July 2010 – The Garden Professors™

Friday quiz: The case of the bumpy maples

OK, this Friday’s quiz is the real deal: everyone gets to play “Extension Specialist for a Day”. I am stumped on this and so are my colleagues here at MSU. I used to work for a guy who liked to say, “None of us is as smart as all of us”. Let’s put it to the test.

The photos below come from a nursery here in Michigan. The trees are container-grown Red sunset maples. Pretty routine crop around here. The trees look fine: good color, full crowns, growing well. The only problem is that nearly all of the trees have bumps along the bottom 8” or so of the trunks. The grower is concerned, and rightly so, about consumer acceptance of the trees. The trees have been examined by a highly qualified pathologist – no evidence of fungal disease; and by a highly qualified entomologist – no evidence of insect activity. The grower is sitting on several hundred of these trees. What should I tell him?

NOTE: The name of the nursery is confidential – they just used the calipers from Schumacher’s in the photo.

Where to draw the line on a vine

Last week’s column on “why do nurseries sell this plant?” struck a chord with many readers as well as with Holly! So here is this week’s submission: that ubiquitous vine, English ivy.

First of all, we’ll stipulate than many ivies are sold as English ivy (Hedera helix) but may be entirely different species. Genetic research on invasive ivy populations in the Pacific Northwest identify most as H. hibernica (aka Atlantic ivy), with H. helix making up only 15% of the invading populations. Regardless of their species identity, it’s obvious that Hedera is a genus with the potential to escape gardens and invade remnant forests or other environmentally sensitive areas. It grows so vigorously that it can create monocultural mats on forest floors; it grows into trees where its sheer weight can break limbs and in some cases topple entire trees.

But what about other regions of the country – or the world, for that matter? In colder climates, Hedera spp. are much better behaved, dying back to the ground every winter and rarely able to flower and reproduce. The absence of a seed bank means the vine can be kept in check more easily. And it does tolerate tough environmental conditions where other groundcovers might not succeed.

Yet consider another invasive: kudzu (Pueraria montana var. lobata) For decades this noxious weed was thought to be too cold sensitive to expand past the American Southeast. Yet populations have been found in Maine, Oregon, and most recently in Ontario, Canada. Plants adapt!

So – is it worth the risk to buy a plant known to be invasive elsewhere, simply because it’s not a problem yet?

And why oh why do nurseries in Washington state continue to sell Hedera spp. as ornamentals?

The Importance of Not Leaving Your Veg Garden Unattended for a Week in July

Small dog snout + normal-sized cucumber provided for scale.

This problem is self-explanatory and probably not at all atypical for our readers. Pattypans became UFOs; grey zucchini, footballs. Note that it’s been very dry here in the Blue Ridge. I shudder to think what would have happened with normal rainfall.

Beans amuck! Scared the hell out of Joel when he opened the fridge. But they wouldn’t fit in the bucket!

If you haven’t tried yard-long beans, give them a shot sometime. Super easy to grow, just need the usual pole-bean structure. Pick daily, or they get out of hand. They have a rich, “beany” flavor and no strings attached. Best sauteed – I toss them with a bit of sesame oil and soy sauce in honor of their Asian heritage. Leave ’em long to impress the kids! I bet one or two beans equals a full serving of vegetables.

Yard-longs (Vigna unguiculata subsp. sesquipedalis) come in both green and a dark red that keeps its color after cooking! They’re actually in the cowpea genus. Normal green bean at top of plate for scale (it now has a complex).

The importance of knowing your plants

One of the first courses a horticulture student takes is plant materials, or, in the case of a forestry student, dendrology. Why? Pretty simple; it’s hard to select plants if you don’t know what they are and what they’ll do in the landscape. Of course, the classic example is a large tree or shrub planted in a tight spot that eventually devours an entire house. But we usually don’t have to look too far to find situations where a homeowner or landscaper clearly had no idea what plant he or she was dealing with. To wit, a couple of recent examples of poor plant choices (maybe this can be our next series after “Why do nurseries still grow THAT?”)

I spotted the first example wandering through downtown in my hometown of Olympia, WA. At first glace it looks like an ordinary hedge; boxy to by sure, but nothing remarkable.

As I passed by though I noticed the hedge was actually a weeping Norway spruce (Picea abies ‘pendula’ – actually it could have been an ‘inversa’ – the repeated butchering made it hard to tell). Either way, what could have otherwise been a fairly interesting plant had been reduced to a squared-off blob of blech. The other side, of course, is that if a squared off blob of blech is truly desired there are cheaper and easier ways to achieve the effect.

The other example of the perils of not knowing your plant material comes from northern Michigan. This case represents that other extreme of trees that grow too large for their space. Here the homeowner wanted to screen his house (on the left but out of camera range to protect the guilty!) from the railroad track on the right of the photo. Solution: Plant some conifers! Sounds like a good idea to me.

Only problem – the owner chose to plant the screen with dwarf Alberta spruces! As with the blob of blech, the property owner could have achieved the desired screen in a couple of years and at a small fraction of the cost with seedlings from their local conservation district or seedling nursery. In any event, we’ll check back in about 40 years and see how it’s working out for them…

Clematis calamity solved

Some good and creative guesses about why the Clematis leaves had interveinal necrosis. While iron and manganese deficiencies both cause interveinal chlorosis (veins are green, areas between are yellow), the necrosis indicates tissue death between the still-living and green veins. Very simply, this has been caused by water loss.

During transplanting of the vine, I had to remove them from the fence and lay them out on the ground. They remained this way for a couple of days. For much of the foliage, this meant that the lower leaf surfaces were now exposed to the sun. As with many broadleaved plants, the upper and lower leaf surfaces are morphologically distinct: the upper surfaces have a thicker waxy cuticle and epidermis, with few stomata, while the lower surface lacks much of the cuticle and is loaded with stomata. When the leaves are turned upside down, the shade-adapted lower surfaces now receive intense sun exposure: water evaporates quickly from these unprotected leaves and the tissue dies. The only parts of the leaf that don’t die are the veins, which remain full of water as long as the roots are functional.

So both LisaB and Benjamin identified sun exposure as the culprit behind the damage. But as with many environmentally-induced plant problems, the ultimate cause is water stress.

Friday quiz – yet more clematis calamity!

If you’ve been following the saga of our clematis, you’ll know that first they suffered iron toxicity (from the waterlogged soil they were in) and then were dug up and replanted in containers. Last week I showed you what happens when you vigorously work wet soil – yet more waterlogging! During the transplanting process, I took more pictures:

This damage is NOT from the iron toxicity problem. It appeared during the transplant process. What caused it?

Answer on Monday!

Jicama (The Yam Bean)

Every once in awhile I get the urge to try and find something interesting in old literature, and today was one of those days. So I went over to my pile of old “Journal of Economic Entomology” journals and snatched a 1943 issue from the top. The pest issues that we had to deal with during the war years were interesting because resources were tight — we had DDT (and lead arsenate), but all of it was going to the front to protect our soldiers from lice. So scientists back home were trying new things. One which I had never heard of before today was getting a serious look: The yam bean. The yam bean is a tropical legume which has a great deal of potential as a high nutrient food crop (the root of the bean is what is edible, not the seeds). The food part is interesting to me, but more interesting is the fact that a dust could be made from grinding the beans into a powder which would kill insects. After looking through some articles I discovered that the primary source of toxicity in the yam bean is rotenone and some similar chemicals. I’m not a big fan of rotenone, still, this plant is fascinating. An edible root and seeds which can be used very effectively as an insecticide. Why wasn’t this plant more common 50 or 100 years ago? What other plants are we missing out there which are useful?

Why do nurseries sell this plant?

I wish I were more like Holly…wandering around nurseries finding pretty and unusual annuals and perennials to get excited about. Instead, I seem to gravitate to plants that annoy me.

Today while looking for some trellises (for those containerized Clematis vines that I’ve been torturing) I saw pots of the Equisetum hyemale (“a tall, evergreen, spreading, reed-like grass”) for sale:

As readers of this blog surely know, Equisetum spp. – or horsetails – are not grasses but primitive relatives of ferns. That taxonomic blunder aside, the thought of deliberately planting any Equisetum species in a landscape sends shivers down my spine.

Now E. hyemale is not as weedy as E. arvense, but in nearly every seminar I give on controlling weeds with mulch someone asks about getting rid of horsetails. Short answer – you pull. And pull and pull. There’s no good herbicide for them, nothing seems to eat them, and they spread aggressively.

And speaking of eating, did you know that horsetails are poisonous? They contain an enzyme (thiaminase) that deactivates thiamin (vitamin B1) in the unfortunate consumer’s body. The most common victims of horsetail poisoning, ironically, are horses. Horsetails are considered noxious weeds in pastures used for grazing – and yes, they are native to the United States.

Sure, horsetails are interesting looking plants. But do you really want something in your garden that the production nursery describes as having “indefinite spread?” And how does keeping them in a pot, as one production nursery recommends, keep them from spreading spores? Especially if you plant them “in or around ponds and streams?”

I just think this is such a bad idea for home landscapes. Even if it is a native species.

Lamb’s Ears Revisited

A bit more on my recent travels to the big floriculture conference in Columbus, Ohio. I always try to make it out to the Chadwick Arboretum & Learning Gardens, on the campus of THE Ohio State University. There are several components, including trials, a large arboretum, and several small gardens. My favorite is the Steven Still Perennial Garden. It’s a lovely mixed garden, designed by Adrian Bloom (Blooms of Bressingham), and was installed in ONE DAY by their garden volunteers – 2005, I think.

Watching it grow has been fun. I noted [ with pleasure] that they’ve already had to start cutting back and removing some things. This makes me feel better because I am The Queen of Planting Too Close

A few highlights:

I thought of y’all when I saw
this…remember our conversation about Stachys the other day? Here’s a
new one on me: Stachys byzantina ‘Silky Fleece’. What teeny, tiny
little leaves! And seemed to be limiting itself to a small area on the
edge of the border. Introduced in 2006 by German seedmeisters Jelitto
Perennial Seeds. They missed the boat on naming it…could have all kind
of fun with ‘Little Lamb’ or even ‘Mary’s Little Lamb’ as the director
for their North American office is Mary Vaananen. Heh.

My foot is just in there for scale – I’m really not that inept a
photographer.

A gorgeous flock of Rhus typhina ‘Tiger Eyes’. Hardy to Zone 4, the foliage is golden in summer, blazing apricot in fall, a wonderful shrub accent in any garden… What? Hang on a sec.

Correction:
That’s Rhus typhina ‘Bailtiger’ PP16,185. Trade name is First Editions® Tiger Eyes® Cutleaf Staghorn Sumac. Well, that took all the fun out of it.

Moving on…

Belamcanda chinensis – Blackberry or Leopard
Lily. A tough cookie, this midseason bloomer takes drought and even
reseeds a little bit in my home garden. The pods burst open to
reveal a cluster of seeds that look exactly like a blackberry. These
weren’t quite that far along, but in between flowering and seed setting, they
do something else interesting..

The petals twist up into these hilarious
little bundles. I have no idea why or what for. Just kind of neat.

All for now!

Clematis conundrum clarified

Friday’s puzzle was tricky! I will preface the answer by saying I don’t do a lot of container plants except for annuals. When I plant up annuals into soilless potting mix (which is dehydrated), I work in the water thoroughly into this fluffy medium. Friday’s situation was a little different. The Clematis are more or less permanent residents in these planters, so I use real soil rather than potting mix. (This will reduce or eliminate the shrinkage you’ll get if you use soilless media, as these highly organic materials steadily decompose.)

But what I thoughtlessly did was to mix water into my nice screened clay loam like it was a potting mix. The result of vigorous mixing is to break down the soil structure and drive water into all of the pore spaces, resulting in a totally waterlogged soil:

After my "D’oh" moment when I realized my error, I potted the second Clematis into loose soil and let gravity work the water into the larger pore spaces. This passive approach protected the soil structure and left some of the pore spaces filled with air rather than water, so that the water drained through rather than sitting on top of the compacted soil:

This demonstrates one of the rules of working with landscape soils: you should avoid any potential compaction when the soil is wet. (It’s the same reason you shouldn’t stomp on wet backfill as you’re transplanting trees and shrubs.) As Ginny pointed out, you’ll create a cement-like structure – not conducive for water movement, oxygen availability, or root growth.