The Smithsonian Gardens Tree Collection currently consists of over 1,850 trees, approximately 1,400 of which are located on the downtown Washington, D.C. and Anacostia campuses. These trees add beauty to our grounds, and they offer myriad environmental and health-related benefits. Unfortunately, it seems that trees are constantly under attack by a host of problems, ranging from severe climate, to native and exotic pests and diseases, to damage from construction and development projects, to the tough urban environment in which they grow. Once these plants become stressed, it’s more likely that they will suffer due to one or more of these issues. In addition, as trees grow, certain structural defects can develop which may cause problems in the future, especially when severe weather events can exploit the inherent weaknesses in these defects.
For these reasons, we at Smithsonian Gardens take a proactive, rather than reactive, approach to caring for these green assets. Oftentimes, defects, cultural stressors, or insect and disease infestations that have gone unnoticed for a time can be difficult, if not impossible, to reverse. Therefore, a thorough health and structure assessment of these trees was completed at the end of 2014. This assessment consisted of a top-to-bottom, 360 degree visual evaluation of each tree. All defects and other potential issues were noted and assigned a rating based on the severity of the condition observed.
What we had at the end of the evaluations was a complete list of trees, their problems (if they had any), and recommendations for correcting anything of concern. Based on the ranking system, we now have an organized and detailed list of what maintenance and tree care work is needed, with a clear indication of where we need to start. This has enabled Smithsonian Gardens to find and fix issues before they become more serious, and gives us the ability to be proactive with our tree management. It also gives us a better idea of how to budget for upcoming maintenance needs. Prevention is the best medicine, and any time we can find and correct an issue before it becomes serious it allows us to keep our trees happy and healthy for many years to come.
-Greg Huse, Smithsonian Gardens Arborist and Tree Collection Manager
Orchids make up one of the largest (or THE largest, depending on whom you ask) plant families with over 25,000 species. In such a large family, there is bound to be incredible variety in size, shape and color. This week the small blooms caught my eye more than anything else. It is astonishing to see such vivid coloration and detail in flowers that are no bigger than my thumbnail!
Stenosarcos Vanguard is a stunning hybrid of the two Latin American species Stenorrhynchos albidomaculatum and Sarcoglottis acaulis. This terrestrial beauty has uniquely variegated leaves and its tall, red inflorescences boast numerous small blooms that are just begging for a closer look.
The flowers of Vanda aurantiaca are even smaller than those of the Stenosarcos, but no less impressive. The shocking yellow-orange flowers pack quite a visual punch bundled together on racemose inflorescences, one of which you can see below.
One of the most striking blooms that caught my attention this week foreshadows an explosion of color. The tiny purple flower seen here comes from Isabelia pulchella, a miniature epiphytic species with long, dangling rhizomes. Pseudobulbs grow spaced along the rhizome and each supports exactly one grassy leaf and a single-flowered inflorescence. This orchid will sport hundreds of these purple gems when the rest of the plant bursts into bloom.
There is always something blooming in the Smithsonian Gardens Orchid Collection. Stay connected with us to see more plants from the collection that will amaze you with their diversity!
-Julie R., Living Collections Specialist
Winter is prime time for beautiful blooms in the Smithsonian Gardens Orchid Collection. The greenhouses are bursting with flowers, a welcome sight after all the gloomy weather we’ve been having in the DMV lately.
Recently, I have been appreciating the variety of pink color found in many of the hybrid orchids in the collection. The pink of Oncidium Tsiku Marguerite ‘HOF #3’ is subtle and understated, but this orchid makes itself known through its powerful aroma, a somewhat powdery sweet scent. These tiny flowers pack quite a punch (albeit one that I would return for day after day).
Farther down the greenhouse, the vivid orange-pink of Rhyncholaeliocattleya Pumpkin Mist is enough to make one stop and smell the flowers. Literally. Cattleya hybrids are famous for their strong fragrance, many of them such as this one, have scents reminiscent of pansies or hyacinths.
While Phalaenopsis orchids aren’t known for their fragrance, they are known for their fantastic, showy hybrid crosses. The patterns on the flowers of many novelty Phalaenopsis hybrids are so unique; this one a dark magenta color radiating like a thick bronchial tree into a light pink border. Even if these patterns are useless for attracting pollinators, they do a marvelous job of drawing in their human audience.
Smithsonian Gardens Orchids are constantly in bloom. Stay connected with us to see more plants from the collection that will brighten the dreariest of winter days!
-Julie R., Living Collections Specialist
In 2012, the Smithsonian Gardens Green Team developed an Eastern Bluebird Trail at our greenhouse complex in Suitland, Maryland. The trail of ten paired nest boxes was designed to support and expand the year-round resident Eastern Bluebird population. By the end of the 2013 nest season, the bluebird population had expanded to about thirty birds.
What happened in 2014? We began monitoring the trail in March, looking for the first signs of nesting behavior. The monitoring continued through July and in that time, no Eastern Bluebirds have been seen at or around the greenhouse complex. We believe the resident population migrated to another location due to a harsh winter of repeated deep Arctic cold blasts starting in late November and persisting through March. In addition to the cold, we believe the bluebirds did not have enough food to support their population.
Bluebirds rely on fruit for more than thirty percent of their diet. In the winter, when insects are scarce, they depend on persistent fruits more than at any other time of year. The SG Green Team is committed to planting more native tree and shrub species around the facility to provide a sustainable winter habitat for the birds. Planting trees and shrubs not only provides food for birds but also provides shelter from harsh winds and cold temperatures.
-Sarah Hedean, SG Green Team Member
This summer, many exciting things happened with the Smithsonian Gardens Orchid Collection (SGOC). Not only are the greenhouses getting a good cleaning and reorganization, but Smithsonian Gardens is seeing significant additions to its species collection. In March, SGOC’s tropical species became an accredited collection with the North American Plant Collections Consortium. As you may recall from reading about the accreditation on the blog this past spring, this designation comes with a responsibility to continually improve collections management practices and species representation.
In June, Smithsonian Gardens’ terrestrial orchids received quite a boost in numbers. Collection managers Tom Mirenda and Sarah Hedean made a trip to a local nursery to purchase Paphiopedilums and Phragmipediums. They found many valuable additions for the collection, including a blooming-size Phragmipedium kovachii and several associated hybrids. We will hopefully see these spectacular kovachii flowers within a year. Additional Phragmipediums were obtained from another nursery, including Phragmipedium brasiliense, Phragmipedium boisserianum and Phragmipedium sargentianum. All three species are new to the collection.
June was a very busy month for accessions. At the end of the month, Tom flew out to California to speak at the request of Orchid Digest and during his trip, was able to stop by a local nursery to purchase almost sixty additional plants for the collection. This purchase includes a number of new species that address collection gaps identified by SGOC’s 2013 benchmarking study.
In August, four species of Pterostylis in the form of bulbs were donated to the collection. These propagules are from orchids that won the highest possible score from the American Orchid Society for specimen plants (99 points). Since these are colony-forming species, these propagules will be clones of the highly-awarded individuals. In this same donation we also received several bulbs of a Diuris hybrid. Diuris is commonly known as the Donkey Orchid due to the fact that two of the petals emerge from the top of the flower like donkey ears.
This fall, SGOC received an influx of Cattleya hybrids in anticipation of the 2015 Orchid Exhibit and the San Diego Zoo Botanical Collection sent Smithsonian Gardens a Paphiopedilum tigrinum in exchange for one of our Psychopsis hybrids.
It is very exciting to see significant progress made this yeat towards achieving our goal to improve the tropical species collection. Hopefully the momentum will continue into 2015 and beyond!
- Julie Rotramel, Living Collections Contractor
Ever heard of the pawpaw tree? Ever tasted its fruit? Did you even know it had fruit? Though it may not have the name recognition of an apple or a peach tree, pawpaw trees have a long and important history in the United States. In 1541, Hernando de Soto observed Mississippi Valley Native Americans growing pawpaws and eating the fruit. According to scientist Neal Peterson, the Spanish mistakenly named the pawpaw fruit “papaya.” Spanish explorers selected this name because they observed pawpaw fruit to have a similar green skin and orange flesh to a papaya. Overtime, the English language transformed the fruit and tree species name from papaya to pawpaw (Asimina triloba).
According to James A. Little in his 1905 A Treatise on the Pawpaw, pawpaw fruit helped sustain Native Americans and early American settlers in times of harvest failure. Little wrote that pawpaw trees needed little maintenance in order to survive in the wild, unlike apple, pear, or peach trees. Thanks to its resilience, Native Americans and early pioneers enjoyed pawpaw fruit as a dependable source of fiber and nourishment. Even members of the Lewis and Clarke Expedition survived on pawpaw fruit during their long journey west in 1804-1806.
Found between Georgia and Northern Michigan, pawpaws extend across eastern portions of the United States. Unlike the tropical members of the Annonaceae family to which it belongs, pawpaw trees thrive in harsh conditions of snow and ice. Despite this resilience, pawpaws still struggle to reproduce. Scientists believe the tree is ineffective at attracting flies and beetles to pollinate its flowers, thus creating challenges for reproduction.
The pawpaw tree produces a very nutritious and delicious fruit, which is actually a berry. The pawpaw berry is also called a “custard apple” and is said to taste like a mix between a banana and a pear, with a hint of vanilla. The name custard apple derives from the creamy texture of the fruit.
Smithsonian Gardens currently has seventeen pawpaw trees in its Tree Collection. They can be found in the Native Landscape garden at the National Museum of the American Indian, the Butterfly Habitat Garden adjacent to the National Museum of Natural History, and the National Air and Space Museum.
Next time you stop by one of the Smithsonian gardens keep an eye out for this beautiful tree with a deliciously-interesting past.
-Jessica Brode, Archives of American Gardens intern
As we gaze around at the beautiful autumn colors that our trees are showing us, we’re trying not to think about the arrival of the cold and snowy weather of winter. However, arrive it will, and now is the time to prepare your trees for those coming winter months. Although all trees are potentially susceptible to winter injury, young and/or thin-barked, and broadleaf evergreen trees require the most preparation.
Excessively cold temperatures, wind, and quick temperature changes can cause drying, browning, and death of evergreen foliage. This problem is most prevalent on broadleaf evergreens such as rhododendrons, laurels, boxwoods, and hollies. To help prevent this damage, construct a barrier of heavy burlap, like a fence, to block drying winds from their prevailing direction. If the entirety of the plant is exposed, loosely wrap it in burlap. In either case, be sure to leave the top of the plant exposed so light and air penetration can still occur. In addition, it is important to keep watering your trees up until the time of the first hard frost. A 4-6 inch layer of mulch over the root zone will also help the soil retain warmth and moisture. (Remember not to pile the mulch up against the trunk of the tree.)
Another issue of concern, which is also caused by rapidly fluctuating temperatures, is sunscald. This occurs when the sun has warmed the trunk of the tree, and then that trunk is rapidly cooled upon sudden shading from a cloud, etc. This condition results in elongated, dried and cracked areas of dead bark. This can be prevented by wrapping the trunk with commercial tree wrap (available at most home and garden centers) or other light-colored material. This will reflect sunlight and keep the bark at a more consistent temperature. The wrap should be placed on the tree in the fall and removed in the spring, after the last frost.
Broadleaf evergreen foliage damage and frost cracks are influenced by many factors, including plant species, location, drainage, natural protection, and how well established a plant is in the landscape. There is no specific temperature at which damage occurs, but if the forecast calls for temperatures below the average seasonal low (29-33°F for Washington, D.C.), it is best to utilize the protection methods outlined above.
Tree branches can be prone to breakage from heaving snow and ice loads and by strong winds. Weakly attached, overextended and broken limbs should be pruned. Trees with an upright form, such as juniper, arborvitae, and clump birch, can be wrapped in burlap, or held together by wrapping the branches collectively with twine or rope. Any wrapping material should be removed in the spring.
When natural food sources grow scarce in the winter, rodents may feed on the young bark and cambial tissue of trees. Plastic tree guards or a cylinder of ¼” wire mesh placed around the trunks of young trees will help prevent this damage. Be sure to remove these guards once the spring has come so the tree does not wind up growing into them.
Trees possess an extraordinary ability to withstand severe winter weather, with some being more hearty than others. However, with proper care and attention, your trees should come through the winter ready to show off their new flowers and foliage for spring.
-Greg Huse, Smithsonian Gardens Arborist & Tree Collection Manager