October 2014 – The Garden Professors™

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.

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

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.

Scenes From A Zoo

The other day I went to a local zoo with my family. I’m not a big zoo lover. I hate to see animals in cages and kept from their natural wanderings and habits, but this zoo serves as a rescue, so I didn’t complain too much. As we were walking around I couldn’t help but notice the following container which I can only suppose once served as a food or water bin for one group of animals or another.

I really liked that quote. I wish I knew where it came from. Then, just a few minutes later, I saw this.

Hmmmm….now don’t get me wrong, I’d much rather see trees bound up and tortured than animals. But really, the natural world includes many different living organisms that interact with each other, and with us. Each is deserving of our care and respect. The way this poor tree is planted shows a complete disrespect for its life. Too deep — and it looks like more soil will be applied to fill the bed! This is just sad. Look, if we’re going to have zoos then let’s try to make them into places that celebrate the natural world.

The great urban potato experiment

I don’t grow vegetables at home, mostly because I don’t have the space and partially because I don’t have the time. But I did want to try the potatoes-in-a-barrel method, which I also tried last year. But this year I planted about 6 weeks earlier (end of April) than I did the previous year (mid-June). Here’s my mid-October harvests from both years:

Next year I’ll try planting even earlier. It’s not a huge harvest, but it’s fun to do, especially with kids. A richer media (like a green compost along with soil) might give you a better harvest.

If you want to try this yourself, here’s how to do it:

1) Use a plastic trash bin with holes drilled into the sides. Be sure to locate the barrel in full sun.

2) Put a layer of soil on the bottom, and add potatoes. (You can cut them into smaller portions, each with an eye, if you don’t have as many sprouted ones as I did.)

3) Cover with soil and water well.

4) As shoots and leaves emerge, continue to add soil or other media to the barrel, leaving the tops of the shoots and a few leaves exposed. I used a mixture of soil and composted wood chips. Water well.

5) Continue to add media as needed, and continue to water through the season.

6) When leaves begin to die back, you can dump the barrel onto a tarp and pick out your potatoes. Save the media for next year’s barrel.

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.

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.

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.

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.

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.

Cool plant of the day: Canary Bellflower

I’m such a plant nerd that a few years ago I actually decided to get Canarina canariensis, the Canary Bellflower, for no other reason than that it is one of the very few members of the campanula family that has red-orange flowers instead of the usual purple-blue ones.

A Platycodon showing much more typical coloration for this family

Okay. Maybe that isn’t the most normal reason to add a plant to one’s garden, but I am VERY happy I did.

That color!

I’ll admit, it isn’t a plant that is particularly well adapted to life here in Michigan… as the latin name suggests (twice!) it is native to the Canary Islands off the West coast of Africa, where the climate is consistently dry, fairly cool, but never freezes. The summers are extremely dry, with a short rainy season in the winter. And the Canary bellflower has adapted to that by dying back to the thick fleshy roots in the summer, and then sending up the long trailing stems and flowers in the winter when the rains come.

That isn’t ideal for growing here in Michigan, but I’ve found I can get it to grow here pretty easily, actually. It is growing and blooming like crazy right now, and once it gets cold, I’ll move it inside, and let it dry out. As the soil dries, the plant goes dormant, so it can sit there patiently until spring and more settled weather when I can water and set it off into growth again. It works, and though it is a bit more work than most of the other plants I grow, it is worth it. I like looking at the lovely flowers, and speculating about the unique evolutionary path that caused this one genus to develop orange flowers while the rest of the family largely stuck with the tried-and-true purple.

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.

Source: 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.

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.”

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.