NPK ratios?

Mon, 28 Jan 2008 21:21:15 PST
I have been wondering about the various ratios of the three main nutritional elements in prepared fertilizers and have a few questions that I hope someone can help me answer or point me to where I may find them. 

This past summer,  I switched to a brand-name product to feed my Hippeastrums. The ratio I chose was 24-8-16. I had excellent results. 

I have two H. papilios in bloom just now: one has three scapes and the other has two. I have had both bulbs for just over two years and they are the common Dutch run. Both have a scape with three (yes!) blooms in the peduncle. 

Obviously, the lower proportion of P has had no negative effect and the higher N content only helped grow the great foliage and size up the bulbs. Contrary to some warnings I received, the foliage wasn't unnaturally lush, tender or weak, but was as healthy and as strong as I have ever seen it. And contrary to what is often promoted for other non-bulbous plants (higher P percentage) and might seem to be called for in Hippis in what seems to be a logical and sensible way, my plants had everything they needed to flower better than ever with the higher N and lower P ratio.

I know that applying N alone can "push" green growth to the expense of floral production in many annuals. One question I have about blooming annuals is how much "pushing" occurs as a result of a higher proportion of P on the blossoming of annuals? This is more for general interest, since I am really more concerned with Hippis.

For instance: If I am feeding a plant 5-15-5, is there something in the 1-3-1 *ratio* that "pushes" flowering more than 15-15-15, since the plant is getting the same amount of P in both cases? Would it be a matter of the plant making use of the more abundant element in the 5-15-5 feed, whereas with the 15-15-15, the plant's energy is divided between green and flower, so it might have less abundant flowers?

Back to bulbs: As I understand it, the various ratios for blooming plants comes out of chemical analysis of the entire plant to find out where the N-P-K ends up (as well as observations of differences in color, strength, and quality of different plant parts.So, blooms showed higher P content and for better blooms more P was prescribed. 

How much is "too much"? That is, from this past season's results, 24-8-16 at a constant dilute feed was obviously good enough to supply what my bulbs needed to grow and produce buds, could it still make use of more of any element? When is a plant's mouth full and unused elements just stay in the soil unused and possibly building up to toxic levels? 

Another question:  Do the different proportions make a chemical difference in the bulb itself or is it all one form that ends up in different concentrations depending on target?

I hope you can understand, perhaps between the lines, what I am wondering about. Since all the different ratios of NPK cost the same by-the-box for me, it isn't a matter of paying for something my plant can't use, but if I was preparing my own, cost might or might not be a factor in adding essentially unused levels of nutrients. 


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