Right now, as the ground freezes, is the perfect time to protect your roses from vole damage during the coming winter. The correct approach is two-pronged: First, voles are deterred by castor oil applied to the ground in areas where they burrow, so applying castor oil, in the right dilution as winter sets in, should be your first line of defense. Next, the strategic placement of vole baits to kill those varmints that might make their way through your castor oil deterrent is your second line of defense.
Today (November 13th), I made my application of castor oil, which I buy inexpensively from Wal-Mart in their health and beauty area. It is also available from several vendors on line, if you do not have access to a Wal-Mart store. Please note that it is important to mix castor oil with liquid detergent as you dilute it with water in the proportions given below. The soap helps the oil dissolve in the cold water so that it doesn't stick to your sprinkling can. I inadvertently mixed some once, without the soap, and it gets very sticky and messy.
I discuss this two-pronged approach very thoroughly, plus much more, in my October 2012 blog post: "Voles". Here is the address of that blog:
http://theminnesotarosegardener.blogspot.com/2012/10/voles-and-roses.html
And here are a couple of excerpts from that blog post:
Castor Oil: This is the most effective solution I have found. Voles really don't like castor oil; apparently, from what I have read, it makes them sick, and they avoid an area on which it has been applied. Mix one or two teaspoons of castor oil (I use more rather than less) and one teaspoon of liquid detergent, per gallon of water, and apply it liberally around the bases of your roses and generally around your rose beds, where the voles might travel/burrow in the winter. The best time to do this is in late Fall, when the ground is lightly frozen, just before putting your final mulch or leaf cover around your roses. Around here, that would be in mid to late-November. I mix it in a 30-gallon trash container, pump it out with a sump pump, and apply it with a hose and watering wand, exactly like I do liquid fertilizers and potassium. You can also use a sprinkling can to apply it, if your garden isn't too big.
Note: Two teaspoons of castor oil per gallon in 30 gallons of water amounts to 10 ounces of castor oil. Wal-Mart's castor oil comes in 6 ounce bottles, so it takes a little more than 1 1/2 bottles for a 30 gallon trash can of the oil/soap/water mixture. A friend in Wisconsin reports that he is using one tablespoon (3 TSP) of castor oil and one tablespoon of soap per gallon and that's just fine. In this case, more is better to deter these little monsters. In fact, in 2017, I just used 2-bottles (12 oz.) of castor oil and 30 TBP of dish soap per 30 gallon can, just to keep it simple. This should give you some idea of how much to buy.
Pour the castor oil and soap into the 30 gallon can and then add water, stirring while you go. I also think it goes on just as easy with a sprinkling can as it does with a pump, so that's what I'm using now.
Rodent Baits: Killing voles is desirable, before they over-run you, but this is a touchy subject because rodent baits can also affect other animals, like neighborhood cats and dogs. The common rodent bait that you find in most stores is an anti-coagulant poison, which, when eaten a couple of times, stays in the intestines, causes massive internal bleeding and kills the animal. I used it in my rose beds for years, without thinking, until about five years ago when we got a new kitten and he managed to find a mouse or vole that had eaten it, in among the winter-protected roses. I will save you the terrible details, but it resulted in a very large emergency veterinary bill.... After that experience, I went to work researching what other non-coagulant rodent baits might be on the market, and I found one. The brand name is "Eraze", made by Motomco, the same company that makes the anti-coagulant baits. The active ingredient in this one is Zinc Phosphide, which is nonetheless a poison, but acts in a different way, killing small animals immediately after ingestion. There are conflicting opinions on this, but an article by Michigan State University indicates that it is less lethal to larger animals, such as cats and dogs, because their normal reaction after ingesting it would be to regurgitate it rather than digest it.
I have written a couple of other articles about vole protection, which contain several other comments and ideas. Here is my September 2013 post:
http://theminnesotarosegardener.blogspot.com/2013/09/voles-and-castor-oil.html
As always, please send your questions or comments to: jfalkersr@gmail.com .
Jack Falker
November 13, 2015
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