I heard that some plants need fertilizing every two weeks in order to encourage flowering. I prefer organic fertilizers because I feel they provide better nutrients, however they are in granules and are slow releasing.

What is the best way for me to provide a clean, fast, organic way to fertilize the soil to encourage flowering? Should I use the inorganic fertilizer?


1 Answer 1


(Edit: My first attempt at an answer had the wrong nutrient... thanks to @kevinsky for the correction.)

Phosphorus is the key nutrient that promotes flowering.

Except that plants can't use pure phosphorus (not to mention that pure phosphorus is dangerous!), they need it in the form of phosphate (which actually describes any of a handful of different chemical compounds). Some liquid fish/kelp fertilizers are high in fast-acting phosphorus, but be careful not to overapply.

Plants can't take up phosphorus as well if the pH is too low or too high. Aim for slightly acidic -- which is what many plants prefer anyway.

In my opinion, the best approach would be to use limited quantities of fast-acting soluble phosphate like fish emulsion if you have an immediate deficiency, but to aim for a longer-term prevention of deficiency by (a) maintaining pH and (b) using an organic long-lasting, slow-release phosphate source like rock phosphate or bone meal.

  • actually it is phosphorous that encourages rooting, flowering and fruiting. Potassium is also needed for root growth and other processes within the plant cell.
    – kevinskio
    Commented Mar 23, 2012 at 14:01
  • @kevinsky: Doh! Thanks, I'll revise this later. I always mix up my P's and K's. That's what I get for referring to overly simplistic drawings to refresh my memory! (Basic premise of my answer is still the same, but the details change a lot.)
    – bstpierre
    Commented Mar 23, 2012 at 15:32
  • Does fish emulsion, rock phosphate and bonemeal need to be decomposed? Are they delicous to micro-organism? I would like to avoid bugs. I had put some slow-releasing organic granules on the surface of the soil ( the label said it can be placed either on the surface or in the soil ), and they were covered with mold or fungus some months later. Commented Mar 26, 2012 at 3:23
  • @gunbuster363: As kevinsky mentions in another answer, most phosphorous sources are not mobile in the soil. You'll want to mix it into the soil, or get it to where the roots can take it up. Liquid fertilizer will be better in this respect, but I wouldn't use fish emulsion inside if that's where your plants are located.
    – bstpierre
    Commented Mar 26, 2012 at 14:24
  • @bstpierre: I don't understand the fish emulsion part, why won't you use it? Commented Mar 26, 2012 at 14:44

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