Month: January 2010

Baptisia: Beyond the Blue

The Perennial Plant Association recently released the identity of the PPA Plant of the Year – for 2010 it is Baptisia australis (False Blue Indigo).  Various blogs have noted this (including Garden Professor fave Garden Rant) and I’ve read some interesting comments, both pro and con.

True story: I asked for Baptisia at a small rural garden center years ago; the owner said “Don’t have any; but I think I have a Methodist running around here somewheres…”  Badda-bump.

Me? I think it is a truly wonderful native perennial. I’ve had great success with it in both Zone 7b and 6a and teach it as a “bread and butter” component plant for the mixed border. As a PPA member, it certainly got my vote on the last ballot (beats the hell out of last year’s Hakonechloa macra ‘Aureola’ – hard to say and even harder to grow in the Southeast).

The great thing about the PPA “Plant of the Year” program is not just in the promotion of that particular species, but that it opens the door for other cultivars and hybrids.  Two of my favorites:  Baptisia x ‘Twilite Prairieblues’ [sic] and B. x ‘Solar Flare’. Both were bred and/or selected by that delightful genius Dr.Jim Ault, of the Chicago Botanic Garden, and introduced through the Chicagoland Grows program.  Pictured are plants that are have only one full year of growth after purchase and planting (nice full gallons to start with; from Saunders Brothers nursery, located in the greater metropolitan area of Piney River, Virginia).


Baptisia x ‘Twilite Prairieblues’ is a cross between B. australis (our PPA winner) and B. sphaerocarpa – a shrubby, tough little guy with yellow flowers. This fortuitous romance yielded quite a jaw-dropping color combination of dusky violet with a yellow keel petal. These puppies are in our campus horticulture garden.

Now take a gander at B. ‘Solar Flare’ – a “complex hybrid, probably open-pollinated” of B. alba (white-flowered), B. tinctoria (yellow-flowered), and B. australis. This is what can happen when a whole bunch of species and hybrids are planted close together (cocktails and/or bees are usually involved). From my own garden:

Buttercup-yellow fades to warm apricot, then to plum – the thing absolutely glows in the late afternoon sunshine.  Gosh, I miss summer…

Sigh.

Is Petting Your African Violet a Good Idea?

As some of you know, I post a research update every three months or so on  Susan Harris’ blog www.sustainable-gardening.com as well as on GardenRant.  This update reviews scientific articles which might be useful to gardeners.  Anyway, I just finished up a new edition earlier this week — which will probably be posted soon — that included one of the more interesting articles  that I’ve seen recently.  For my post today I thought I’d spend just a couple of paragraphs telling you about it.  Unfortunately it’s not one that is readily available online, so I’ll give you the reference at the end of this article, but few of you will be able to see it without going to some effort.

So, what is this article about that has me so excited?  Well, OK, excited might not be the word — amused might be a better word.  So what is this article about that has me so amused?  It’s about rubbing African violets with gloved hands or non-gloved hands treated with body lotion (Simply Basic Melon Delight Body Lotion).  A researcher went to the trouble of rubbing these plants with their hands for 30 or 90 seconds at a time, 3 times a week, and then measuring plant response.  And the results?  Plants without any rubbing did best, followed by rubbing with a gloved hand, followed by rubbing with hand-lotion treated hands.  And yes, 90 seconds of rubbing was worse than 30 seconds.

So, what does this research mean to you?  Actually it probably has important implications for the African Violet industry and those who work in it, but to me it just reinforces the idea that plants are not pets…..

The Article:  Brotton, J. C., and J. C. Cole. 2009. Brushing using a hand coated with body lotion or in a latex glove decreases African violet plant quality and size.  HortTechnology 19:613-616.

Better Red than Dead!!!

David, one of our newer readers, asked why his red-stemmed roses seem to be more cold hardy than the green-stemmed cultivars.  So today’s blog will be dedicated to a brief discussion of why it’s better to be red than dead.

The brilliant red, blue, and purple colors seen in flowers and fruits are due to anthocyanins (and the closely related betacyanins).  These water-soluble, non-photosynthetic pigments are also commonly found in stems, leaves and other vegetative tissues.  In 1999 I wrote a review article exploring the reasons that leaves and stems might turn red.  A few years later I wrote another review, more specifically looking at how anthocyanins might influence plant water relations.  (This last phrase is plant physiology-geek jargon, and I have to admit that the class I took on this topic during my PhD work was the hardest, and probably most hated, of all the classes I took.  And now it’s turned out to be one of the most valuable.  Go  figure.)

While you hard-core types can read the review articles that I’ve hot-linked above, what I’ll try to do is summarize my hypothesis for why leaves (and stems) turn red.  Some leaves are red when young, then turn green when older.  Green, deciduous leaves turn red before they fall off in the autumn.  And some plants are genetically programmed to have red leaves all their lives.

The environment can also influence leaf reddening.  Drought, nutrient deficiency or toxicity, salts, heavy metals in soils, cold temperatures, low soil oxygen, whew!  All of these environmental factors have been attributed to temporary reddening.  What do these factors have in common?

It turns out that all of these environmental stresses directly or indirectly affect the ability of plants to take up and/or retain water. Because anthocyanins are water-soluble, they effectively dilute the concentration of water in the plant.  Look at it this way: any limited area will only hold so many water molecules.  A test tube of pure water has the maximum number of water molecules possible.  A test tube of water plus sugar (or salt, or anthocyanins for that matter) will have fewer water molecules, because the other substances take up space, too.  So effectively, anthocyanins reduced the apparent concentration of water in plant tissues.

Why is this important?  Well, anthocyanins in leaves helps reduce water loss, because the concentration of water in the leaves is reduced and evaporation slows down.  They also could serve as antifreeze compounds, allowing red leaves (and stems, David!) to be more cold hardy.  And if anthocyanins aren’t amazing enough already, they also (1) bind and transport sugars during fall leaf color change, (2) protect tissues against high levels of solar radiation, and (3) are natural antioxidants.  (That’s why you’re supposed to eat red fruits!)

I could go on and on, but I hope this might help explain why David’s red stemmed roses might be more cold hardy than the green variety. (And my thanks to my daughter Charlotte for allowing me to use her photos here.)

Post-holiday Poinsettia Fatigue

You’ve seen them. The saddest thing ever – a poinsettia, still in its little foil sleeve, tucked into the corner of the doctor’s office/bank/etc. In June. 
Photo courtesy of Beth Bonini http://beedrunken.blogspot.com
So iconic, there’s even a rock band in St. Paul called “Dead Poinsettia.”

Every year about this time, I get asked “how do I care for my poinsettia so it will bloom next year?” by friends, students, random callers, and random newspaper writers. 

Two words: Chuck it.

Four reasons:
1) Unless you have a greenhouse, you probably can’t replicate the growing conditions that resulted in that lovely, leafy, perfect plant. That poinsettia has been grown under optimal temperature, humidity, fertilizer, and high light conditions.  It’s also been sprayed with plant growth regulators – often multiple times, to keep the internodes from elongating.  Even with all the breeding for a compact habit, they still want to streeeeetch to be the shrubs/small trees their forefathers were back in Mexico.

2) Day length. Poinsettias are obligate short-day plants, which means they require a long dark period (yes, I know, why don’t they call them obligate long night plants) to become reproductive, resulting in red (or pink or cream) bracts and the little yellow flower-thingy in the center (the cyathia).  You can, of course, stick it in a dark room at 5:00 p.m. and remove it to a lighted area at 8:00 a.m., every day for the months of October and November.  Until you forget over that long weekend and leave it in the dark for three days…

3) Help stimulate the local “grower” economy.  Consumerist, I know, but wholesale and retail greenhouses grow poinsettias to keep their full–time employees working during what is otherwise a very dead time in the ol’ floriculture business.  Seldom do these businesses make much of a profit on poinsettia; the plan is to keep everyone busy and generate a little cash flow.  Now, some growers/garden centers go above and beyond the usual 6” red point, with unusual cultivars in a range of colors and sizes, hanging baskets, poinsettia “trees”, etc.  This has proven to be a great strategy for some enterprising growers.

4) Poinsettia = total whitefly magnet.

In light of the above, I recommend enjoying your poinsettia until the leaves start dropping…then once it reaches the “less than fresh” stage, add it to the compost pile. Next season, go to your local independent greenhouse or garden center and buy a new one.  Finally, if you are one of the hard-core, stick-with-it types that has been successfully reblooming the same poinsettia for three years running, congratulations! You have much, much more patience than I do.

Disclaimer:  My Master’s research was on poinsettia and the effects of nitrate- N:ammonium- N ratio on growth thereof.  Five treatments x 6 replications x 3 cultivars = 90 poinsettias, off of which I picked every leaf and bract to run through a leaf area meter. The latex oozing from the petioles made for a gloppy mess and the whole process took five days.  Even 15 years later, I can barely look at a poinsettia without cringing. Pleh.

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If I’ve seemed distracted for the last few months, this is why

I just got this today – it releases in February!
Isn’t it a great cover?

And this one came out the week before Christmas – my holiday gift to myself!  (You try riding herd on 21 different authors and see if you like it!)

Getting these books done was a major milestone, and I hope that this year I might have time for some new projects.

Happy New Year!

Do landscape trees need nitrogen fertilization?

I’m in Grand Rapids this week attending the Michigan Nursery and Landscape Association/Michigan Turf Foundation Great Lakes Trade EXPO.  The topic for my talk today was Landscape Tree Fertilization.  That might not sound like a subject that would generate controversy, but as with most things, there are camps emerging.  There is a rising chorus of folks that suggest that landscape trees should not be fertilized with nitrogen.  There are a couple of lines of evidence that bolster this point of view.  First, many systematic studies on the growth response of street trees or landscape trees often do not show a response.  There are numerous examples of this, for example, in Arboriculture and Urban Forestry (formerly J. of Arboriculture).  The second line of evidence for not fertilizing landscape trees relates to the relationship between tree nutrition and susceptibility to insect pests.  This argument relies on the ‘growth vs. defense’ hypothesis and suggests that fertilization promotes growth at the expense of defense compounds; essentially making fertilized trees tastier to insect pests.

So, in light of this, why do I suggest that landscape trees should receive 1-2 lbs of N per 1000 sq ft. every 2-3 years?  First, we need to understand that nitrogen is constantly lost from landscape systems.  In forests, trees take up nutrients from the soil, translocate them to leaves, shed the leaves, and the nutrients are ultimately returned to the soil in a cyclic process.  In landscapes, leaves are usually raked or blown and removed from the cycle.  Soil nitrogen is also lost due to nitrate leaching.  Additionally there are often key weaknesses in some of the papers that purport to show no response to fertilization.  For example, Ferinni and Baietto (Arb & UF 32:93-99) found no response of sweetgum trees to two levels of fertilization.  However, the data show that the control trees, which were not fertilized, had similar (and fairly high) foliar N levels as the fertilized trees.  This pattern can be found in several similar studies.  The more appropriate conclusion for these papers should be “Trees that are not nutrient deficient do not respond to fertilization”.  Similar issues pervade studies related to the growth vs. defense hypothesis.  Why would one presume that a nutrient deficient plant would be better able defend itself against insects attack than a tree that has adequate nutrition?  Ideally, fertilization decisions should be based on visual symptoms and soil and foliar samples.  Nevertheless, low rates of N from either organic or inorganic sources will make up for losses from the N cycle and maintain tree vigor.

It should be noted that the rates I’m suggesting are considerable lower than those that are found in some older extension literature, which recommend rates of N up to 6 lbs for 1000 sq ft.  As a point of comparison, Midwestern farmers apply 150-200 lbs/acre to grow a crop a corn.  The 6 lb rate for landscape trees works out to around 260 lbs per acre!

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