Sunday, August 26, 2012

Potassium: A Special K-Ration Feast For Your Roses

Providing a Potassium (“K”) feast for my roses in the six weeks prior to the first hard freeze of early winter has been an important part of winterizing my roses for over 20 years.  And yet, few, if any, rose-gardeners seem to know anything about it.  I have noted with pleasure the large number of rosarians reading my blog, not only in the U.S. and Canada, but also in other northern climates, such as Russia, Germany, France and the U.K., all of whom stand to benefit from learning this winterizing trick.  It doesn’t have to get as cold as Minnesota in your rose garden for this to be useful!

Here is a quote from Burpee’s American Gardening Series book Roses, by Suzanne Frutig Bales, which is the only place I have read about using Potassium for winterizing:

“Potassium is an important mineral for sturdy stems and foliage.  Weekly feeds of a gallon of liquid potassium (1 tablespoon of muriate of potash (0-0-62), dissolved in 3 gallons of water) per bush, or a granulated feeding of potash magnesium (0-0-22), during the six weeks before the bushes go dormant, will give the bushes an additional boost for winter, extending their hardiness into another hardiness zone, perhaps two.  Excess potassium, when available in greater amounts than nitrogen and phosphorus, is known as the ‘potassium feast’.  It will block the growth-promoting effects of nitrogen and phosphorus, hardening the canes in time for winter.” (emphasis mine)

Here in Minnesota, I begin my roses’ potassium feast in the second or third week of September.  That takes me through the end of October or beginning of November, which is about as late as I want to go.  There have been years, perhaps when I started a little too late, that I’ve had to thaw out my hose or turn off my water and turn it back on again in order to complete the sixth treatment.  You have to be the judge of when to get started in your area, but my advice is don’t wait too long, because it’s better to be too early than too late with this. 

I use Muriate of Potash (0-0-62) that I get in 50-pound bags at a local farm-supply store (Waconia Farm Supply near Minneapolis).  By the way, I define a farm supply store as a place that sells bulk fertilizers to farmers, not someplace that sells bird-seed to bird watchers.  A 50- pound bag of Muriate of Potash lasts me five years or more, because you really don’t use that much in a year (i.e., one TBP/three gallons of water).  I mix it in a clean, 60-gallon trash container and apply it with a sump-pump, through a hose and watering-wand.  This little trick of using a sump-pump for applying liquid fertilizers is a huge work-saver throughout the growing season.  I read about it in the Twin Cities Rose Club Newsletter several years ago. 

The Muriate of Potash I get from the farm-supply store is a reddish, crystalline substance that doesn’t dissolve as easy as most liquid fertilizers.  I use as much water pressure as I can muster, through a nozzle turned on all the way, to get it dissolved.  The sump-pump goes in after the tank is full.  It also makes your clothes red, if you get it on you (as I always do), but it washes out eventually. 

After about the third-week’s application, you will begin to notice that the canes of your roses are turning a pretty shade of deep red, so you can actually see them hardening-off for the winter, which is fun to watch.  When I tell people that I think the potassium feast actually does extend my roses’ hardiness into another USDA zone, they usually scoff at me.  All I can tell you on that score is that I haven’t lost a single rose to winter-kill in many years and I am not an aggressive winter protector.  (See my recent blog post: ). 

I also believe that this method of winter protection is particularly interesting for northern gardeners worldwide, as we see the continuing effects of climate change in the rose garden.  (See my blog post of several months ago: ).
While putting on liquid-potassium for six weeks seems to be a lot of extra work in the rose garden, I think it actually can reduce the overall work of winter protection, once you gain confidence using it in your own garden. 

I would really like to hear from you, if you take my recommendation and decide to start using potassium.  Please leave me a comment below or, better yet, send me an e-mail to: .  If I don’t already have you on my blog distribution list, I will be happy to add you, as well as answering any questions you may have about growing roses in the northern hemisphere.

 Jack Falker in Minneapolis


  1. I have done this for several years. I also give each of the rosebushes a couple of tablespoons of Super Phosphate late in the season before they go towards dormancy. It moves slowly in the soils so also helps them through winter and with the boost for spring. Good blog you have here!

    1. Thanks Stan... Good idea on the Super Phosphate; I will put it out in a follow up blog. Send me an e-mail to and I will include you on my blog mailing list.