The roots of the rhody problem

There were several good shots at analyzing Friday’s unhappy rhododendron.  Mature leaf size can be determined by light levels, as both Lisa B and Tom &  Paul suggested.  Moving a plant from a low to high light environment could cause this change in leaf size.  This rhododendron hasn’t been recently transplanted, however, so we can eliminate light levels as a cause.  (And there was no other impediment to light, such as the presence of shading plants.)

Lack of nitrogen was mentioned as well; but a lack of nitrogen would have resulted in chlorosis in newer leaves as well as smaller leaf size.  In this case, the new leaves are not chlorotic.  (The chlorosis on the older leaves is probably a phosphate-induced iron or manganese deficiency.)

Foy alluded to issues with water…and indeed that’s what I believe is happening with this rhododendron.  Plants that exhibit smaller mature leaves in subsequent years are often limited by water.  Full turgor is needed to force leaves to expand fully; without this physical pressure from inside, leaves fail to expand and once cell walls have lignified, leaf expanion ceases. 

Lack of sufficient water during leaf expansion could be related to irrigation, though in our wet spring climate this is rarely a factor.  More likely is a problem with the roots themselves.  Definitive diagnosis would require digging up the plant to find out whether its roots are still encased in clay and burlap (my guess) or if something else is restricting their ability to grow beyond the planting hole. 

Friday puzzle: unhappy rhododendron

Today we have a diagnosis question. Consider this unhappy rhododendron:

While there is more than one problem with this poor thing, the one I’d like you to think about is why the newer leaves are smaller than the old leaves. (They are fully mature.) There are two parts to this question:

1) What is the physiological reason that the leaves are smaller? (In other words, what is directly causing this difference?)
2) Knowing this, what does this tell you about the underlying problem? (This is related to diagnosing what’s happening in the landscape that you could actually see if you knew where to look.)

I hope that’s not too confusing! I’ll monitor the blog over the weekend and add clarification if I need to.

Answer on Monday!

GP Hit List: Ligustrum sinense (Chinese Privet)

[And I don’t mean “greatest hits”, I mean “Mafia hit”]

Gardeners, yardeners, and designers are on a perpetual lookout for a good hedge species. Hedges are useful in so many ways: providing backdrop for a border, making good neighbors, containing football players, etc.  In reference to the latter, the field at Sanford Stadium at the University of Georgia (cue woofing!) is known as “Between the Hedges”.  In the extensive lore of UGA football, everyone makes like it’s some sacred plant, but (gasp!) it’s just plain ol’ privet. Aside to Jeff, my fellow UGA alum: CNN just reported the dubious distinction that Georgia is the #1 party school in the country (again).  Maybe this is why I can’t remember the Krebs Cycle.

Variegated Chinese Privet in all its shrubby glory; photo from University of Arkansas Cooperative Extension.

Back to privet. Designers of D.O.T. landscapes such as medians and interchanges seem especially enamored. Clouds of variegated privet (L. sinense ‘Variegatum’) dot interstates throughout the South.  Yes, it’s tough, useful, variegated, and touted as “wildlife friendly” by some leading gardening resources. The berries are indeed good bird food; therein lies the problem. Seeds pooped out by birds results in the green, non-variegated version – much more vigorous and deposited everywhere. For the record, the variegated form also reverts like crazy.

My family’s farm in northeast Georgia is bordered by the North Fork of the Broad River. Over the years, the river bottom, and then the fence lines at all elevations, have filled with privet. It is, pardon my language, a total bitch to remove and almost impossible to eradicate.  The State Botanical Garden of Georgia in Athens has an entire squad dedicated to eliminating it from acres of river bottom; ironically, only a few miles from Sanford Stadium. Thought of mostly as a Zone 7-9 plant; we have lots of it in the woods here in the mountains – an entire zone cooler.

Distribution of L. sinense; USDA PLANTS Database

Ligustrum sinense is on at least two official Invasive and Noxious Weeds lists by the Southeast Exotic Pest Plant Council and Florida Exotic Pest Plant Council as well as several international lists.  Nursery growers and landscapers across the South know these things. So why, why, why, do they continue to produce and spec it?  “Variegated foliage sells. People see it, like it, and then ask for it. It’s a bread-and-butter item.”  This comment came from the owner of a fairly large nursery that sells to independent garden centers.

Our industry yelps whenever a state or federal mandate threatens to impose restrictions on a best-seller (Hedera helix, for recent example).  There are LOTS of terrific woody plants out there, people.  The Dirr book is now up to 1250 pages – thumb through and pick a few alternatives. Cease and desist with the Chinese privet.



Some of my favorite plants are those that “do something” when little else is.
Do we really need more June-flowering perennials? No!
Well, yes. Never mind.

Edgeworthia chrysantha – “Paperbush” is the common name – is a deciduous suckering shrub , native to China. It usually maxes out around 4′ to 5′ tall and as wide.  The large, matte bluish-green leaves resemble those of Magnolia virginia in shape and are also a bit silvery on the underside.  But that’s not what we’re here for…

An oooh-aaahhh-worthy specimen at the Hahn Horticulture Garden, Blacksburg, VA.

Furry, silvery flower clusters dangle like earrings from the cinnamon stems throughout the winter, getting larger by the month.  

Then by late February or March, they open up, all golden and waxy, emitting a light, sweet fragrance on sun-warmed days.

Blooms at Pine Knot a few Springs ago…

Edgeworthia is ideal for the deciduous woodland environment. Hellebore specialists Dick and Judith Tyler of Pine Knot Farms (Clarksville, Virginia), situate theirs among drifts of spring bulbs and, of course, Hellebores. It’s a soul-stirring sight in March.

I believe the hardiness of Edgeworthia may be underestimated, especially if you go to a little effort to select the right microclimate.  Dr. Dirr lists it as Zone 7 to 8(9). Having enjoyed them at the JC Raulston Arboretum during my doctoral work at NC State (Raleigh, North Carolina; Zone 7b), I found Edgeworthia was little-know here in the Blue Ridge (solid Zone 6, alledgedly 6a).  We ordered some in for our Garden and Hort Club’s 2007 plant sale held in late April – despite my pleading and mark-downs, they didn’t generate much interest from shoppers as they were out of flower. We planted the left-overs in a fairly protected position on the North side of our garden pavilion, and they’re thriving. Snow was heaped up around them throughout January and February and we’ve gotten well into the single digits complete with howling winds a few times.  Despite this rotten winter, they look better than ever, ready to burst into bloom any day now.  Readers, please weigh in: Had any success with it in Zone 6?  And why isn’t this fabulous thing more prevalent in the trade? 

A Brief Discussion on the Wisdom of Barberry as Median Plant

We never know who to blame (or, rarely, thank) for roadside or median plantings. State D.O.T.? Local municipality? Subcontractor to either of the previous?

A few years ago, this appeared in the median of the Highway 460 bypass – the main road leading to Virginia Tech:

I am somehow reminded of Sideshow Bob from The Simpsons…

Two hedge rows. One of  green Japanese barberry (Berberis thunbergii, cultivar unknown); the other of the purple form (Berberis thunbergii var. atropurpurea) Side by side, they make their way up the median, alternating from the right-hand side of the culvert to the left, like two caterpillars in love.  Ooooh, lovely! Or at least SOMEBODY thought so.

Issues: 1) Barberry is a prolific fruit-setter and has made several state’s “Invasives” list.  It’s outright prohibited in Massachussettes (can’t buy, sell, or import it).  In our Blue Ridge Mountains of southwestern Virginia, it is popping up with startling regularity in state forests, road sides, open fields, etc. Interestingly, most of what I’ve seen is the purple form.  2) It’s very thorny. Which means most of the time it is adorned with plastic bags and other perforatable garbage.  3) They are actually mulching, pruning, and weeding this mess, which stretches for at least 2 miles. Best use of state budget/manpower??

I realize purple Japanese barberry is one of the bread-and-butter staples of many nurseries and garden designers. Folks just love the deep reddish-purple foliage.   Virginia Tech’s school colors are maroon and orange, so this is the go-to shrub for campus landscapers and ardent alumni desiring that particular color scheme (see below for our “living VT”). Very fun!  Growing next to a trillium on our section of the Appalachian Trail? Not so much.

Approximately one gazillion people get their photo made next to the VT logo each year – pretty good public relations for a noxious weed.