Using the word "bulbs" loosely here... Gene asks "How do we know that K is a key bulb nutrient? Are there references?" When I sent a soil sample for nutrient analysis to Spectrum Analytic, they offered to provide recommendations for fertilizer based on crop. I explained my "crops" were Aristea to Zephranthes and did not expect them to actually look up references. I was impressed at the research they did. Where possible they provided nutrient requirements to the genus level, and for some just to the family level. Of course my species allium are not going to need the same nutrients as commercial onions (where at least they distinguish between onions grown for big bulbs versus "green onions" grown for foliage). I was impressed they would do research for one backyard baggie of soil. I did warn them ahead of time that I am not a farmer and not a "real" customer. I grabbed a few screenshots from the reports in case this sort of information is of interest. The complication here is these recommendations are based on my backyard soil, not your potting mix. The only information useful here is the sort of nutrients there exist references for and the level of specificity. See for example: http://goo.gl/t88fB/ If you want to try it with your own soil or potting mix I recall it cost around $60 for the tests I ordered. - Gastil