NPK ratios?

Tue, 29 Jan 2008 19:54:36 PST
Good questions, Robert. I will share a few things I have learned over the
years and hopefully you can apply some of them to your situation.
A few years ago a friend told me that his agriculture advisor told him that
unless you are growing turf or bedding plants the ratio should be about
1:2:2 or 1:2:3. Otherwise you are wasting the N or possibly risking
toxicity-- in your case it could be that there would have been plenty of N
for your Hipps if you used half the ratio amount of your formulation,
increasing the dilution rate as necessary. Since I learned this and also
observed the results my friend got using such a formula with his orchids,
succulents, etc., I have switched to a rather strange-sounding 5-11-26
hydroponic formula made by Grow More. A bag of about 40 lbs costs about
25.00. Since using it on a very wide range of plants, including aroids,
orchids, amaryllids, succulents, ferns, etc., I am very happy with the
results. Plants bloom better than before and growth is strong and never
lush. I don't grow commercially so am not concerned with "pushing growth".

Yes, there is something to the ratio situation that is important here but I
don't know how it works exactly. The three major components work together
chemically to some extent (versus independently), along with the minors, and
the interrelationships between them and with the soil (pH, cation exchange
capacity, etc.) are complex. If you are blessed with good water quality you
have already cleared some major hurdles.

As far as rates I apply N at between 150 and 200 ppm or a little higher; I
think it could go quite a bit higher, at least occasionally, without any
harm. I fertilize with nearly every watering and so keep the concentrations
low generally-- but note that at 200 ppm N for this formula the K is over
1000 ppm! Once in a while I apply calcium nitrate separately to supply
calcium, especially to epiphytes.

A word about nitrogen. Many years ago Fred Meyer told me that amaryllids
like Hippeastrum and many others (but not so much hardier fare like Crinum
or Narcissus) resent N in the form it typically appears in fertilizers: as
ammonia or urea nitrogen. I made the switch to orchid fertilizers such as
Dyna-Grow years ago just to get N comprised of mostly nitrate nitrogen, with
a small percentage of ammonia nitrogen. I bloomed some difficult bulbs when
I did this, plants that had not flowered for 10+ years previously
(Hippeastrum parodii, Paramongaia, etc.). Nitrate nitrogen is worth the
moderate extra cost in my view and it is not difficult to find brands that
use it.

You should not have to worry about any salt build-up unless you are not
watering thoroughly or your fertilizer is too concentrated and applied too
often. I try to double water plants every time I water and have very little
problems with excess salts.


On Jan 28, 2008 9:21 PM, rdjenkins <> wrote:

> 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.
> Robert.
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