Tag: winter

Checking up on FreezePruf

As winter continues to hold its icy grip over the middle of the country, our thoughts don’t stray too far from plants and cold.  Recently one of the graduate students in our department, Nick Pershey, brought to my attention a new product called FreezePruf that claims to improve plant cold hardiness by up to 9 degrees F.  Since a couple of degrees of improved cold tolerance can be a big deal (just ask a Florida citrus grower after a 29 deg. F night), nine degrees F. is huge.  At first blush, FreezePruf looks ripe for the Garden Professors’ picking.  The promotional claims are sensational and are followed by the obligatory exclamation points.  “Just spray it on.  It’s like moving your temperature zone 200 miles south!”  So the obvious questions are: What is it? What does it do?  Does it work?

What is it? FreezePruf is a mixture of several fairly common compounds.  These include WiltPruf (a film-forming anti-transpirant), SilWet (a surfactant – helps material spread and stick to leaves), AgSil (potassium silicate), polyethylene glycol (an osmoticum – PEG is widely used in cosmetics and laxatives), and glycerol.

What does it do?  To understand what FreezePruf does it’s helpful to understand how freezing injury occurs in plants and how plants tolerate freezing.  First, remember that water exists in plant tissues between plant cells (extracellular) and within cells (intracellular).  When plants are exposed to freezing temperatures ice forms first between cells (extracellular ice) but not within the cells.   This is due to the fact that water within cells contains solutes that depress the freezing point.  Freeze damage can occur in a couple ways.  One is ice formation within cells (intracellular ice).  Tissues can also be damaged if cells become excessively dehydrated as a result of extracellular ice formation – the ice between cells acts like a salt or osmoticum to continue to draw water of the cell and into the intercellular spaces.  The formulation of FreezePruf apparently acts to depress the freezing point within the cells (due to potassium ions and PEG) and to limit cell dehydration.

Does it work?  At present the only data available on FreezePruf is from the product developers in their patent application.  To date, nothing on the product has been published based on peer-reviewed studies; which always makes the Garden Professors skeptical.  The product development team, however, is lead by Dr. David Francko, a plant biologist and Dean of the Graduate School at the University of Alabama.  Data in the patent application show improved cold hardiness on the order of about 4-5 deg. F for a variety of cold sensitive plants, mostly palms, bananas and annuals.  In some cases the protection was only a couple of degrees but in one case ranged up to 9 deg. F.

What’s the bottom line? For most gardeners the principle benefit of FreezePruf would be to protect plants from the first few early frosts in the fall.  The question is whether you’d rather spray a relatively untested product versus relying on tried and true methods (e.g., bringing container planters in, covering sensitive plants with old bedsheets).  The developers claim FreezePruf can last up to 6 weeks – that could save a lot of dragging bedsheets around the yard.

Caveats: FreezePruf is marketed as ‘Eco-Safe’  – whatever that means – although the MSDS sheets of some of the component products indicate eye and skin irritation are possible.  Until a longer-term database is available I would be cautious of unintended results.   For example, could this stuff make plants more attractive to pets or wildlife?  We’ve seen reduced cold hardiness in conifers using WiltPruf alone, it would be interesting to see some data on Freeze-Pruf on conifers before recommending it for use on those.

Friday Physiology Fun Followup

Astute readers pointed out several morphological adaptations found in drought-tolerant turf weeds:  fleshy taproots, reflective leaf surfaces, etc.  What we can’t see is what many of these plants do physiologically – and that’s photosynthesize using a biochemical pathway that temperate turfgrasses don’t possess. 

This pathway, called C4 photosynthesis, contains some extra preliminary steps not found in plants using traditional (C3) photosynthesis.  The downside:  it takes more solar energy for the plant to photosynthesize.  The upside:  these extra steps allow the plant to "fix" carbon (transforming it from gas to solid) faster, especially when it’s sunny, warm, and droughty.  Practically speaking, this means that C4 plants do not have to keep their stomata open as long and they conserve water more efficiently than C3 plants.

So in the summer – when it’s hot, sunny and dry – the C4 plants in your lawn are operating under optimal conditions, while the C3 grasses go dormant.  The tables turn when the seasons do:  cool, moist conditions favor traditional photosynthesis, and the C4 plants are overtaken by the turfgrasses.

Cool, huh?

Friday physiology fun

It’s still cold and wintery, so let’s imagine ourselves in a happy place…warm, sunny, dry…with dead lawns.

As the photo shows, the turfgrass is dead; this happens every summer during the Pacific Northwest’s droughty summers.  Yet many of the weedy species are obviously thriving.  Why?

Remember, this is a physiology quiz.  You can discount herbicides, fertilizers, etc.  This is a cool (no pun intended) adaptation that many species native to dry, subtropical to temperate environments possess.  And there are serious implications for water use related directly to this adaptation, or lack thereof.

Let’s see lots of brainstorming on this – no points deducted for trying!  (And if you are a true ecophysiology geek, let other people try first before posting the answer.)

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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Let It Snow!

Here in Minnesota one of the things that we need to worry about is the cold.  Over the winter we can see temperatures down into the -30s (even the -40s in the Northern part of the state) and it can damage many of the plants that we grow.  The tops of the trees are usually able to handle these types of temperatures — though a good heavy snowfall can cause a limb to collapse now and again.

The bigger problem is with roots which aren’t able to handle the cold like the top of a plant can.  Once you get 10 degrees or so below freezing you’ve killed the roots of most plants.  Fortunately the ground is a great insulator and doesn’t get nearly as cold as you’d think.  Once you get two or three inches under the surface of the soil temperatures will hover right around freezing for most of the winter.  The plants that are most susceptible to cold are those that are in containers because their roots are above the soil’s surface.  Nursery growers usually protect containers from the cold by consolidating them (pushing them together as in the picture below).

These containers are then covered with a layer of polyethylene fabric, about 6 inches of straw, and then another layer of polyethylene fabric.  Temperatures under the fabric rarely go below 26 degrees or so — even when outside temperatures stay around -20.  Most plants come out fine — our biggest problem is that sometimes voles and mice will take up residence under the tarp and eat the plants — which isn’t a big deal unless its a research project — in those cases we will often use poisons or, more frequently, repellents.

The only thing better than this method is snow.  If we could count on snow every year we wouldn’t bother covering the plants at all.  Snow is the best insulator that we have.  Under snow temperatures rarely go below 29 degrees or so.  So, despite the traffic problems that snow causes, nurserymen and landscapers are always happy to see snow on the ground before the really low temperatures hit.