When growing houseplants in soilless mix is it better to use an organic fish based fertilizer or a chemical one?
If you use the fish fertilizer inside you will regret the smell. It does work good and is long lasting but, the stench is too overpowering!
The best chemical fertilizers for soilless mixes have most of their nitrogen in nitrate form. They also provide soluble calcium, magnesium, phosphorus, potassium and micronutrients. Blends dominated by some combination of calcium nitrate, magnesium nitrate, potassium nitrate and urea phosphate are available at greenhouse and professional horticulture supply centers. Examples include 15-0-15, 13-2-20, and 15-5-15. Urea phosphate is strongly acidic (if it weren't, 13-2-20 and 15-5-15 solutions would precipitate calcium-magnesium phosphates) and a potassium bicarbonate solution may be needed to correct the short-term acidity. Regular garden center fertilizers (20-20-20, 15-15-30, etc.) may work well if your mix has dolomite (calcium-magnesium carbonate) or if your water is hard (rich in calcium) and your mix has vermiculite (a magnesium carrier). Just bear in mind that without a substantial population of soil bacteria, the urea and ammonium found in most soluble fertilizers will convert to nitrate form very slowly, if at all (much of the nitrogen may leak to the atmosphere as ammonia). Fortunately, most soluble complete fertilizers have potassium nitrate. -Tony
Thanks for the very detailed explanation. I'll read my fertilizer labels much more thoroughly from now on.
