4/17/2021 – Year before last we had four Hibiscus along the meter/switch-box wall and that winter three of them were killed by the cold temperatures. One survived, came back, and did ok last year. This winter again almost killed it but it has leaves coming up out of the mulch. Researching what to feed a hibiscus led to this page. The following was extracted from there.
When looking for a fertilizer for hibiscus, look for this ratio: Medium – Low – High. If all three numbers are the same, as in most “Superbloom” formulas, there is too much phosphorus and too little potassium for hibiscus. The ratio we have found to be the best is the one we use in our HVH Special Blend Fertilizer: 17-5-24. This is the fertilizer we developed for our own hibiscus, after much trial and error.
When you look for a fertilizer, also look at the “minor elements” in the formula. These are other minerals that hibiscus need in small amounts. Make sure you find a formula that includes at a minimum copper, magnesium, and iron in a soluble or chelated form. Ideally your fertilizer will contain several other trace minerals too.
We have 15-0-15 and some 0-0-66. As their blend has about 30% more potassium than nitrogen we need to add 5% to the 15-0-15 to make 15-0-20. So, if we take 1 lb. of 15-0-15 it would have 0.15 lbs of potassium. We need to add 0.05 lbs of potassium. So, Wt.Needed x 0.66 = 0.10. Wt. Needed the = 0.10/0.66 = 0.15 lbs. = 2.4 oz. When mixing the blend in a quart canning jar I added a bit much 0-0-66; i.e. 3 oz. So, that is about 25% more than the exact value making for a 15-0-21 mix.
Shook the jar well. Raked back the mulch from around the new leaves and sprinkled about a cup around it. Pulled the mulch back around it.
Within two hours we had more gentle rain.