Diana and all, I agree with Diana --- my understanding from 30 years ago is that ammonium nitrogen is absorbed under all conditions relatively poorly by plant roots, compared to nitrate. On the other hand, ammonium is the preferred form of nitrogen for all fungi and many bacteria. Len Doran drove this point home to those of us whom he undertook to coach: Ammonium feeds the pathogens trying to kill your bulb, nitrate feeds the plant! In Narcissus poeticus (Vickery et al, 1946, cited in Rees) they found that the plant tissue analyzed as follows: Bulbs grown on nitrate as source of nitrogen, 15.9 g N per 50 bulbs Bulbs grown on ammonium as source of nitrogen, 14.0 g per 50 bulbs. My bibles, (post Doran), have been "The Growth of Bulbs" by A. R. Rees, pub. by Academic Press, New York & London, 1972 and "The Physiology of Flower Bubls" by A. de Hertogh and M. Le Nard, pub. by Elsevier, Amsterdam & New York, 1993 The point made by Doran was the same as that made by Rees: Bulbs need nutrients in the approximate ratio the nutrients occur in the healthy bulb tissue. Plants are also limited by any nutrient that is present in significantly less than needed levels. Unfortunately, only Gladiolus, Lilium, and Tulipa have been studied in detail. As a general thing, the ratio of N, P, and K in plant tissue is about 4 N to 0.3 P to 2 K. The precise ratios can vary not only from genus to genus but from cultivar to cultivar. The question of the effects of nutrient ratios on efficiency of absorption is not resolved so far as I can recall -- or my knowledge may be decades out of date. I am not aware the N, P, and K affect each others absorption rates. Mg (magnesium), Ca (calcium) and K (potassium) are similar in ionic charge (Mg and Ca) and in size (Ca and K) and are said to be able to interfere with each other's absorption. This alone might indicate that applying calcium at a different time than magnesium would increase the effectiveness of the applied nutrients. Loading the fertilizer up with phosphate is relatively harmless in soilless growth medium. In soil, excess phosphate can tie up iron, calcium, and probably a couple of the trace elements, depending on the ambient soil pH. Phosphate is of course essential for plant growth, but in significantly smaller amounts that N and K. I've never understood where people are coming from when they recommend high phosphate fertilizers; this just does not make physiological sense to me. Jim Shields in cold central Indiana (USA) At 01:12 PM 1/30/2008 -0800, you wrote: >It is also my understanding that nitrate nitrogen, in the form of potassium >nitrate or calcium nitrate, is better absorbed at lower temperatures, so >this is important for those bulbs that grow during the winter. The >formulation I use has both ammonium nitrite and potassium nitrate, but the >main ingredient is potassium nitrate. > >Diana >Telos Rare Bulbs ************************************************* Jim Shields USDA Zone 5 Shields Gardens, Ltd. P.O. Box 92 WWW: http://www.shieldsgardens.com/ Westfield, Indiana 46074, USA Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA