New Hort Research that Gardeners Can Use, September '09 Edition

By Jeff Gillman, associate professor of horticulture at the University of Minnesota.  Jeff's earlier quarterly updates are archived here. 

First, a Worry
I worry about transgenic plants. To be a little more specific, I’m not one of those people who believe that no genetically modified plant should ever see the light of day, but I do worry that some of the things which we’re releasing into our environment could harm us, or the species around us, if we’re not really, really careful.

One of the transgenic crops with the most potential to cause problems, at least in my mind, is transgenic turfgrass which has been modified to resist herbicide.  I worry because I see the potential for grasses such as this to invade the ground where we grow our crops and become superweeds. 

Recently I noticed an article by a group of researchers who made tall fescue resistant to a particular group of herbicides.  Don’t get me wrong; I don’t think that this is the end of the world or anything, but I hope that these researchers know what they’re doing and that if this crop is ever released (and it might not be – many studies are done just to prove that they can be done), plenty of care is taken to make sure we’re not putting ourselves into a bad position if it escapes cultivation.

That said, on to more important (at least in the short term) things - a few of the great articles published over the last few months.

Houseplants that Clean Air
So, you know those crazy air cleaners that you can buy at Hammacher Schlemmer?  Well, it turns out that your house plants can clean the air, as well.  Twenty-eight house plants were tested for their ability to remove five organic air pollutants, including such things as toluene and terpene.  Of the plants tested, the best were English ivy, red flame ivy, wandering Jew, Sprenger's asparagus fern and wax-plant, but the authors were careful to point out that different plants are better at removing different things, so it’s best to have a variety of houseplants living on your tables and windows.¹

Getting Orchids to Bloom
Having trouble getting your Phalaenopsis or Doritaenopsis orchids to bloom?  The problem may be that you’re keeping them too warm.  For both of these orchids it’s best to keep temperatures below 79 degrees F. during the day to promote blooming.  If temperatures do climb over 79 degrees and stay there for more than 8 hours it could prevent your orchid from flowering, at least until temperatures drop again.²

Wilt-Free Geraniums
Researchers in Florida took a look at 61 different geraniums to find out which were most resistant to bacterial wilt.  In general, they found that zonal and ivy geraniums don’t have much resistance. Regal geraniums don’t have much resistance either, though the cultivar ‘Elegance Camelot’ shows some promise.  But there are a few scented geraniums with resistance, including ‘Snowflake’, ‘Old Fashioned Rose’, ‘Apricot’, ‘Peppermint rose,’ and others.  Even though these geraniums may have resistance, if there is a cut on the plant, the disease may be able to overcome the resistance.³

Mulch Options
Thinking of planting a tree in an urban lot and using mulch to protect it?  Be careful what you use.  When redbuds and baldcypress were grown in Texas there were distinct advantages to using organic mulches such as pine-bark mulch.  However, crushed bricks used as mulch seemed to have a negative effect on the trees.  Surprisingly, the researchers found that performing better than either bare soil or bricks as mulch are certain plants - like St. Augustinegrass - grown around trees.⁴

Breaking - Trees Need Water!
And our “Who woulda thought?” award this quarter goes to a study which shows that not watering trees when they’re first planted isn’t good for them.  Of course there is more to the study than that.  The authors also determined that, of the lindens, little leaf linden and silver linden were most resistant to drought and that, of the Norway maple cultivars tested, ‘Emerald Queen’ and ‘Deborah’ were the most resistant.⁵

Wandering Jew photo by Crows to Burnaby. Study details below the jump.

1.  Yang, D. S., S. V. Punnisi, K. C. Son, and S. J. Kays. 2009.  Screening indoor plants for volatile organic pollutant removal efficiency. HortScience 44(5): 1377-1381.

2.  Newton, L. A., and E. S. Runkle.  2009.  High-temperature inhibition of flowering of Phalaenopsis and Doritaenopsis orchids.  HortScience 44(5): 1271-1276.

3.  Norman, D. J., Q. Huang, J. M. F. Yuen, A. Mangravita-Novo, and D. Byrne.  2009.  Susceptibility of geranium cultivars to Ralstonia solanacearum.  HortScience 44(5): 1504-1508.

4.  Arnold, M. A., G. V. McDonald.  2009.  Groundcovers and inorganic mulches, and masonry surfaces differentially affect establishment and root zone characteristics of urban trees.  Arboriculture and Urban Forestry 35(5):232-240.

5.  Fini, A, F. Ferrini, P. Frangi, G. Amoroso, and R. Piatti.  2009.  Withholding irrigation during the establishment phase affected growth and physiology of Norway maple (Acer platanoides) and linden (Tilia spp.).  Arboriculture and Urban Forestry 35(5): 241-251.

Comments

[Layanee]

Always a wealth of information, Jeff. Thank you. I am waiting for your new book 'The Truth about Turfgrass and the Four Step Fertilization Program'! I know, it would be short but people need to be told what to do and why.

[Micah]

Now I can justify the jungle at my work desk as beneficial to the office atmosphere.

I just wish plants could clean out the communal fridge and microwave, too. ;)

[Kathy J, Washington Gardener Magazine]

Just watch what those houseplants are potted in and where you got them. Plastic off-gases. Some growers soak the soil in pesticides and you'd never know it. I did a short blog post on a recent study done on it here washingtongardener.blogspot.com.

[Ginny Stibolt]

Thanks Jeff. Great information.

But what about peace lilies? Here's my "piece" on them: http://sky-bolt.com/peacelilies.htm . I include a link to the NASA study on house plants.

[Katie]

*blushing and gushing* I love your books, Jeff!

I have to say, that I stumbled upon the whole orchid blooming thing quite by accident about ten years ago. I set my orchids outside (Phals) and pretty much ignored them until it was PRACTICALLY frosting outside, and then brought them in. Within a few weeks, they pushed up at least one flower stalk, each. Good one!

[Vegetable Garden Blog]

Trees need water? NO!!!

Most of my trees have St. Augastine grass around them and I just did it because it was easier than replacing mulch constantly, who know it was better than mulch!

[LauraBee]

When my employer moved into a brand new office building years ago, the chemical fumes were so strong I'd go home each day with a headache & a sore throat. Then one day I brought in a car load of houseplants - peace lily, pothos, spider plant & such - and surrounded my immediate workspace with them. No more headaches or sore throats & it was much easier to focus with such pleasant company !