Tropicals & Tender Perennials: I have a deficiency of what?, 1 by Kaufmann

Kaufmann wrote:
Several of my brugs seedlings and one plant from a cutting have leaves like this. All are in the ground. I have been playing a guessing game for the past couple of weeks, and my guesses and subsequent remedies are not producing results. The only thing I haven't tried prior to today was magnesium sulfate, which I applied today. I have very alkaline soil. I feed a good complete fertilizer once per week, and have been giving them Chelated Iron about once a month. In between, they get a treat of Liquid Seaweed or Molasses... Thanks in advance to any and all ideas :) Gretchen