Hi, I'm new here and live in a 9B.
I'm about to plants a third tropical hibiscus. I have two others that are doing okay. They produce new flowers about other day as long as I stay on top of the deadheading. I have a new red one that I'm about to plant up against a east block wall in my back yard. Is against the wall and getting afternoon sun okay? I figured that this would be a good way to cover this unsightly wall and add color to that side.

What's the best way to plant this hibiscus in the sandy soil that we have? What should I amend/mix with the soil before and after?

I have a product called Ultrasol k Plus, it's NPK is 13.7 - 0 - 46.3. Since Hibiscus have such a great need for potassium, would this be okay to use also while planting? I have other products, yet this is the one with the highest potassium. Another I have is called "Gardner & Bloome Palm, Tropical & Hibiscus Fertilizer" 4-6-4, which seems rather weak.

Thanks.

I'd go with the weaker fert for a newly planted Hib and also use about half as much as they recommend for the first application. Don't want to burn the new roots that will be forming. The other formulation looks a bit extreme to me. Maybe try it on one of your other established Hibs first to see what happens?

The other thing they absolutely require is acid soil, and being at the base of a concrete block wall, I'd advise you test the pH of the soil before you plant. Concrete can leach alkaline stuff (lime, I think) over time with rain and watering. Since you definitely will need to water your new Hib in So.Cal you don't want to have it struggling for nutrients because of a high soil pH. If you still want to plant there, amend the soil with lots of compost and maybe some peat, and think about painting the concrete block with something to seal it against further leaching. (you could do a mural with leaves to further disguise the ugly wall . . . or just something clear)

Afternoon sun should be ok, as long as it's getting enough water when the weather is really hot.

I agree about amending the soil, and that the fertilizer you first mentioned seem really strong. BGI has a "Hibisgain" formula for hibiscus ats way more balanced I thnk something like 12-6-8. Since hibiscus like to be feed and your soil is sandy,regular feeding is a good idea, since frequent irrigation will wash fertilizer through the soil. BGI's formulas are slow release too, so that's a plus. I've not actually used their hibiscus formula, but have been a regular user of their signature product "Bougain" on my potted bougainvilleas here in TX(I'm an OC transplant, trging to grow SoCal tropicals in zone 8 north TX).Good luck!

I've had tropical hibiscus in So Cal for 40-50 years or so. I've used them against block walls and as foundation hedges along the house without any trouble. Although some recommend a slightly acidic soil, I have planted them directly into the garden with our alkaline soil and none have ever seemed to struggle. Granted, these have been older varieties. You want to make sure that you are far enough from the wall so that when mature, the hibiscus has enough "breathing room" behind. With age, the older varieties tend to get larger than what they are frequently listed as...

We actually had an old vatiety that was planted on the other side on a block wall fence crack it, (after 40 years) due to its large size. Alkaline soil was never a problem for our hibiscus in Garden Grove either. (Sunset zone 22).