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What’re those weird white growths all over the roots of this snow pea plant? These are nodules that are formed when a beneficial soil-dwelling bacteria (Rhizobium) gets into the root cells of legumes like peas, beans, and peanuts. The bacteria lives in these nodules and fixes nitrogen. No, the nitrogen isn’t broken - - in this case, “fixing” means that the bacteria actually changes the unusable form of nitrogen (N2) into the ammonia form of nitrogen (NH3) that the plant needs to grow and thrive.
This time of year, mentions of mistletoe bring up happy images of Christmas and all of the traditions that go along with the holidays. At one time mistletoe was believed to have magical powers to ward off evil, grant fertility, block lightning, and bring together warring spouses. The truth is that mistletoe is a parasitic plant capable of killing not just one tree, but large sections of forest if left unchecked. The type of mistletoe used as a Christmas decoration does not live in Minnesota, but its relative Eastern Spruce Dwarf Mistletoe (Arceuthobium pusillum) does. This parasitic plant most commonly attacks black and white spruce (Picea mariana and Picea glauca). Mistletoe can also attack white pine, red pine, jack pine, eastern larch, balsam fir, and Colorado spruce. These trees are typically only infected with mistletoe when planted close to groups of spruce infected with the parasite.
Trees parasitized by dwarf mistletoe are most easily recognized by clumps of branches all arising from the same point on a larger branch. These clumps are known as witches’-brooms, and the needles in this clump remain green while the needles in the rest of the tree progressively turn yellow and fall off. Just before the tree dies, the only needles remaining on the tree are in the witches’-broom.
Close examination of a witches’-broom will reveal small greenish brown shoots covered in scales, less than 1 inch tall, growing directly from the tree branch. These shoots belong to the mistletoe plant. The scales are reduced leaves that no longer need to collect sunlight and produce energy for the plant. Instead the mistletoe plant uses root like structures buried deep in the bark and wood of the parasitized tree to steal all of the water, nutrients, and sugars it needs. It is this theft that results in the decline and eventual death of the tree.
Living their entire lives in a host tree, mistletoe plants have developed complex means of spreading seed to a new host. The female flower of the mistletoe plant can shoot seeds up to 55 ft. away. These seeds are covered by a sticky layer called viscin. Viscin causes the seeds to stick to needles and branches of nearby trees or to the fur, feather, and feet of passing animals. When wet, the viscin acts like a lubricant allowing the seeds to slide - down a needle or off a foot - and come to rest on the branch of a tree. As it dries the viscin becomes hard and acts like cement, permanently fixing the seed to the branch. The seed then germinates and colonizes the wood and bark of its new host tree.
There will be no symptoms of the mistletoe infection until 2 years after the seed germinates. Then a slight swelling of the branch can be seen at the infection point. It is not until 4-5 years after the seed lands on the host tree that the first mistletoe shoots can be seen growing out of the tree branch. From that point on the mistletoe plant will produce new shoots and flowers every year until the tree dies.
It is very difficult to cure trees of a mistletoe infection. The parasite is able to colonize many areas of the tree before the first symptoms can be seen. Pruning out branches with witches’-brooms and mistletoe shoots at the point where the branch meets the trunk can help increase the vigor of the tree. In many cases, however, the mistletoe reappears in 2-3 years from seed or roots already colonizing the bark and wood of the host trunk that were not visible at the time of pruning.
If more than 50% of the tree’s branches have mistletoe, witches’-brooms, or have been killed by the infection, the tree should be removed. Removing parasitized trees will prevent the parasite from spreading to nearby spruce and other conifers. In managed forest stands, the USDA Forest Service recommends removing all susceptible spruce trees at a site with eastern dwarf mistletoe because even healthy looking trees can be infected and allow the parasite to survive and spread to new trees.
For more information about Eastern Dwarf Mistletoe please read ‘Forest Insect and Disease Leaflet NA-PR-04-06’ by Baker, O’Brien, Mathiasen, and Ostry at http://www.na.fs.fed.us/fhp/
Many people have heard of the new Tropical Encounters Exhibit at the Marjorie McNeely Conservatory and Como Zoo in St. Paul that opened recently last November. The workers of the Conservatory brought together a fascinating array of exotic plants and animals for visitors to view as they walk through the exhibit. However, an unexpected addition was recently discovered there. A tropical ant, known as Cardiocondyla emeryi (no common name) was discovered on an ice cream bean tree, Inga edulis. This ant was probably accidently brought up in soil or plants shipped to the Conservatory from Florida.
Cardiocondyla emeryi (pronounced car-dee-oh-con-DYE-la EM-er-ee-eye) is very small, measuring no more than 2 mm (about 1/12th inch) in length. It is a light brown color with a dark colored abdomen. It has a 12 -segmented antennae with a three segmented club and reasonably long spines on the back of its thorax. This ant belongs to the ant subfamily Myrmacinae and on that level is related to pavement ants, thief ants, acrobat ants, and pharaoh ants, all common ants in Minnesota. One of the distinguishing features of this group of ants is their two-segmented petiole (the slender abdominal segment that joins the rest of the abdomen with the thorax).
This ant is probably from Africa originally but is easily transported through commerce and other human activity and is commonly referred to as a tramp ant. It is widely distributed and is now found in many tropical areas in Central and South America, various Caribbean islands, Africa, southeast Asia, and various Pacific Islands. Cardiocondyla emeryi had been recorded previously from three states in the U.S., Florida, Texas, and Hawaii. Although it is not clear how abundant this species is in Florida and Texas, Cardiocondyla emeryi is considered to be widespread in Hawaii.
Cardiocondyla emeryi is a ground nesting species, often found at the base of trees or in leaf litter where they produce a small-sized nest. Related species of Cardiocondyla in New Guinea were discovered to have nests containing only between 50 and 70 ants. Cardiocondyla spp. exhibit an interesting behavior for food recruitment called “tandem running”. Once a worker discovers food, it returns to the nest and recruits just a single nestmate. They both set out to the food source with the two maintaining antennal contact. This is considered to be a primitive method of food recruitment amongst ants.
This genus of ant is also interesting because there are two types of males that differ in appearance, physiology, and behavior. The ergatoid males are wingless and aggressive. They produce sperm throughout their entire adult lives and attempt to kill their male rivals for a chance to mate with new queens. However, winged males are gentle and unaggressive and produce a finite amount of sperm which they keep stored within their reproductive system. They can mate with queens in their nest, but typically leave, finding queens from other colonies to mate with. Interestingly the ergatoid males rarely attack the winged males. (From J. Heinze, B. Hölldobler, K. Yamauchi in Behavioral Ecology and Sociobiology, Vol. 42, No. 4 / April, 1998).
There should be concern whenever an exotic species is found outside its normal range. Fortunately, there isn’t any federal quarantine in the U.S. for Cardiocondyla emeryi,probably because it is already generally widespread and easily transported. It doesn’t seem likely these ants would survive outside the exhibit area, however it is unclear how widespread they could become. There isn’t any immediate concern about this ant being in the exhibit, although it will become important at some point to attempt to eliminate them. The workers, of course, will be very careful to avoid accidental injury to any of the exhibit’s fauna or flora.
The holidays have come and gone and we’re faced with the task of putting away the festive decorations. One question that often lingers is if we should keep or dispose of holiday plants. We may have sentimental associations with some plants because they were given to us as gifts, while others we purchased ourselves. Seeing brightly colored bracts on poinsettias or a few colorful petals left on a cyclamen usually sways me to keep them around, at least a bit longer. Having a blooming plant of almost any sort helps to make a winter day in January more bearable. The time eventually comes when the final decision is made to adopt these plants into our “family” of houseplants or send them on their way as a passing holiday visitor. Here are some considerations to help make your decision about four major holiday plants.
Difficult to keep as houseplants:
Poinsettia (Euphorbia pulcherrima)- Fifty years ago poinsettia bracts (modified leaves that turn color near the small, true flowers) seldom lasted more than a few weeks. Cut poinsettia stems were once common flowers in holiday arrangements. Modern cultivars have longer lasting bracts than ever, often lasting up to a few months. I was amazed a couple years ago after having a poinsettia keep its colorful bracts all the way until May!
Better branching and more compact plant habits have also contributed to the success of modern potted poinsettia cultivars. Because of their durability as potted plants, poinsettias are now almost exclusively sold as a potted plant during the holidays. Standard, long-lasting, easy to ship cut flowers in shades of pink and red (e.g. carnations and roses) have replaced much of the cut poinsettia market in the U. S.
Poinsettias are challenging to keep as houseplants because they seldom receive enough light in the home environment to thrive. They are rather susceptible to root rot which is exacerbated by water stress (overwatering or allowing pots to dry out too much between waterings). In subsequent years poinsettias are challenging to bring into bloom again. They are short-day-flowering plants and need long, uninterrupted nights for flower initiation and development. They are also very susceptible to whiteflies. Unless one has a very bright window or greenhouse, poinsettias typically limp along, seldom bloom in subsequent years, and generally do not thrive.
In the past I’ve enjoyed using poinsettias as annual foliage plants in sunny areas of garden beds or in large pots on the deck. Harden poinsettias off as any other houseplant or bedding plant before moving them to sunny outdoor conditions. A healthy 4-6” potted poinsettia can produce several vigorous stems and grow to 3-4’ by fall. In Mexico and Central America where they are native, poinsettias develop into large shrubs (to 10 or more feet tall).
Cyclamen (Cyclamen persicum)- Through the efforts of the late Dr. Richard Widmer (University of Minnesota Department of Horticultural Science) and his students, modern cyclamen culture can bring a seedling into flower in less than a year. This is accomplished through careful temperature manipulation, the use of the plant hormone gibberellic acid, and more amenable varieties. Quick generation time from seed has allowed cyclamen to become much more economical to produce and subsequently more widely available. In years past cyclamen were primarily available from Valentine’s Day through Mother’s Day. However, ease of production and bright red, pink, or white flowered cultivars are allowing this versatile plant to become a Christmas favorite as well.
Cyclamen bloom over an extended period of time. In order to keep young flower buds forming in the crown of the plant and developing into mature flowers, plants should be grown in a cool location with bright light. Removal of spent flowers can also help to encourage more flowers to develop. When deadheading, grab the spent flower stem securely and pull it completely off from the crown of the plant.
Cyclamen typically go dormant after flowering. As plants go dormant, leaves yellow and energy is diverted into the swollen, tuberous root. Sometimes the newest leaves remain green and plants do not completely go dormant. It is very difficult in the home environment to grow a compact, high quality cyclamen plant. Typically, light levels are not high enough and result in puny looking plants with elongated leaf petioles falling over the edge of the pot as they reach towards light. Unfortunately, flowering potted cyclamen are not reliably hardy to overwinter in Minnesota.
The genus Cyclamen contains about 20 species which are all native to the Mediterranean region. Cyclamen persicum needs cold hardiness Zones 8 or warmer to reliably survive. Sometimes we see C. hederifolium (hardy cyclamen) for sale as an herbaceous perennial. The flowers of this species are typically white or pink. Although C. hederifolium is listed as a Zone 5 plant, it can be successfully grown in Minnesota in protected locations.
Easier to keep as houseplants:
Norfolk Island pine (Araucaria heterophylla) is commonly sold around the holidays as an indoor, living Christmas tree. Plants are typically sprayed with glitter, decorated with small bows and other ornaments, and have their pots covered with festive foil or other plastic pot covers. Norfolk Island pine is probably the most amenable conifer to home conditions. It becomes a very large tree (up to 200 ft. tall) in its native habitat on the Norfolk Islands and Australia. The Norfolk Islands are East of Australia and were named in honor of the Duchess of Norfolk.
These plants are seed-propagated and often more than one seedling is grown per pot. Multiple seedlings in a pot allows for fuller, salable pots sooner. Once home, seedlings can be potted individually or extra ones thinned to help promote a single-stemmed specimen with the characteristic whorls of symmetrical branches radiating from the main stem. If seedlings continue to grow together they will become overcrowded and increasingly compete for light and nutrients. Without thinning or separating, some plants typically grow much more vigorously than others. This results in pots with plants of different sizes and eventually overall pots and individual seedlings with poor form. Variability in plant size and vigor in a single pot can be due to genetic differences between seedlings and differences in light and nutrient availability.
Norfolk Island pine should not be exposed to freezing temperatures because tender new growth or the whole plant can be killed. An accompanying picture highlights a row of Norfolk Island pines inadvertently used as outdoor greenery over the holidays in St. Paul. By the time the picture was taken the plants experienced temperatures in the teens and are severely damaged. Plants grow best at relatively warm temperatures, uniformly moist, well-draining soil, and high humidity. Minnesota homes often do not have adequate humidity for Norfolk Island pines to thrive. Under low humidity tips of new growth and older needles can become brown. Prolonged periods of low humidity can also result in older branches completely dying. Increasing humidity around plants by misting, putting bowls of water on radiators and other warm places, or using humidifiers benefit not only Norfolk Island pines, but other humidity loving plants such as ferns and African violets.
Araucaria bidwillii (Bunya-bunya tree) is a close relative to Norfolk Island pine and is also is very amenable to culture in the home environment. The needles are much wider than Norfolk Island pine and are typically dark green and glossy. In many ways the bunya-bunya tree makes a more attractive houseplant than Norfolk Island Pine, especially as a larger plant. The drawbacks to bunya-bunya tree is that the needle tips are rather pointed and sharp and as young plants their larger needles do not look as attractive for the holiday Christmas tree market as Norfolk Island pine.
Christmas cactus (Schlumbergera ×buckleyi) is probably the easiest holiday plant to grow in the typical home. Many people have a special Christmas cactus clone preserved over generations as a family heirloom. Such clones have typically been widely propagated and shared among relatives and friends. Christmas cactus is Schlumbergera × buckleyi, an interspecific hybrid first developed by growers in England as a cross between two Schlumbergera species, S. truncata (Thanksgiving cactus) and S. russelliana. The genus was named in honor of Frédéric Schlumberger, a French collector of cacti. Schlumbergera species are primarily epiphytic species and are native to rainforests of eastern Brazil. They are found growing within branch angles of trees and other locations with pockets of typically well-draining organic debris. Unlike desert cacti, members of this genus prefer being grown like our typical houseplants with moist, well-draining soil.
Expeditions to Brazil to collect Schlumbergera species, especially in the past couple decades, have led to greater diversity in cultivated Schlumbergera. Such germplasm is sold directly to cacti enthusiasts and is being used in breeding programs. There already is greater diversity in modern popular cultivars of Christmas cactus from recent breeding efforts. This is evident in the larger flowers and wider selection of colors now available.
Christmas cactus do not have traditional leaves. The pads (known botanically as phylloclads) that we see on Christmas cactus are actually flattened stem tissue. Each pad is a stem segment. Single pads or a section of several joined pads can be broken off a mother plant and rooted as a cutting.
One routinely asked question is how a person can get their Christmas cactus to bloom again. Temperature and day length (actually perceived as night length) are the two main cues which trigger flowering in this plant. At temperatures in the 50s°F plants typically set and develop flower buds under both short and long day photoperiods. If the temperatures are in the 60s to mid 70s, short days are necessary (long uninterrupted nights of at least 14 hours) for flowering. If temperatures are above the mid-70s, Christmas cactus typically does not flower under any photoperiod. Cooler temperatures will help opening flowers last longer. In addition, providing extra water during flowering will help to keep flower buds from dropping and allow flowers to open well and last longer.
To stay or go
Holiday plants help add to the festivity of the season and using them to decorate has become a tradition for many of us. Understanding the limitations we have in growing space as well as the conditions imposed by the home environment will help us decide which plants are reasonable to keep as houseplants and which can be considered disposable.
Photos: David Zlesak
Thanks to Linder’s Greenhouse for providing sample plants.
Each year the All-America Selections organization names a handful of new seed-grown flower and vegetable varieties as the top of the crop for gardeners. 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.)
'Fresh Look Gold' Celosia
'Opera Supreme Pink Morn' Petunia
'Pacifica Burgandy Halo' Vinca
'Holy Mole' Pepper
Only three flower varieties made the cut this year. They are all annuals and all three should perform very well in Minnesota gardens.
‘Fresh Look Gold’ is the newest plumed celosia to be named an AAS winner. (‘Fresh Look Red’ and ‘Fresh Look Yellow’ celosias were AAS winners in 2004.) This compact annual grows 12 inches tall and sports many dense, 4 inch long, golden flower plumes. ‘Fresh Look Gold’ is noted for retaining good flower color without browning out. The flowers make excellent cut flowers and can also be dried for use in dry floral arrangements. Celosia grows well in full sun and average soil but will also tolerate hot, dry conditions.
Another winning flower for 2007 is petunia ‘Opera Supreme Pink Morn’. A single plant of this wide-spreading petunia can cover an area 3 to 4 feet wide. The plants are covered all season with loads of bright, iridescent pink flowers with white throats. ‘Opera Supreme Pink Morn’ looks great in flower beds, in containers and hanging baskets, or spilling over retaining walls or terraces. Allow plenty of room for plants to spread. Petunias tolerate a range of growing conditions but will perform best when grown in slightly moist, fertile soil in full sun.
The third flower winner for 2007 is vinca ‘Pacifica Burgundy Halo’. This striking annual flower is designated as a bedding plant award winner for its outstanding performance both in greenhouse production and out in the garden. ‘Pacifica Burgundy Halo’ grows about 12 inches tall and wide. It has glossy deep green leaves and bears numerous large (2 ½ inch wide) flowers of a rich burgundy color with a white eye. Vinca performs well in garden beds and containers. This annual is very tolerant of heat and dry soil so it’s an excellent choice for sunny, dry locations.
The sole vegetable winner for 2007 is the pasilla-type pepper ‘Holy Mole’ (that last word is pronounced MO-lay and refers to mole sauce, not the burrowing rodent!). This variety bears healthy crops of narrow, 8 inch long peppers that turn reddish brown at maturity. The ripe peppers are typically dried and can be used to make rich, mildly spicy mole sauce. It takes about 85 days from transplanting in the garden for fruits to mature. This is about 1 to 2 weeks sooner than most other pasilla peppers, but Minnesota gardeners may still need to use season extenders such as high tunnels in order to fully mature the crop. Plant pepper transplants out only after soil has warmed and night temperatures stay above 50. Peppers need full sun and slightly moist, fairly fertile soil.
Seeds of these award-winners are available now in catalogs (J. W. Jung and Park Seed carry all four; other seed companies including Harris, Stokes, Johnny’s Select Seeds carry several). If you don’t have the time or facilities for indoor seed starting, look for transplants of these AAS winners at garden centers this spring.
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 55744
U of M West Central Research and Outreach Center
46352 State Highway 329
Morris, MN 56267
U of M Display and Trial Garden
Corner of Gortner and Folwell Avenue
St. Paul, MN 55108
Minnesota Landscape Arboretum
3675 Arboretum Drive
Chaska, MN 55318
Lyndale Park Gardens
4125 E. Lake Harriet Pkwy.
Minneapolis MN 55409
Photos: All-America Selections
Indoors
Keep houseplants evenly watered. 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.
If you’re keeping holiday plants, see David’s article above for tips on care.
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.
Outdoors
Winter mulch and even permanent mulch like wood chips can still be applied. Keep permanent mulch no deeper than 3 to 4 inches around trees and shrubs to allow air and water penetration.
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.
You can still apply ¼-inch mesh hardware cloth around the base of trees, especially fruit trees, to prevent vole gnawing damage.
A thousand thank-yous to Beth Jarvis and all of the folks that have contributed to this great newsletter since it was launched in 1999. I have learned many new things over the years from reading all the wonderfully informative articles. With the help of many old and new contributors I hope to continue to keep this a fun and valuable source of gardening information.
Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/.
Deb Brown will be answering a few gardening questions with Cathy Wurzer on MPR, the first Friday of the month during the fall and winter, between 8:30 and 9:00 a.m. Then in spring, she'll be back at her regular schedule, 10 a.m. the first Friday of each month. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.
For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.
If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist
Happy gardening!
Nancy Rose
Editor
REE - Horticulture
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