Broccoli leaves turning purple
I have a few small Broccoli di cicco transplants that I raised from seed that I planted in my raised bed about 2 weeks ago. Yesterday I noticed that a few of the lower leaves were turning purple. The newer growth looks fine, although the plants are not growing very quickly. My raised beds are filled with a pre-made mix that had lots of organic matter and expanded shale. Drainage does not appear to be an issue. I haven't tested the ph of the bed.
I've heard with tomatoes that purple on the leaves can be a phosphorous deficiency. Could this be the same thing?