I just read so many different dosage combinations for tropical hibiscus and fertilizing....geez...can anyone please tell me straight forward what I should be using??
Hibiscus is one of the very few plants I treat different than others in containers. I use 3:1:2 ratio fertilizer (like 24-8-16, 12-4-8, or 9-3-6) on almost all my containerized plants. Well, actually, I use it on hibs too, but with a twist. Hibiscus is not overly fond of P(hosphorous), but it does like K (potassium). It likes a fertilizer low in P but higher in K than most plants, so something that supplies at least as much K as N - a fertilizer with a 3:1:3 or even a 3:1:4 RATIO.
Since you should have on hand a 3:1:2 ratio fertilizer for almost all your container gardening needs anyway, it's quite easy to turn your 3:1:2 ratio fertilizer into a 3:1:3 ratio by adding a little potash or Dyna-Gro's Pro-TeKt 0-0-3 (better choice because it has silicon in it) to your fertilizer solution when you fertilize.
It's best to avoid 1:1:1 ratio fertilizers like 20-20-20 or 14-14-14 because they supply much too much P in relation to N or K; and it's important to avoid all bloom-booster fertilizers and fertilizers with a middle number as high as or higher than either the first or third numbers (N or K).
In the end, you can use any 3:1:2 ratio fertilizer (I like Foliage-Pro 9-3-6 best) right from the package with good results, but adding a little extra K to that strategy would be an improvement and please the plant.
Its funny when I use 20-20-20 on my hibs they turn yellow and drop some leaves. But after a while they put out new growth and begin to green up and flower like crazy! Its the only fertilizer I have so I used it:-( But they look good now.
Al...thanks for the explanation, however still don't understand why the plant wouldnt appreciate a higher P to encourage more bloom??
Most growers erroneously believe that high P levels promote blooming, but such is not the case. In addition, Hibiscus stores P and needs very little. P can easily become toxic to Hibiscus, with the stress causing A) poor growth, B) aborted or poor blooms, C) high pH that additionally stresses the plant due to poor nutrient solubility, D) antagonistic deficiencies of other nutrients E) other issues related to stress, like disease and insect infestation resultant of a suppressed metabolism.
Taken from an abstract in Hort Science (I've edited it to make it more readable):
A series of experiments were undertaken to determine the effects of nitrogen (N), phosphorus (P), and potassium (K) concentrations and N:P:K ratio on flowering and vegetative growth of two herbaceous perennials, Hibiscus moscheutos L. (hibiscus) and Rudbeckia fulgida var. sullivantii Ait. 'Goldsturm' (rudbeckia). Plant growth and flowering of both hibiscus and rudbeckia were influenced by concentration and ratio of N, P, and K. When N was held constant at 100 mg/L, 4:1 N:K and 16:1 N:P were optimal for growing hibiscus [that's 16 times more N than P], whereas higher K concentration and lower P concentration were required for optimal growth of rudbeckia. However, when holding N constant at 100 mg/l and varying both P and K in the fertilizer solutions, higher P and K concentrations and a 2:1:2 N:P:K ratio best supported hibiscus growth, whereas 3:1:2 N:P:K was needed for growth of rudbeckia. Finally, when both N concentration and N:P:K ratio were altered, optimum growth of both hibiscus and rudbeckia was achieved at similar and lower P and K concentrations - an 8:1:2 N:P:K ratio was optimum for production of both hibiscus and rudbeckia, although 12:1:2 N:P:K produced similar growth of rudbeckia.
The short answer is, the higher levels of P don't encourage blooming in hibiscus because they are being offered at toxic levels. Also, it's much more effective in almost all cases to reduce the N supply instead of increasing P to promote blooming. Reducing N curtails vegetative growth, which forces the plant to spend it's energy on producing reproductive tissues instead of vegetative, so the result is more blooms/fruit.
Assuming you have the right light/temp, the keys to bringing along great hibiscus in pots are - an appropriate soil, YEARLY repotting (not just potting up), and an appropriate fertilizer - one that is LOW in P.
Al, again I appreciate your time educating me on this issue. I do have a better understanding now, just a lot of info to absorb. Sad part of this is I called two local garden centers asking specifically for hibiscus fertilize and each told me to use all purpose/general fertilizer!! I tried to briefly educate them only for them to dispute what I was saying....grrrrrr. Oh well, thank you for sharing valuable info!
You can use Miracle-Gro All-Purpose 24-8-16 and it will be fine ..... or any of the other 3:1:2 ratio brands. Peter's, Schultz, Jacks, all make 24-8-16 soluble. Miracle-Gro makes a 12-4-8 liquid; and MY favorite for practically everything I grow in containers is Foliage-Pro 9-3-6, another 3:1:2 ratio fertilizer. If you want to fine tune any 3:1:2 ratio fertilizer specifically for hibiscus, you'll just need to add a little muriate of potash (potassium chloride). You can get it at Ace Hardwares @ $4.50/4 lbs. If you're fertilizing using a full recommended strength solution, add 1/2 tsp/gallon of fertilizer solution. I'd recommend that you use a half strength dose twice as often as suggested.
Let me know if you have any questions.
I use potting soil with some added manure then eb stone sulphur potassium and magnesium. Nitrogen in moderate amounts, very little phosphorus and lots of potassium. During the season I scratch in the eb stone fertilizer and worm castings