You CAN grow it, but is it worth it?

As winter sets in here in Michigan, I’m seeing gardeners deploying winter protection. Like this, which I saw on a visit to Hidden Lake Gardens with some friends recently:

pinus contorta Chief joseph covered

Well. Isn’t that attractive? Come around to the far side, and you see this:

pinus contorta Chief joseph

Pinus contorta ‘Chief Joseph’ which is a stunningly beautiful conifer, green in the summer, this brilliant shade of gold in the winter. Sadly, those gold needles are also incredibly prone to turning a less brilliant shade of brown if exposed to too much winter sun and wind. Hence the ever-so-attractive sun-and-wind shade they’ve installed here.

Call me old-fashioned, but the point of a garden is to be pretty, and though you CAN wrap delicate shrubs in burlap or upend styrofoam cones over tender roses or even (yes, I’ve seen it) put little roofs over your hardy succulents to keep excess rain off of them, but is it really worth it? For me, if I have to put something ugly on my plants to keep them healthy, it isn’t worth it. In my garden, I’d lean towards something else I also saw on that visit:

Chamaecyparis obtusa Crippsii

Chamaecyparis obtusa ‘Crippsii’ No, it isn’t quite as stunning as the pine… but it will grow and not turn brown, with no fuss.

What about you? Are there plants you are willing to make your garden ugly to keep happy?

 

When trees can’t predict weird weather

Our normally mild corner of the country got hit early and hard with cold weather a few weeks ago. For several days straight, our home thermometer read anywhere from 22-25F. Now, Seattle routinely gets temperatures this low sometime during the winter. But this cold spell came very early – much earlier than our regionally adapted trees and shrubs were used to. The effect on our plants was significant.

20141112_080049Rhodies react to cold but tolerate the freezing temperatures

Trees and shrubs start getting ready for dormancy in the summer. They key in on the progressively shorter days and make biochemical preparations that are unnoticeable. When the first frosty evenings arrive, leaf color changes begin immediately. Chlorophyll, proteins and sugars are scavenged and stored in trunks and roots – we see leaves change from green to red, orange, yellow, and eventually brown. Slowly an abscission layer is laid down at the base of the leaf petiole, and when the layer is complete the leaf dies and falls.

But this year the trees weren’t ready. It got cold really fast, and green leaves died on the trees. And they are still there. Eventually these old leaves will fall, though some of them may stay on until spring.

Cold shocked leavesBoth the hydrangea in the foreground and the styrax in the back have retained their leaves after the cold snap.

What does this mean in terms of tree health? Well, it won’t kill them, but it does set them back in terms of food storage. A lot of the nutrients that were still in the leaves when they froze are lost to the tree. So there may not be as many reserves for winter root growth, or for spring leaf flush. Overall, we could expect to see less than normal growth in established trees and shrubs.

Is it an Elmaple!

So let’s see here…someone planted a nice little Japanese maple outside a hotel, and everyone was happy. Then an elm started to grow next to it, and it looked pretty good. In fact, it looked better than the maple. So, what the heck? Let the elm grow and ignore the maple. And now….At what point do you decide which tree to sacrifice so that the other can live a reasonably healthy life? (Yes, there is a correct answer!)

image

A scary Halloween story

Those of you that have followed the blog for a while know that poor tree planting is one of my pet peeves. It drives me crazy to watch tree installers use backhoes to gouge out gigantic holes and then drop in the intact root ball, clay, burlap, twine and all. But this dig-and-dump method (or “cost effective practice” according to installers) of installing trees often dooms them (the trees, not the installers) to a slow and ugly death. So in honor of Halloween, let me share my latest horror story.

Twice a day I drive down this street in NE Seattle. I’ve long admired the row of dead street trees left to remind us all of our own mortality. A few of these Liriodendron have somehow survived though “survival” seems a generous term. They’re more like zombies, slowly losing body parts but somehow still functioning until someone puts them out of their misery.

Dead #1 Dead #2 Dead #3

One lone tree seemed to defy all odds. Until our latest windstorm, which revealed the cause of all this arboricultural agony.

Downed tree Rootball side Rootball

That’s right, there’s the clay-covered rootball, still intact. Only one root has managed to escape into the native soil. There may be others on the opposite side, but by now (several years after installation) there should have been sufficient root establishment to prevent failure.

Several of us have written about bare-rooting trees before, and while there’s still not consensus on the practice I think we would all agree that the tree planting in this case was not acceptable. There are better ways, and yes they take more time (or “not cost effective” according to installers), but planting trees right mean fewer replacements later.

What’s wrong with my pine tree…? Nothing!

Every once in a while in this line of work we’re actually able to give a homeowner some good news about their trees. A case in point is a call that we frequently get this time of year that starts like this: “My pine tree looks like it’s dying! It’s dropping all of its needles!” If the caller has access to the internet and a digital camera I usually request that the send me a couple of photos; if not, I ask them whether the tree is shedding needles along the outermost part of the limbs or on the interior.

White pine trees often grab homeowners attention as they begin to drop their needles in the fall.
White pine trees often grab homeowners attention as they begin to drop their needles in the fall.

In the vast majority of cases the tree is an eastern white pine (Pinus strobus) and the homeowner is observing is normal needle shed. White pine needles often persist for only two growing seasons. So in the fall they begin to shed their previous-years needles, which often turn an eye-grabbing bright yellow in the process. Actually all pines and evergreen conifers shed their needles; it’s just more noticeable in white pines because they are common in the landscape and their needles are short-lived.

White pine needles often turn bright yellow as they senesce.
White pine needles often turn bright yellow as they senesce.
What's wrong with my pine tree?  As long as the tree is dropping older (interior) needles, it's probably normal needle shed.
What’s wrong with my pine tree? As long as the tree is dropping older (interior) needles, it’s probably normal needle shed.

The lifespan of pine needles varies widely among species. In some species, such as white pine and loblolly pine (Pinus taeda), needles may only persist for two growing seasons. On the other end of the spectrum is bristlecone pine (Pinus longaeva), which can retain needles for up to 40 years. For the most part, needle retention is correlated with shoot growth rate; trees with fast growth rates have fast needle turnover, while slower growing trees have long needle longevity. Of course there are lots of exceptions to this trend and environmental conditions can impact needle life-span as well. For example, needles may shed prematurely during a drought.

Needles on this Austrian pine (Pinus nigra) persist for three growing seasons.  The tree is currently shedding needles formed in 2012.
Needles on this Austrian pine (Pinus nigra) persist for three growing seasons. The tree is currently shedding needles formed in 2012.

Bottom-line: If it’s fall and your pine is starting to drop interior needles, chances are it’s normal needlefall and nothing to worry about.

Pine needles accumulating on the ground.
Pine needles accumulating on the ground.

References
Ewers, F.W. and R. Schmid. 1981. Longevity of Needle Fascicles of Pinus longaeva (Bristlecone Pine) and Other North American Pines. Oecologia 51:107-115
Hennessey,T.C. , P.M. Dougherty, B.M. Cregg, and R.F. Wittwer. 1992. Annual variation in needle-fall of a loblolly pine stand in relation to climate and stand density. Forest Ecology and Management. 51:329-338.
Schoettle, A.W. 1990. The interaction between leaf longevity and shoot growth and foliar biomass per shoot in Pinus contorta at two elevations Tree Physiology 7:209-214.

Walnut warfare

Recently, a question about using black walnut chips for mulch was posted on our Garden Professors Facebook group page. As gardeners know, black walnut has a reputation as a chemical warfare species that will kill anything growing underneath it – a phenomenon called allelopathy. So it’s logical to wonder about the lethality of walnut chip mulches.

To get a good feel for the science behind black walnut’s allelopathic abilities, I was fortunate to find a relatively recent review on the topic (Willis, R.J. 2000. Juglans spp., juglone and allelopathy. Allelopathy Journal 7(1):1-55.). This well-written review includes a fascinating section on the historical background of walnut allelopathy, which was first mentioned in 36 BC by the Roman author Varro. But the science of allelopathy really started less than 100 years ago, when a Virginia researcher noticed the injury caused to tomato plants growing near black walnut (Juglans nigra) in his home garden. Subsequent experiments by him and others suggested that the orangish hydroquinone juglone leaching primarily from leaf litter and hulls.

SONY DSCSource: Wikipedia.

The research results on walnut, juglone, and allelopathy have been nothing if not inconsistent. For every report of toxicity in an exposed species, another report found no effect. In fact, much of the supposed allelopathy might instead be due to walnut’s highly competitive root systems, which could suck up available water and nutrients over a vast expanse of soil.

Black walnut tree Source: Flickr user davidburn

There are a number of other factors that help account for ambiguous results:

1) Juglone is not the only secondary metabolite produced by walnut species. They are loaded with a number of untested phenolics, flavonoids, alkaloids, terpenes and other quinones which could have allelopathic activity.
2) Juglone concentrations vary greatly among walnut species. They also have seasonal variability in the same individual.
3) Light conditions, rainfall, soil chemistry, and many other abiotic factors can influence juglone levels.
4) Organic matter and clay particles in soils can bind juglone, reducing its movement within the soil.
5) Microbial activity breaks down juglone.

Carefully controlled laboratory experiments can demonstrate juglone allelopathy to a number of plant species, especially at the seedling stage. However, there is little evidence from landscape level research to suggest that allelopathy is the reason that plants are damaged by being in proximity to walnut trees. In fact, the author of the review study concludes that even though Juglans species provides the best known and most widely accepted example of allelopathy, there is “still is no unambiguous demonstration of its effect” as “no one has as yet demonstrated that juglone is actually taken up by plant roots.”

walnut tree Source: Wikipedia

Where does this lead us in our discussion of walnut mulch toxicity? Fresh hulls and leaves appear to be the primary source of allelopathy, but not the wood. And even these sources may be quickly neutralized by soil conditions. Therefore, a walnut chip wood mulch should pose no danger at all to landscape plantings.

What’s wrong with this picture?

The  Seattle Times recently had a front page story on what Seattle’s new waterfront might look like. Back in 2009, the city began work on this project, hiring “rock-star landscape architect James Corner, designer of the celebrated High Line in New York City” to develop the big picture. (Note: I’ve been to the High Line and have posted on it before – it’s fantastic.) As you can see from the linked article from the Times, many of Corner’s architectural renditions for the greenway are presented, including this one:

waterfront2
COURTESY OF JAMES CORNER FIELD OPERATIONS AND CITY OF SEATTLE
An architectural rendering shows what a Pioneer Square beach at the foot of Washington Street could look like.

For those of you not familiar with Seattle’s waterfront, it’s built right next to Puget Sound, a huge inland sea connected at its mouth to the Pacific Ocean. So it was with much surprise that I saw what appear to be Douglas firs (Pseudotsuga menziesii) along the cobbled beach. Douglas firs are not particularly salt tolerant, nor would they be very happy with the tidal action or seasonal storms that will flood the beach on a regular basis. Even if these were not Douglas firs (native to Seattle) but some other salt-tolerant species (mangroves?), it’s doubtful they would look as picturesque as the drawing shows. Neither would the rest of the trees in the area, whose root zones would normally extend far into saline soils under the beach and sound.

Am I being picky? No, I don’t think so. Landscape architects should know better than to use plantings as decorations for their designs, like candy sprinkles on cupcakes. Plants aren’t just design elements. Choosing plants that are appropriate to a site is a science as well as an art.

I can’t believe that in the five years that Seattle’s been working on this project that horticultural science hasn’t been a major component of landscape planning.