Archive for street trees

Birch Trees Going Going Gone

Birch trees going going gone

Another birch tree marked for removal by the City of Portland due to bronze birch borer.

Birch trees marked for removal by the City of Portland due to bronze birch borer.

In 2010 Kym Pokorny, my favorite garden writer, warned that our graceful white bark birch trees might become a tree of the past in Portland.    Fast forward to today.  Boy was she right!!  It seems to me as I look back over these past years that the birches in the subdivisions died first.  Many developers, builders and home owners picked the Himalayan White Birch also called Jacquemontii, for its crisp white bark and over planted them.   In 2009 I was working with landscape design clients in a Vancouver neighborhood.  They had already had 2 birch trees removed and we made a replacement plan for the third as part of the Landscape Design in a Day.  Their neighborhood had already removed over 200 birches.  Their developer had used them extensively.  Back in the 1980’s the Himalayan White Birch was touted as the new success story because it had been hybridized to repel the Bronze Birch Borer.  Over time however the bronze borer changed its preferences and became attracted to the available and over planted Himalayan or White Birch.  It makes sense from an evolution perspective; why not change to fit the food that is available?  Smart bug!!!

Fixed up close view

Himalayan White Birch used to repel birch borer.

Recently I have noticed the dreaded yellow tape of death tied around birch trees in the city.  I create my Landscape Design in a Day drawings on site with my clients so I am in every conceivable neighborhood.  The Bronze Birch Borer is now in North Portland to SE Portland, not just the suburbs.

These days when I have a client who has a healthy looking birch I give them the current research and bad news.  From what I have read there isn’t a whole lot of good news.   I often include in their design a potential replacement tree for when, not if, their tree is devastated by the Birch Bronze Borer.  It’s shocking and pretty sad for them to hear that they will probably witness the demise of their tree especially when it looks just fine.

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Heritage River Birch in winter.

If you have a birch tree that is thriving consider starting to irrigate it if you haven’t already. You might start by deep watering it every two weeks. Under no circumstances should you water your tree every day – that is not helpful  (see my watering tips blog).   There are chemical protections that you can apply to your tree before it becomes infected that will typically keep it from getting the borer.  General Tree Service is one company who provides this  service.    Sometimes the tree can be saved  if you can catch the infestation at the very beginning but you will need to apply the pesticide every year.  Another important issue to think about it this:  The product is a systemic pesticide.  Many people refuse to use any systemic pesticide because some can kill honey bees.  Birch trees are wind pollinated not bee pollinated and so the systemic should not theoretically affect honeybees.   If you have flowering plants of any kind under or near the birch those plants will uptake the pesticide and that can harm bees.  This protection for your birch is contrary to protecting bees.  I guess you could take out your hostas or other flowering plants and put in sword ferns.  In short, if you love your tree, start taking care of it.  The first trees that died seem to me to have been neglected trees in full sun and in areas where there were too many birch trees so the borers could move from one tree to the next door neighbors tree.

Weeping Katsura is my go to birch replacement now since borers have killed so many birches.

Weeping Katsura is my go to birch replacement now since borers have killed so many birches.

What to look for:  The first signs are yellowing foliage in the top of the tree.  As the insect infestation continues, small branches and tips die.  It moves on into the larger branches.  Declining to the point of death usually takes several years but remember last years horrid, hot and nasty summer?  There were trees who seemed to get the borer early and by the end of the summer, the trees were gone.   There are other signs of borer; ridges in a lightning pattern and a distinctive D shaped hole in the bark.  There can be a kind of stain coming from the hole, a sort of reddish liquid which looks as bad as it sounds………Is my tree bleeding?  So this is not a happy blog but there are some great trees to consider for replacement.

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Katsura tree with beautiful fall color.

New resistant varieties;   I am hesitant to trust that new resistant white barked birch varieties will stay resistant since the Jacquemontii/Himalayan did not stay resistant.  When I have a client who loves birch trees I offer the River Birch which has a brown peeling  bark and typical birch leaves.   Alternatively my favorite replacement  for birch trees is the Katsura tree also called Cercidiphyllum.  The Katsura has the graceful shape somewhat reminiscent of a birch tree and since it is not related to birch I am not worried about Borers.  I know that the trees I place in a home landscape may be removed for capricious reasons by the next homeowners but selecting trees that have the best chance of becoming mature old specimens in their neighborhood is my chance to contribute not only to my clients well being but for my city and region.  Keeping up to date up on the best trees to use and keeping my selection diverse will make the best urban forest for the future.

Katsura 'Red Fox' is a smaller tree that is getting used in irrigated parking strips.

Katsura ‘Red Fox’ is a smaller tree that is getting used in irrigated parking strips.

White birch trees that have been planted in part shade, in good soil that drains well and that get irrigation may continue to survive.  Another bit of advice from Kym Pokorny’s article is to mulch over the shallow roots of your birch tree.  This provides some protection from heat and also from physically damaging the surface roots.  I’ve been told by an arborist in the past not to put more than 2 inches of mulch over  roots.  The best person to ask about these fine points of tree care is an ISA Certified Arborist.

Katsura 'Red Fox' has unique red foliage.

Katsura ‘Red Fox’ has unique red foliage.

I came across a lovely white birch tree just the other day in the Buckman neighborhood and gave my new client, who had just purchased the home, some information on how to care for the tree. The tree doesn’t seem to be infected.  Some birch trees that are individuals, seed propagated instead of cutting, may have some unique genetic protection and so we can only hope that some of these individual trees will remain to grace our landscapes and homes.

 

 

 

Diversity of Dogwoods Part II

Portland Landscape Designer Appreciates Diversity of Dogwood Trees

The diversity of dogwoods is well illustrated by these two trees:  Cornus Kousa ‘Summer Gold’ and Cornus Controversa ‘June Snow’.

Summer Gold dogwood

Bright cream flowers are backed by colorful variegation of ‘Summer Gold’ dogwood. Photo courtesy of Heritage Seedlings

Korean Dogwood ‘Summer Gold’

I love ‘Summer Gold’ partially because it’s so different from other dogwoods.   ‘Summer Gold’ has narrow bright green and gold leaves and an upright narrow shape.  The shape fits into urban settings much better than a round headed typical dogwood.

Traditional dogwoods (Cornus Florida and Cornus Kousa) have a wide oval solid green leaf and a  20′ or more wide round canopy.   ‘Summer Gold’ was created by local Crispin Silva who is a delight.  His curiosity and enthusiasm about plants has inspired many people in Portland including me. People here refer to his plants as “Crispin’s Creations”.

‘June Snow’ can be the single tree in your backyard because she has it all, grace, fall color, and an amazing floral display.

‘June Snow’ Dogwood matures at 30′ tall and spreads to 40′ wide. She has an arching shape and while bigger than typical dogwoods She has the most graceful silhouette even in winter.  I use her to create light shade for medium to medium small landscapes.  Too big for your typical row house back yard that is only 20′ wide, with another ten feet she can be the single beloved tree.  She was introduced by J. Frank Schmidt Company also near Portland, Oregon.

Her branch structure is incredibly graceful and open.

Cornus 'June Snow'

‘June Snow’ dogwood at Portland’s Legacy-Emanuel Hospital in The Children’s Garden.

When she flowers in June these flat topped clusters (which often exceed 6 inches) seem to float above the foliage.  The fall color on ‘June Snow’ can compete with any dogwood. The color show starts with orange yellows and moves into intense purple red and purple as fall deepens.  The fruit that develops from the flower clusters are quite tiny and not messy.  The local birds will eat them.

Studying trees is what Portland landscape designers do so we can bring you the best choices.  Ok and we are geeky about plants.   Read more about dogwood trees….. Diversity of Dogwoods Part 1

 

 

 

 

Diversity of Dogwoods Part I

Cornus Kousa 'Satomi' at Joy Creek Nursery.

Cornus Kousa ‘Satomi‘ at Joy Creek Nursery.

Diversity of Dogwoods – Part I

Dogwoods are a very large family.  There are twiggy shrub dogwoods whose hot colored stems light up the winter landscape.  There is a dogwood who blooms in March with yellow flowers and makes an edible fruit.  There are semi evergreen dogwoods we are experimenting with here in Portland.  This is the kind of knowledge homeowners need their designers to be up to date on.  When a client asks me for a dogwood I know its the visual and emotional impact of the flowers they are thinking of.  Designers think through the details to find the right variety for the clients size of yard and environment so our clients don’t have to.  Landscapes come in all different sizes and environments and now so do Dogwoods.

Plant designers have been busy improving our old-fashioned dogwood tree into a garden designers dream tree. Our old dogwood varieties have problems that plant designers have been working on for 40 years.

Cornus-Kousa 'Satomi' Intense pink flowers. Photo by Randall C. Smith, courtesy of Great Plant Picks

Cornus Kousa ‘Satomi’  Intense pink flowers.  New on the scene, ‘Little Ruby’  is a deeper pink. Photo by Randall C. Smith, courtesy of Great Plant Picks

They are improving drought tolerance, disease resistance (okay not sexy but important!)  and cold hardiness.  They’ve created new shapes that fit better into the urban environment.

What is sexy or desirable are the improvements made to the flowers.  Let’s admit it, where dogwoods are concerned,  we want even pinker flowers.   Everyone wants more color than nature supplies on her own. There are darker shades of more intense pink red.

Cornus Kousa 'Venus' has large dogwood flowers

Cornus Kousa ‘Venus’ has large white flowers which are 6 to 7 inches across.

Varieties such as ‘Little Ruby’  showcase the new strong colors.   ‘Little Ruby’ is wider than tall.  She is  plump and round headed and can be used in the landscape as a shrub or small tree.

Another new variety is called ‘Starlight’.  This cross is from our own native Pacific Northwest Dogwood;  the shape is upright and more narrow.  It works for your small yard or as a street tree. There’s a beautiful ‘Starlight’ in the courtyard of the Edith Green federal building in downtown Portland as an example of a tree perfect for urban life.

Cornus Kousa 'Starlight' dogwood

‘Starlight’ dogwood is a cross from our Pacific Northwest native dogwood. The narrow shape is perfect for urban life. http://landscapeplants.oregonstate.edu/plants/cornus-starlight

 

‘Venus’ features ginormus white flowers which are 6″-7″ across.  Like ‘Starlight’ they produce little to no  fruit unlike the many Korean dogwoods hybridized and sold in the last 15 years.  In fact even Friends of Trees offer messy Korean dogwoods.  I confess I make a TSKK TSKK when I see the huge mess they make on the sidewalks. In the fall they drop a large raspberry colored fruit.  Friends of Trees is a fabulous organization and many clients have been happy to purchase an inexpensive tree and learn how to care for their tree.  I would use the fruitless varieties near walkways and for small yards and save the old fashioned fruiting types for large properties.