Organic Poppies Leaf Tip Burn

[Toile]

I'm growing poppies and for some reason the leaf tips of new growth are burning. Their container mix contains perlite, vermiculite, peat moss, blood meal, bone meal, potassium sulphate, dolomite and compost. I also regularly water with liquid kelp extract for micronutrients.

If I had to hazard a guess of whats wrong it would be that I've added too much dolomite and so the Ph is too high, inhibiting absorption of Fe and Cu.

Picture file is attached.