Thank you for contacting Ask Extension. So from your question, are you asking for what you can put down for the Potassium but not increase the Nitrogen, correct?

Thank you for contacting Ask Extension. I did not get a response from the question I sent to you on 4/17, so I will proceed with the information I can give you. There are many products out on the market with only Potassium in it. Espoma Potash and Muriate of Potash are both 0-0-60, Some are 0-0-48. Google Potassium fertilizer and you will find it. I agree about not putting down a nitrogen product. I also would not put down a phosphorus fertilizer either because that is used for root development and can also accelerate root production. But once you have the scale under control, I would add potash and phosphorus to help your hemlocks have a balanced fertilizer. 

I am not sure what MSU recommended on the amount to apply, but I would not do it all at once. Put 1/2 down now, then the other 1/2 by the middle of May. 

Here are a few references for you:

https://www.umass.edu/agriculture-food-environment/sites/ag.umass.edu/files/fact-sheets/pdf/organic_fertilizers.pdf

https://cmg.extension.colostate.edu/Gardennotes/234.pdf