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Notes on Choosing a Fertilizer

A) Plant nutrients are dissolved in water

B) The lower the nutrient concentration, the easier it is for the plant to absorb water and the nutrients dissolved in the water - distilled water is easier for plants to absorb than tap water because there is nothing dissolved in distilled water

C) The higher the nutrient content, the more difficult it is for plants to absorb water and the nutrients dissolved in water

D) To maximize plant vitality, we should supply adequate amounts of all the essential nutrients w/o using concentrations so high that they impede water (and nutrient uptake

All that is in the "Fertilizer Thread" I posted a while back.

Let's imagine that we are going to fertilize our plants and examine how 2 different fertilizers might perform. We nearly always formulate a fertilizer program based on N needs because plants use more N than any other element. For the sake of this illustration, let's say that the plant needs 12 parts per gallon of N in the nutrient solution to prevent N deficiency, and that 50 parts per gallon of all the solids dissolved in the nutrient solution is the point at which water absorption becomes difficult & causes some degree of drought stress.

First, let's look at what happens when we supply a 3:1:2 ratio fertilizer - let's say we use 12-4-8 to supply the 12 parts of N needed. Because the P and K goes with the N, 12 + 4 + 8 = 24 parts of fertilizer applied. We know there are substantial other dissolved solids (many are nutrients, but some are unusable elements) in the solution besides the NPK, so let's set that amount at 12 parts. You can see that we now have the 24 + 12 parts or 36 parts of total dissolved solids in the solution, and we're still well under the 50 parts where water uptake becomes difficult.

Now lets shift gears to a 1:1:1 ratio fertilizer that has 12 parts of N. Obviously, it has 12 parts of P and 12 parts of K, too, so we're applying 36 parts of fertilizer to satisfy the same plant's need for 12 parts of N. If you add together the 12 parts of other dissolved solids like we did in the 3:1:2 illustration above, we are applying a solution of 48 parts per gallon to satisfy the need for 12 parts of N. What gives here?!

Looking deeper into this particular illustration, we can see that if we make a minor mistake and apply too much, or there are even a small amount of residual dissolved solids in the container solution, we are going to go easily beyond the safe 50 parts per gallon. On the other hand, if we reduce the amount of fertilizer applied so we're not dangerously close to the stress causing 50 parts per gallon, we fall below the 12 parts of N needed and have created a N deficiency.

The devil in the details tells us that the key to this second illustration lies in the fact that we unnecessarily applied much more P and K than the plant could use by using the 1:1:1 ratio 12-12-12.

This was simply an illustration to help you understand that even though plants have a tendency to take what they need and leave the rest, 'the rest' CAN have a profound effect on plant vitality/nutrition simply by being there, even though unused.

While using a 1:1:1 fertilizer as your 'all-purpose' choice is certainly possible, people have been doing it for years, using a fertilizer that is very close to what the individual plant is known to use (and an extremely high % of plants use closer to a 3:1:2 ratio than any other readily available blend) greatly widens the margin for application error by allowing you to apply at lower rates, and greatly increases the range between deficiency and toxicity levels of many of the elements in whatever fertilizer you choose.

Consider that perhaps instead of arbitrarily choosing a fertilizer without due consideration and using it as YOUR 'all-purpose' and 'the one I always reach for' blend, we might just be better off if we look for a fertilizer already labeled 'All-Purpose'. The odds are 3:1:2 that it will better suit your needs.

Al

Comments (13)

  • 17 years ago
    last modified: 11 years ago

    OK, another great explanation of proper fertilizer applications. I am a more is better person so I have to restrain myself when it comes to watering and fertilizer. Thanks so much Saint Al. Oh, and Merry Christmas!

  • 17 years ago
    last modified: 11 years ago

    Thanks Al. This helps. filix.

  • 17 years ago
    last modified: 11 years ago

    Thank you Al for all your help and great knowledge.
    Happy Holidays!

  • 17 years ago
    last modified: 11 years ago

    What a great thread! Thanks Al, for the very helpful information and explaining it so well, easy to understand. Sometimes I get lost when it becomes too technical, LOL...

    It helps me so much and so many others I'm sure.

    Merry Christmas!!

  • 17 years ago
    last modified: 11 years ago

    Thank you all for the kindness in taking the time to say thanks. It's appreciated. I know that much of what I write has a technical bent to it, even when I try to simplify it as much as possible. It's not that I try to MAKE things technical; it's just that much of what I choose to write about IS technical by nature.

    I hope I never make anyone feel small for asking questions about subjects others might have a more complete understanding of. You can always ask any question you want - if I know the answer, I'll do my best to help, or direct you to where the answer can be found.

    Thanks to all for the Merry Christmas wish. As I grow older, I think it gets easier to keep my heart where it should be at Christmas time, so please allow me to return your wishes with my own, in the hope you'll feel the spirit and sincerity in them. ;o) Merry Christmas.

    I'll even leave you with a little something to chew on.

    "And the Grinch, with his Grinch-feet ice cold in the snow, stood puzzling and puzzling, how could it be so? It came without ribbons. It came without tags. It came without packages, boxes or bags. And he puzzled and puzzled 'till his puzzler was sore. Then the Grinch thought of something he hadn't before. What if Christmas, he thought, doesn't come from a store. What if Christmas, perhaps, means a little bit more." ~Dr.color> Seusssize>

    Al

  • 17 years ago
    last modified: 11 years ago

    Thanks for the info. What is your feeling on plants like plumeria? People always talk about giving fertilizers high in P to promote blooming, but my personal feeling is that this does not have this effect, and in fact just deprives the plant of nitrogen.

  • 17 years ago
    last modified: 11 years ago

    I agree, and what I said above illustrates exactly what you're saying. There are no plants I know of that use anywhere near the amount of P as they do N (1/6 is the norm). It makes no sense to me to have more P available than N unless you are targeting a VERY specific growth pattern; and then the P would still be applied in a reasonable ratio to K.


    Al


  • 17 years ago
    last modified: 11 years ago

    Al,

    One quick question, please...

    You wrote "distilled water is easier for plants to absorb than tap water because there is nothing dissolved in distilled water"

    I was wondering about "rain water" does this fall in the same/similar catergory as distilled water or not? I ask because I have a rain barrel that collects rain water from my roof gutter, and I use this for my container plants (whenever I have it).

    Thanks again for your help, I love Dr Seuss!!

    N

  • 17 years ago
    last modified: 11 years ago

    Rainwater and melted snow are almost the same as distilled water, and for the purpose of using it to irrigate plants, you can consider it the same. Generally, rain has a pH slightly under 6.0, mainly because atmospheric carbon dioxide dissolves in the droplet to form minute quantities of carbonic acid, which then partially dissociates, lowering the pH. In some desert areas of the country, airborne dust contains enough calcium carbonate to counter the natural acidity of precipitation, and rainfall can be neutral or even alkaline. Rain below pH 5.6 is considered acid rain and occurs often downwind from industry that emits sulfurous compounds into the air.

    Rainwater rocks, ;o)

    Al

  • 17 years ago
    last modified: 11 years ago

    During my dry season I drip irrigated crops with well water & always could see the salts accumulating on the soil. The geologic composition in the area was
    called "caliche" - a mineral & calcium formation risen from the sea.
    A rogue rain would perk the plants up noticeably, even though watering was adequate. If it rained enough the salt stains around the vegetables would be purged away.
    The minute change in pH would give the roots a chance to function under
    their ideal conditions.
    The refreshed scent out in the field was always envigorating & made
    me think of the earth breathing. Or to go forum politicly correct - maximum aeration follows a proper watering when good drainage exists.

  • 17 years ago
    last modified: 11 years ago

    Thanks for the clarification and explanation Al :o)

    I was very happy when I finally got my rain barrel, it was one of the best investment I made for my plants, they love it!

  • 17 years ago
    last modified: 11 years ago

    I worked at a nursery a few years ago with well water PH in a range toxic to most plants. They installed a storage tank with the ability to correct the PH but it made the water not fit to drink, requiring bottled drinking water. Al

  • 17 years ago
    last modified: 11 years ago

    Bump.

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