I just finished putting about 130 gallons of mixed castor oil and water around my roses and elsewhere in the beds, where voles might burrow their way through the wood chips and mulch. If you missed my blog post about voles and the damage they inflict on roses during the winter, check it out right here: http://theminnesotarosegardener.blogspot.com/2012/10/voles-and-roses.html
As I began mixing the castor oil (which I got at Wal-Mart @ $2.65 for a six ounce bottle), I was frustrated at how it wouldn't mix with the cold rain water from my cistern. I put one 30 gallon batch around the roses and it was clinging to everything; my gloves, the can I mixed it in, and the sprinkling cans I was using to pour it around the roses. Then the lights went on. I had forgotten to put the liquid detergent in the mixing can @one teaspoon per gallon! As soon as I did that, the castor oil dissolved perfectly and the job became much easier.
So, here again is the formula for putting castor oil around your roses: Use one or two teaspoons of castor oil and one teaspoon of dishwashing detergent per gallon of water. Pour (or pump) the mixture around every rose so that it can soak into the dirt or mulch a couple of inches. I probably put around half a gallon around each rose (or a little more) and then I pour it around between the plants and around the edges of the beds, i.e. anywhere that these little chewing monsters might burrow in the wood chips and mulch.
Castor oil is cheap, so I use more rather then less of it (i.e. two teaspoons per gallon rather than one). Note: Ten ounces of castor oil gives you approximately two teaspoons per gallon mixed in a 30 gallon trash container.
If you haven't read the article and watched the video from New Hampshire Hostas, about using castor oil to control voles, be sure to take a look at it: http://www.nhhostas.com/organic-vole-control.htm . The video is a little long-winded but interesting. The mixture formula is on the website as well.
This is prime time to put down castor oil. As the ground freezes, the voles start burrowing around the beds to find the tastiest food supply for the winter: your roses!
So, don't make same the mistake I did and forget to put the liquid soap in your castor oil mixture. And good vole hunting!