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Archive for street trees

Protecting Our Portland Birch Trees from Bronze Birch Borer

Protecting Our Portland Birch Trees from Bronze Birch Borer

 NE Portland 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.

Birch Trees Dying from Bronze Birch Borer

Many developers, builders and home owners picked the Himalayan White Birch (also called Jacquemontii,) for its crisply white bark and over planted them. They even planted them in parking strips with no irrigation, in full hot sun, which is not a good place for a birch. My Vancouver client’s neighborhood had over 200 mature infected trees removed. They had already lost 2 birch trees and I made tree replacement suggestions as part of their Landscape Design in a Day.

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 (BBB). At that time I was a student learning about trees at a local community college. The European Weeping White Birch had been decimated by the BBB so everyone was very excited about the new Himalayan White Birch. Over the next 20 years, the bronze borer changed its preferences and became attracted to the over planted Himalayan White Birch. It makes sense from an evolution perspective; why not change to fit the food that is available?  Smart bug!!!

City of Portland has tagged this borer damaged birch tree for removal

30 years ago Himalayan White Birch was used because it repelled Bronze 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 so I am in every conceivable neighborhood.  The Bronze Birch Borer is now all over Portland and has spread south to Klamath Falls.

Today when I see my client has a birch tree, I give them the current research and it’s mostly bad news. I often include in their design a potential replacement tree for when, not if, their tree is devastated by the Birch Bronze Borer.

River Birch (Betulus Nigra) is a safe replacement tree - Bronze birch borer does not feed on this birch tree.

Heritage River Birch in winter. River Birch (Betulus Nigra) is a safe replacement tree – Bronze birch borer does not feed on this birch tree.

Protecting Your Portland Birch Tree

My research says watering your trees regularly before they are infected is a huge step toward preventing the disease. If you have a birch tree that is thriving or only has minimal borer damage, consider starting to irrigate it ASAP. Start by deep watering it every week to two weeks starting in early summer into mid to late fall.  Don’t let your tree get stressed. (Deep water is a long slow soak with your hose.) Under no circumstances should you water your tree every day – that is not helpful.  (See my watering tips blog).

Pesticide treatments

I’m also reading that more people are using a chemical treatment (which will help your tree) than they were initially. I’m not very happy about that because the treatments will harm bees. They are mostly drenches that are systemics (bad for bees) or injections done by tree services which are also systemic in nature (and so bad for bees). Apparently the timing of the treatment and how it is done can make it less lethal to bees but isn’t this backward of  saving the bees and therefore our food supply? If it were my tree, given my very strong feelings about protecting bees, I would try watering deeply and regularly and not treat the tree with pesticides. If the tree is too far gone I would have it removed, grieve and plant a new tree that is resistant to disease and insects and prefers little summer water.

Weeping Katsura tree has similar texture to Birch

Katsura tree at Lan Su Chinese Garden in Portland, Oregon

In short, if you love your tree, start taking care of it. The first trees that died were neglected, poorly sited and in neighborhoods chock full of white barked birch trees.

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

Weeping Katsura in one of my clients gardens in Willamette Heights.

Signs of Bronze Birch Borer

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. 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 holes, a sort of reddish liquid which looks as bad as it sounds.

Cercidiphyllum_japonicum, Katsura tree

Katsura tree with beautiful fall color.

New Resistant Varieties-Maybe

I am hesitant to trust that new resistant white barked birch varieties will stay resistant if we over plant them as we did the Jacquemontii/Himalayan white birch.  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 with heart shaped leaves that flutter in the breeze.  I feel it is a safer choice since it is not related to birch at all but alas no white bark!

Selecting trees that have the best chance to become mature old trees is my way to contribute to my clients and our community. Keeping up to date on the best trees to use and keeping my selection diverse will make the best urban forest for the future.

Kym Pokorny, (now writing for OSU’s Extension Service),  says these are good replacement choices;  ‘Heritage’ river birch (Betula nigra ‘Heritage’) and ‘Whitespire Senior’ gray birch (Betula populifolia ‘Whitespire Senior,’ which has the whitest bark of the replacement tree ideas.  I suspect if we over plant these borer resistant birch trees, the borer will change its tastes to the available food so the best thing to do is plant lots of different trees.

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.

I came across a lovely old 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 seems untouched by borer and is situated where it gets some afternoon shade.  He will start to summer irrigate.  Perhaps some birch trees are unique individuals because they were grown from seed and this unique genetic combo may cause them to be unattractive to the BBB. We can only hope that some of these remaining individual trees, if irrigated, will remain to grace our landscapes and homes.  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. Boy was she right!!

 

 

Diversity of Dogwoods Part II

Portland Landscape Designer Appreciates Diversity of Dogwood Trees

Overlook neighborhood has Dogwood 'June Snow' in parking strip - close up of flower.

We recommend this 30′ wide tree for back yard or front yards not parking strips but here it is doing well in a parking strip in Overlook neighborhood of North Portland.

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

'Summer Gold' Dogwood in Flower

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

Colorful Summer Privacy Tree for Small Properties – 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.  The foliage will be a delight from spring into fall and this tree is a narrow vase shape perfect to put between your patio and the neighbors to achieve attractive  privacy.

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”.

Elegant Branch Structure Cornus Controversa ‘June Snow’ Perfect Light Shade Tree

Overlook neighborhood has Dogwood 'June Snow' in parking strip - close up of flower.

The flowers of ‘June Snow’ giant dogwood float above the graceful branches in Overlook neighborhood.

‘June Snow’ can be the single tree in your  small city 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 and for a shade tree she is typically limbed up so it is easy to walk and play under this tree.

Cornus 'June Snow' fall color in NW Portland

The fall color of ‘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

Cornus Controversa 'June Snow' as a border tree in NW Portland

More beautiful branch structure of ‘June Snow’ Dogwood. This tree used for a border keeps its’ lower branches. (ANLD Garden Tour)

 

 

 

 

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.

Spring Flowers

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. Picture from Pat Breen Oregon State University.

 

‘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.

‘Hedgerow’s Gold’ brightening up a shady area with Japanese Forest Grass as a ground cover to nicely echo the color.

Bright Summer Foliage

‘Hedgerows Gold’ grown for its gorgeous variegated foliage. This is a very easy shrub to grow, once it is established it can take some benign neglect. Grow it for the foliage first, but the fun fall color and exciting winter twigs makes it a four season plant.

Fall Color

Yellow Fall Color on this Dogwood looks especially bright with the evergreen background.

Many Dogwoods also sport great fall color. The fall color is primarily in sunset shades, reds and yellows, and looks especially fantastic with an evergreen backdrop. On some varieties the color of the leaves turning is only enhanced by the unique twig colors – clear yellow leaves with bright red stems. Beautiful!

Photo courtesy of Pat Breen Oregon State University

Winter Twigs

Some types of dogwoods are known primarily for their winter twig color – most often called Red Twig Dogwoods or Yellow Twig Dogwoods. ‘Midwinter Fire’ is a popular cultivar, but there are a wide variety to choose from.