I am only guessing Joanna means water-soluble fertilizer used according to the directions on the package.
My gardening neighbor was my teacher and she told me a little bit of ES with every feeding is better than a lot once or twice a season. For those not as faithful with spraying as Joanna, sprinkling a few tablespoons on the earth where large clematises grow has proven to do very well, along with aged manure and aged compost.
