The Garden Professors™

You think YOU had a bad day…!?!

I'm itchy all over. — I’m itchy all over.

Just downloading some photos from the end of the summer, and found this. Rarely can I work up sympathy for a tomato hornworm (Manduca quinquemaculata). Though the moth is quite lovely, the caterpillars really did a number on my tomatoes (and two spindly eggplants) this year, and I recall joyously taking this photo in August.

However, I’ve had a rough Monday, and can kind of relate to being covered in Braconid wasp pupae. The larvae have chewed their way through the caterpillar, to spin their grisly cocoons of death (would have made a great post a couple of weeks ago) and dangle there in the breeze until emerging. I know it is nature’s way, but, dang.

Get a handle on your microclimates

Practically the first thing a budding gardener (at least in the US) learns is their USDA winter hardiness zone. Based on average winter low temperatures, hardiness zones have many flaws but are still a very useful tool in figuring out what plants can and cannot survive your particular winters.

Right after learning about winter hardiness zones, we generally hear about microclimates – the idea that small precise locations within our garden may be, sometimes significantly, warmer or colder (or wetter or drier) than the surrounding climatic norms. The most pronounced producer of microclimates in most people’s gardens is their house – the sunny southern and western walls in particular can be markedly warmer than the rest of your yard. If you have hills, you also get frost pockets in low lying areas and warm south-facing hill sides.

But just how much warmer ARE your microclimates? I used to live in a drafty, poorly insulated nearly 100 year old house which had VERY warm microclimates all around it because all the heat my furnace put out was rapidly leaking out into the outside world. Great for growing plants that normally wouldn’t take my winters, but oh, the heating bills! A modern, well insulated house leaks a lot less heat out into the garden. Over time in a garden, you can learn by trial and error just how far you can push growing tender plants in warm microclimates by planting things and watching them die or survive. But there is an easier and faster way to figure out your microclimates. Collect some actual data, getting firm numbers of how warm and cold different parts of your yard are.

I’m heading into the first winter in a new garden, and getting ready to deploy a handful of cheap mechanical min-max thermometers. I’m placing one out in the open, the others against the south wall of a shed and other places I think should prove to be warm microclimates. Out they go, and after particularly cold weather – or just in the spring – I can check the different minimum temperatures they’ve recorded. A few degrees differences isn’t worth worrying about, but get to 10 degree differences, and you are talking a whole winter hardiness zone warmer.

In addition to comparing different locations in my garden, I also like to compare the actual temperatures I’m recording with those from local official weather stations (to do that, just go to www.weather.gov, enter your zip code, and then click “3 day history” on the right side of the screen). The zone map is created based on readings from weather stations like these, and if your particular yard is consistently showing temps warmer or colder than the local official readings (provided, of course, your thermometers are accurate), you should adjust your winter hardiness zone accordingly.

Finally, a min-max thermometer is a great way to test various winter protection methods. Tender plants can be insulated with a thick layer of leaves or (my favorite) cut conifer branches or even styrofoam boxes. How well do these protections work in your garden? Tuck a thermometer in with the plant before you cover it and then, come spring, check the minimum temperature it recorded against what you saw in the open air. Again, a difference of 10 degrees Fahrenheit corresponds to a whole winter hardiness zone warmer, giving you real actionable information about what you might be able to over-winter with the help of different sorts of insulation.

It is worth reiterating that minimum winter temperature is only one of a myriad of factors that go into winter hardiness, moisture, duration of cold, health of plants, and even summer heat matter as well, but winter lows are important, and it can be easily and precisely measured. So why not get some numbers on it so you can have a better idea of just what tender plants you can get away with in your various microclimates? A few thermometers is a lot cheaper than putting out a bunch of rare perennials and having them freeze out on you.

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!)

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.

Digging these wasps!

After writing about the unusually bad scourge of Japanese Beetles earlier in the month, I thought I’d continue on down the “garden bugs” path. The Japanese Beetles have died down, but now we have oodles of these pretty black and yellow-spotted waspy things around. They’re everywhere, and in large numbers. I planted some buckwheat over our potato garden bed, and it is covered up with them. The point of the buckwheat was as a primo late-season nectar source for our honeybee hives as they prepare for winter. Blooming for the last week or two, I kept checking it expecting to see happy bees, feasting away. Nada. Just the wasps.

Intriguing. A brief googling revealed the wasp to be Scolia dubia, one of the “digger wasps.” They rarely sting, and better yet -their larvae are parasites of Japanese Beetles! All that swooping around over our so-called lawn is apparently the mating dance, then the female digs into the soil to find the grubs. After stinging the grub, she lays an egg…and you see where this is going. Cozy winter grub cocoon for the pupating larvae!

Back to the bed of gourmet buckwheat. I’m thrilled to see all those wasps feeding on the nectar. Eat, dig, and be merry, ladies! But what about the honeybees – seemingly ignoring this glorious patch of buckwheat planted just for them? I don’t need any more picky eaters…aren’t our two dinner-snubbing dogs enough? So I asked Dr. Richard Fell, legendary Apiculture faculty here at Virginia Tech, about this mystery. “Honeybees only work buckwheat in the morning” sayeth Rick. Went out this morning and observed that buckwheat is indeed the breakfast of champions. The entire patch was literally humming with multiple species, including loads of honeybees. I’d only been checking in the evening.

Addendum:
So my post apparently isn’t breaking news. Just came across this as I checked my Scolia spelling. Sounds like they had beetles galore in Maryland as well this summer.
If you’re not familiar with Dr. Michael Raupp, Entomologist and Extension Specialist at University of Maryland, he’s awesome, and his “Bug of the Week” blog is a must. His September 1 post reviews the digger wasp/japanese beetle relationship as well, with more factoids and a lovely video featuring writhing grubs. http://bugoftheweek.com/blog/2014/9/1/white-grubs-beware-the-blue-winged-digger-wasp-iscolia-dubiai-has-arrived