you would like to keep, the choices of what can be grown under it are more limited. For instance, black walnut produces a chemical called juglone (5 hydroxy-1, 4-napthoquinone). Some plants that show greater tolerance to it include hosta, forsythia, and pachysandra.
Following are some options to consider when gardening under trees:
• Favor the use of perennial species to keep soil disturbance to a minimum.
• Consider attractive alternatives to having in-ground plantings, especially close to the base of a tree. Alternatives include the use of decorative mulches and statuary. In addition, decorative pots can be carefully placed on top of or barely into the soil to grow some colorful, shade tolerant plants. This avoids competition for water and nutrients from tree roots.
• Grow spring ephemerals under deciduous trees. They take advantage of the sun available in the spring before the trees are fully leafed out and typically go dormant by early summer when conditions become increasingly shady. Bloodroot (Sanguinaria canadensis), Dutchman’s breeches (Dicentra cucullaria), and Siberian squill (Scilla siberica) are a few examples.
• Groundcovers with dense, spreading growth habits are a great option for use as a low-growing, living mulch. If the site is too dry or shady, they may not fill in densely. Examples of vigorous, shade tolerant groundcovers include variegated bishop’s weed (Aegopodium podagraria), lamium (Lamium maculatum), and pachysandra (Pachysandra terminalis).
• Localized individual or groups of plants may be placed with additional topsoil near a tree. This is an alternative to adding a complete blanket of topsoil around a tree. Using this approach can allow for smaller or no holes being dug and avoid damaging tree roots. This can be a great way to add pockets of hostas and other shade tolerant perennials where slight variations in topography are not problematic.
• Use smaller transplants so the holes don’t need to be as large. This makes the planting process easier and results in less tree root disturbance..
• Consider checking for moisture levels and providing supplemental irrigation as needed for plantings under trees and replenishing mulch as needed to conserve moisture.
Aphids on hibiscus. J. Hahn
This is the time of year when we need to watch our houseplants for insect and mite pests. In some cases these pests may have been brought into homes on plants that were kept outdoors during the summer. In other instances they may have flown in or have been blown into homes; these pests are so small, they do not have any problem passing through screens. These insects and mites may have also hitched a ride indoors on live Christmas trees or holiday wreaths.
Watch for discolored leaves but be aware that not all yellowing or browning foliage indicates an insect or mite problem. Also keep an eye out for webbing which often indicates spider mites. Use a magnifying lens to help you detect these pests, as they are very small. You may also be able to find certain pests, especially spider mites, by tapping leaves while holding a white sheet of paper underneath. Watch for tiny creatures that may fall onto the paper. You can also set out yellow sticky cards to alert you to the presence of whiteflies, thrips, fungus gnats, and winged aphids.
Treat any infested plants you find right away. It is much easier to control light infestations compared to heavy ones. You can usually control light infestations by wiping off the pests using a paper towel or soft rag dipped in alcohol (do not wash hairy plants, such as African violets). You could also try a mild detergent solution (1/2 teaspoon per quart of lukewarm water) to wipe of small numbers of insects. Be careful though since soap can potentially be phytotoxic to the plants. If an insect problem is confined to a few leaves or branches it may be easier to just prune out those areas especially if the infestation is severe.
If alcohol or soap is not effective or you encounter a more severe infestation, you may wish to use an insecticide treatment. There are a variety of a products that are available. The following is a list of active ingredients that you can find in stores selling home insecticides. Most are available in aerosol or liquid ready-to-use containers.
Mealybugs on philodendren. J. Hahn
Beta-cyfluthrin (e.g. Bayer Advanced Dual Action Rose & Flower Insect Killer [combined with imidacloprid]). This is generally effective against scale, mealybugs, whiteflies, thrips, and aphids. This has a moderate residual and can be effective at least several days.
Permethrin (e.g Shultz Houseplant & Garden Insect Killer [combined with d-trans allethrin]) Generally effective against scale, mealybugs, whiteflies, thrips, aphids. This has a moderate residual and can be effective at least several days.
Resmethrin (e.g. Bonide Houseplant Helper, Bonide Whitefly and Mealybug, and Fertilome Whitefly & Mealybug Killer). Generally effective against scale, mealybugs, whiteflies, thrips, aphids. Has a short residual, lasting a day or less.
Pyrethrins (e.g. Shultz Houseplant & Garden Insect Spray) This is generally effective on mealybugs, whiteflies, scale, thrips, aphids. No residual, only kills on contact.
Tau Fluvalinate (e.g. Bayer Advanced 3 in 1 Insect, Disease & Mite Control [combined with imidacloprid]). This product is labeled for spider mites, although it is not clear how effective it is against them.
Imidacloprid (e.g. Bayer Advanced 3 in 1 Insect, Disease & Mite Control [combined with tau-fluvinate] and Bayer Advanced Dual Action Rose & Flower Insect Killer [combined with beta-cyfluthrin]). Imidacloprid is a systemic insecticide that is applied to leaves and stems. It is generally effective against mealybugs, scale, and aphids.
Disulfoton (e.g. Bonide Systemic Houseplant Insect Control). This is a systemic insecticide that is applied as granules to the soil. It typically has a disagreeable odor. Do not use unless the plant is actively growing. It is generally effective on mealybugs, scale, and aphids.
Spider mite damage on ivy. J. Hahn
Potassium fatty acids (e.g. Bonide Insecticidal Soap, Garden Safe® Brand Insecticidal Soap). This product is thought to kill insects and mites by disrupting their cell membranes. It only kills what it directly contacts and does not have residual activity. It is generally effective against scale, aphids, thrips, and spider mites.
Neem (e.g. Bonide Bon-Neem). This is a botanical insecticide that disrupts the life cycle of some insects. It is generally effective against whiteflies, thrips, aphids.
Petroleum oil (e.g. Bonide All Seasons® Bug Beater Horticultural Spray Oil). This product covers and suffocates target insects. It is generally effective against scale, aphids, whiteflies, spider mites.
Bacillus thuringiensis H 14 (e.g. Gardens Alive Knock Out Gnats™). This naturally occurring soil bacterium is specific to fungus gnats larvae. It is applied to the soil. This product is available primarily by mail order.
If, despite your best efforts, a houseplant is heavily infested and badly damaged, your best bet is to throw it away. It is better to lose one plant than risk others becoming infested. If you are reluctant to discard the plant, prune it practically to the soil. If it resprouts, watch new growth carefully for signs of infestation.
Osteospermum Asti White. All-America Selections.
The All-America Selections organization honors a selection of new seed-grown flower and vegetable varieties each year. AAS winners are selected for their outstanding performance in field trials conducted at locations throughout the country. There are also many AAS display gardens where winning selections are grown for public viewing (see list at end of article for AAS display gardens in Minnesota).
Since its beginnings in 1932 AAS has selected as many as 32 winners in one year (1934) and as few as one (1954 and 1976). 2008 is on the low side with only 3 new varieties selected. And the winners are...
• Asti White osteospermum (also known as cape daisy or African daisy; Osteospermum ecklonis Asti White) grows about 18 inches tall and wide. It has white ray flowers (“petals”) and blue disc flowers in the center. The species is a perennial subshrub in its native South Africa but this selection can be grown as an annual here. Be forewarned, though, that it takes a full 17 weeks from sowing seeds until the first flowers open, so home gardeners will need to start seeds quite early indoors. Plants of Asti White osteospermum will also be available at garden centers. This pretty flower tolerates fairly dry soil conditions.
• Skippy XL Plum-Gold viola (Viola cornuta Skippy XL Plum-Gold) has cheerful whiskered flowers in shades of reddish purple and gold. The floriferous plants grow just 6 to 8 inches tall. Like its closely related cousins, the pansies, violas thrive in cool conditions and are one of the first flowers we can safely plant out in the spring. Start seeds of this viola indoors 10 weeks before planting out, or look for plants at local garden centers this spring.
• Hansel eggplant provides a handsome 2 to 3 foot tall plant that produces many cylindrical deep purple fruits in mid to late summer. The eggplants can be harvested at a petite 3 inch size or allowed to grow to 10 inches long - quite convenient for gardeners who go on a week’s vacation as the eggplants are ripening! Plant this eggplant in a warm sunny site in the garden or in containers.
To view many new flower and vegetable varieties, visit these AAS display garden sites in Minnesota:
U of M North Central Research and Outreach Center
1861 Hwy. 169 East
Grand Rapids, MN 55744U of M West Central Research and Outreach Center
46352 State Highway 329
Morris, MN 56267U of M Display and Trial Garden
Corner of Gortner and Folwell Avenue
St. Paul, MN 55108Minnesota Landscape Arboretum
3675 Arboretum Drive
Chaska, MN 55318Lyndale Park Gardens
4125 E. Lake Harriet Pkwy.
Minneapolis MN 55409
A pileated woodpecker drinking water from a heated birdbath. Nancy Rose
Indoors
Keep houseplants - including holiday gifts like poinsettias and Christmas cactus - evenly watered (see Carl Hoffman’s article in this issue). Dry indoor air and a sunny window location can result in quick drying of potting mix. Reduce or eliminate fertilization during the shortest days of winter.
Check houseplants for insects regularly. Move plants into the sink or shower and wash the leaves every couple of weeks - this removes dust and helps keep spider mites under control. An exception - don’t wet fuzzy-leaved plants like African violets. See Jeff’s article for more information.
If you still have dormant amaryllis (Hippeastrum) downstairs or in a closet remember to bring them up and water the pot as new growth appears.
Settle in with a stack of catalogs and do some garden planning.
If you’re in the Twin Cities area, take a break and breath some wonderfully warm, humid air at the Marjorie McNeely Conservatory at Como Park in St. Paul.
Outdoors
Our early snow has made a great insulative mulch over lawns and gardens. You can still put mulch such as straw, wood chips, or branches cut from discarded Christmas trees directly over the snow to add protection in bulb and perennial beds.
January is still a little early for most pruning since pruning wounds will be exposed to dry air for months. This can cause additional dieback on pruned stems, especially fruit trees.
If ice or heavy snow bends your shrubs over, don’t whack at the branches to remove it. Let ice melt on its own. If you really want to remove heavy snow, use a gentle upward sweeping motion with a broom.
A heated birdbath provides open water for drinking and bathing and will attract lots of birds to your yard, deck, or patio.
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Happy gardening!Nancy Rose
Editor
Regional Extension Educator - Horticulture
A Note to Readers:
After surviving 17 Minnesota winters I'm moving to a warmer climate to start my new job as editor at the Arnold Arboretum of Harvard University. Boston's really not much farther south than the Twin Cities, but, thanks to the Atlantic Ocean, I'll be able to grow those Zone 6 plants I've been coveting for years. My colleague David Zlesak will take over as editor of the Yard & Garden News. He and all the other knowledgeable contributors to this newsletter will continue to bring you timely, research-based gardening information to help you throughout the year.
