Archive for small 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.

 

 

 

Small Trees for Fall Color

What trees are small enough to mature in the typical yard space, have low water needs and have full season beauty?

Acer Circinatum "Pacific Fire" photo from Handy Nursery

Acer circinatum ‘Pacific Fire’ photo from Handy Nursery

Our Native Vine Maple is Tried and True

Select a new variety of native vine maple, Acer circinatum, like Pacific Fire with scarlet red winter twigs.  It is attractive in partial shade to dappled sun but the best effects of color, both twig and fall leaf color occur in half day sun.  It can be grown in full sun but this will probably spoil the foliage with leaf scorch.  Plant it in morning sun with dappled afternoon shade for best results.  Matures at 15′ to 20′.

Seven Sons Flower is Great for a Tough Spot

Seven Son Heptocodium photo courtesy of Treephoria

Heptacodium miconioides ‘Seven Sons’ photo courtesy of Treephoria.com

Here’s a tree for a hell strip! Seven Sons Flower, or Heptacodium miconioides, is great for full sun and less than great soil.  You can buy it as a standard, or single trunk tree, which will fit in your parking strip nicely. Or buy the low multi-branched form (pictured) for placement in the landscape.  It flowers in late summer and holds the color of the flower into late fall so you don’t miss out on fall color either even it if isn’t the leaves that glow red; 20′ at maturity.

Use Phoenix Snake Bark Maple for Something New

Acer Conspcium Phoenix photo courtesy of Treephoria

Acer conspicuum ‘Phoenix’ photo courtesy of  Treephoria.com

Here is the newest darling tree Acer conspicuum ‘Phoenix’, or Snake Bark Maple.  It needs regular watering, less after a few years have gone by but is not drought tolerant.  Amazing twig color and the bark’s dramatic color show just gets better and better as the tree matures.  Like all maples, plant up on a mound if you have heavy clay soil.  Good drainage is the key to longevity.

Use Crape Myrtle for Four-Season Interest

Crepe Myrtle - photo taken at J Stone Garden

Crape Myrtle – Focus here is on bark color.  Photo taken at J Stone Garden

My favorite Crape Myrtle, or Lagerstromia, is ‘Tuskegee’, maturing at 15′.  These trees need to be planted in well drained soil or up on a mound.  Don’t plant this tree with an east wind exposure.  Best in full sun or 3/4 day sun.  Winter bark, wow fall color, hot red orange summer flowers, with low summer water needs. Another great variety that is easier to find is Tuscarora, or Lagerstroemia indica x fauriei ‘Tuscarora’.

Crape Myrtle in NE Portland Landscape Design

This Crape Myrtle putting on an early Fall show in a NE Portland front yard.