UW Hydrology Study Underway In Holly Collection

April 15th, 2011 by UWBG Horticulturist

Soil test pits indicated by color push pins on map

If any of you have visited the north end of our holly collection in Washington Park Arboretum recently, you probably observed what appears to be a developing wetland. As you may well imagine, standing water where we’re trying to grow healthy hollies just don’t mix very well. See Chris Watson’s post on “Spring Pruning in the Arboretum“.   Why all the standing water? Well, we don’t know.  However, thanks to a collaboration with our School of Forest Resources hydrology professor, Susan Bolton, we may soon have the answers we seek. SFR undergraduate student, Traci Amico, has taken on this investigation as her senior capstone project.  Once we know the source of all the water, we will then be able to plan a viable drainage system that will move the water away from our cherished hollies.  Below is notice for project and will also be posted at site:

  • Notice:  10 soil pits will be dug around the site and monitored on a weekly basis in an effort to determine the source of  flooding in the area.
  • Location:  UW Arboretum, Holly Garden, Lake Washington Blvd and Boyer Ave E
  • Timeframe:  April-May 2011
  • Safety:  Soil pits will be covered and marked with cones

Study Parameters:

I. Soil Pits

a) Data collected from the soil pits will assist in determining soil types and hydrology of the site.

b) After careful consideration of other monitoring processes, soil pits were chosen as the best method for the site because of they are a minimally invasive and relatively inexpensive method of data collection. The pits can be dug with a hand held spade or auger so no heavy machinery will be on the site to further compact the soils. Pits will be dug to no more than 16 inches  and 12 inches in diameter.

c) Pits will be marked with flags and securely covered with plywood to ensure the safety of humans and pets.

d) Exposing soil horizons via soil pits will allow for the visibility of water levels, to ascertain its depth and exposure soil horizons. Monitoring will be done once a week.

e) Suggestions for soil pit locations at the site are below. Google Earth imagery was used.

II. City of Seattle

a) The City of Seattle IT Department has generously offered to let me study   their GIS imagery and plans. With these I will be able to determine the locations of any buried pipes or irrigation and assess the vegetation and hydrology patterns over the years.

III. Google Earth and Aerial Images

a) Google Earth and aerial imaging are both valuable tools in assessing previous vegetation and hydrological patterns at the site due to the historical and 3-D images and ‘real time’ views provided.

Mason Bees in the Arboretum

April 13th, 2011 by UWBG Arborist, Chris Watson

With the goal of enhancing pollination efforts, several mason bee houses have been placed throughout the Arboretum.  What are mason bees?  Well, according to the provider of the pollinators, Dave Richards of JohnnyAppleBeez, LLC:

“The charming Mason Bee is a gentle, shiny blue-black metallic bee, and slightly smaller than a honey bee. They are a superior pollinator, but do not produce honey. Only 350 females are needed to pollinate an acre of apple trees rather than 25,000 honey bees.  After emerging in the spring from cocoons, these solitary bees first mate, then the female begins to forage pollen and nectar from flowers for next year’s offspring.

The Mason Bee gets its common name from their nesting habit of using mud to create protective partitions for their young when reproducing. When the female has provided a sufficient supply of food for the larva, she lays an egg and then seals the cell with a thin mud plug. She then provisions another cell, and continues in this fashion until the nesting hole is nearly full. Finally, the bee plasters a thick mud plug at the entrance to protect the offspring from predators and the weather.

They are not aggressive and they may be observed at very close range without fear of being stung, unless they are handled roughly or if trapped under clothing. In nature, the Mason Bee nests within hollow stems, woodpecker drillings, and insect holes found in trees or wood. Sometimes, there may be dense collections of individual nest holes, but these bees neither connect or share nests, nor help provision or protect each other’s young. Their short foraging range is about 100 yards from the nest. Depending on the weather and available food, activity continues for around four to six weeks and then the adults die.”

The bee houses will remain secured in trees until late June, when the new cocoons will be collected for next year.  Eight boxes are located along Arboretum Drive, Azalea Way, and Pacific Connections.  Can YOU find all of them?

 

 

Spring Pruning at the Arboretum

March 30th, 2011 by UWBG Arborist, Chris Watson

Recent Arboretum visitors may have noticed some unusual pruning, specifically in our Holly and Camellia collections.  The camellia specimens, located near the Lookout parking lot, will be re-propagated and planted in a different location to make space for the Pacific Connections New Zealand focal forest.  Large heading cuts were made to induce new epicormic growth, or watersprouts, which are ideal for propagation.  Cuttings for propagation will be taken later this summer.

The hollies can be found along the south side of Boyer Ave. near Lake Washington Blvd.  These hollies have been struggling since they were transplanted several years ago.  While not quite as radical as the camellia pruning, some might be surprised to see this style of pruning in the Arboretum, myself included!  However, in his book Hollies: The Genus Ilex, Fred Galle refers to a style of pruning called “hatracking or coatracking…best done in early spring, so new growth begins to cover the bare stems the first season…In two years the plants will show no signs of being severely pruned.”  We hope that this harsh pruning will induce a flush of new growth that rejuvenates these declining specimens.  Stay tuned for updates.

Cherry Blossom Season is Here!

March 25th, 2011 by UWBG Horticulturist

Most visitors experiencing the beauty of our historic Azalea Way flowering cherries from now through May probably have no idea of how intensive maintaining their health and prolonging their longevity truly is for the UW Botanic Gardens horticulture staff.   Just ask our Integrated Pest manager, Ryan Garrison. Ryan with staff support spends many a day throughout the year monitoring and controlling the numerous diseases and insect pests our 175 plus cherries are prone to suffer from. Our rainy climate doesn’t help one bit either, especially when dealing with our most notable disease during blossom time;  a fungus known as Cherry Blossom Brown Rot. Yucko!  The good news is any new cherries we plant need to show a reasonable level of resistance. The not so good news is many of our older earlier bloomers, the ones extremely susceptible to the brown rot fungus,  need to be protected with fungicide applications during their bloom period.  As with all of our pest issues, we start with cultural and mechanical control efforts before resorting to chemical controls. The following Integrated Pest management (IPM) program discusses our best management practices for the control of blossom brown rot.  If you are interested in planting cherries for your home garden, I’ve included a list of cherries recommended for our PNW climate, all have good to excellent resistance to blossom brown rot.

Cherry Blossom Brown Rot - causal fungal agent known as Monolinia fructicola. The fungus overwinters on infected twigs and dried fruit on the tree or ground.  The fungal spores are spread in the spring by wind and rain through the blossoms, causing twig dieback.  As part of the UWBG IPM program, moving toward our goal of eliminating the use of all synthetic pesticides is our ultimate goal.

IPM relies on many strategies to manage plant health care. 

  • Proper ID of the pest and its life cycle
  • Regular monitoring of the plants
  • The use of physical, mechanical, cultural, and biological controls
  • Chemical controls used as a last resort*
  • Least toxic chemicals used

* All spray applications are in compliance with WSDA pesticide regulations.  Sign postings are located at all entrances and Graham Visitor Center. Spray applications are scheduled based on timing and weather. We do our best to apply when public are not present. For more information, pls contact, David Zuckerman at 206-543-8008 or dzman@uw.edu

The cherries are pruned in early fall  to remove infected twigs and improve air circulation.  Tree rings are given a fresh coat of mulch in the fall to bury any infected plant material that may be on the ground.  In our Cherry Replacement program we are only using cultivars that are resistant to Blossom Brown Rot.

Cherries recommended for the PNW:

    • Prunus ‘Berry Cascade Snow’
    • Prunus ‘Kwanzan’ syn. ‘Sekiyama’
    • Prunus ‘Pink Flair®’
    • Prunus ‘Royal Burgundy’
    • Prunus ‘Shirofugen’
    • Prunus ‘Shirotae’
    • Prunus ‘Snow Goose’
    • Prunus subhirtella var. ascendens
    • Prunus x yedoensis ‘Shidare Yoshino’

 

 

Sonic Tomography at the Arboretum

March 18th, 2011 by UWBG Arborist, Chris Watson

The University of Washington Botanic Gardens would like to thank Tree Solutions, Inc. for bringing the latest technology in tree risk assessment to the Washington Park Arboretum.  Tree Solutions assessed a large western hemlock (Tsuga heterophylla) using sonic tomography, a device which measures sound waves to detect decay and other abnormalities in wood.

Assessing the risk associated with trees is a vital component to maintaining the urban forest.  Visually assessing a tree can often give more than enough information.  However, what cannot be seen can yield valuable information to the risk assessor or manager.

It is normal for trees that appear healthy to have decay inside the trunk and limbs.  It is the extent of this decay, along with the overall vitality of the tree that determines management (pruning, cabling, removal).  Traditional methods of assessing internal decay include sounding the tree with a mallet, increment borer, and drilling.  A more sophisticated method is the resistograph, which determines the decay extent using a very fine drill bit and produces a printed record.

Among the very latest technology is the minimally invasive procedure (i.e. no drilling!), sonic tomography.  Sound waves sent through the tree are measured by sensors placed around the assessed part, which feed into a computer.   The computer analyzes the input producing a color image which accurately shows healthy wood and decayed wood.  This detailed information greatly helps in determining management of the Arboretum main attraction…the trees!

Hollies in Good Condition After Relocation

March 15th, 2011 by Tech Librarian, Tracy Mehlin
Ilex opaca in WPAA mature Ilex opaca tree that stayed behind in the Pacific Connections Garden 

UW Botanic Gardens Collection Manager, Randall Hitchin, reports the majority of the hollies transplanted in 1999 are in good or excellent condition. More than 150 plants were moved in order to make room for the new Pacific Connection Garden.

The Arboretum has one of the most diverse holly collections in the United States. The collection grows on the west side of Lake Washington Blvd just south of Boyer Ave.

2010 Holly Collection Summary for the Washington Park Arboretum

Winter Plant Protection in Pacific Connections Gardens

November 22nd, 2010 by UWBG Horticulturist

"Straw Tepees" in New Zealand entry garden

No, aliens haven’t invaded the arboretum. The “straw tepees” (left), as Kyle Henegar, PCG gardener, aptly coins them, are to protect the newly planted Phormiums and other marginally hardy New Zealand plants make it through this cold spell that’s hit Seattle. It just wouldn’t seem fair to let these plants try to make it on their own since they were just planted late last summer and have yet to get their roots established.

The new Chilean Gateway garden also has several box structures dotted along the rockery hillside (bottom right). These wooden frames enveloped w/ shade cloth are protecting our new Chilean wine palms that are indeed cold sensitive.

Box over palm

Sundstrom, Gateway contractor, has also treated the palm’s crowns w/ a copper-based pesticide, to help inhibit the colonization of bacteria and fungal crown rots. If you look inside the structures, you’ll notice straw has been used to blanket the trunks and crowns as well.

Let’s all hope that these extraordinary winter protection measures pay off. We won’t know for sure until late spring or even early summer in some cases. And no, you needn’t worry about alien invasions in the arboretum.

Cherry Pruning Time

October 8th, 2010 by UWBG Horticulturist

Our horticulture staff will begin pruning our cherry collection, mostly along Azalea Way, next week. October is our window to prune based on the life-cycle of the insect pest, Cherry Bark Tortrix -it’s not flying around seeking easy entry portals like fresh pruning wounds now. Most of our pruning focuses on  large dead branches, as well as, unwanted basal suckers below graft unions. We just don’t have the staff to detail out all the small dead twiggy growth from years of brown rot infestations. We do mulch our cherries which helps decrease amount of fungal spores to reinfect next year’s blossoms.

Also, our tree crew will be removing 7 decrepit – brown rot and decay riddled, poor health specimens. 6 are Prunus subhirtella cvs. (the most susceptible to brown rot) and one is a Prunus sargentii w/ significant crown die-back. We may decide to replant if the sites are suitable w/ brown rot resistant cultivars in the future.

Garden Loosestrife – Spray Application Scheduled 9/22

September 14th, 2010 by UWBG Horticulturist

UWBG IPM staff will be out on Union Bay, Wednesday, September 22nd, w/ spray contractor NW Aquatic Eco-Systems. All canoe landings and shoreline trailheads will be posted. This is the second of  two  follow-up spray applications in our effort to control the class A noxious weed, Garden Loosestrife.

Holly Garden Project Notice and News

August 26th, 2010 by UWBG Horticulturist

Eurasian berms are located at far right - in pink

 

September through October is our window of opportunity before fall rains begin to commence development and improvement work in the Holly collection.  Scope of work during this period will focus primarily on construction  of  the southernmost Eurasian clade berm located at the north end (near Boyer Ave). See photo of Iain Robertson’s conceptual Holly collection plan – Eurasian clade berms are pink. 

  • In-house tree removals  – 4 small undesirable Bigleaf maples and 4 maple stump sprouts
  • Contract tree removals  – 6 cottonwoods and 1 Western red cedar
  • Also, removal of 4 collection hollies in very poor condition in existing Eurasian berms

During this project work, area will be cordoned off to public and if needed, pedestrian detours will be established. 

Project info will be posted at work site and at the Graham Visitors Center. 

Beginning in late October 2010, regional Qwest corp, will begin a new partnership with UW Botanic Gardens and Seattle City Parks and Recreation. Under the guidance and training of UWBG horticulture staff, Qwest  volunteers, known as Pioneers, will ultimately “adopt” the Holly garden for a year in all facets of horticulture care and maintenance. Initial tasks will focus on: 

  • Finishing southernmost Eurasian clade berm construction if weather permits – grubbing, grading, soil work
  • Modification of northernmost Eurasian clade berm – adding more soil to raise profile and improve drainage
  • Plant and care of several new holly collections, mostly Eurasian clade members
  • General maintenance (weeding, mulching and edging) of the entire Holly garden, including native restoration sites

We look forward to our new partnership with Qwest Pioneers and a marked improvement of our Holly garden.A project sign will be installed on-site in the next few weeks by Seattle City Parks and Recreation.