First off, I'd tell you to absolutely stop diagnosing individual deficiencies. Especially if you haven't had soil or plant tissue tested. Since we all know that's typically expensive - sometimes prohibitively so - let's just go on the assumption that you haven't done that.
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Secondly - have you been supplementing anything else? Nitrogen? Calcium? Magnesium?
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What is your typical feeding regimen? What were they on, before they got to this point? How often? What's your soil pH? More info, more info, more info... If you have had this problem with other plants, as well, then you have a definite problem, and you need to get to the bottom of it.