I don't know too much about this process, since I use the Surya cream henna, but from what I know about herbs and what-not, you need to make an 'infusion', which is a really strong tea. You'll need to slice the beets, to expose more of the herb to the water. I don't know what form you'll get the hibiscus in, cuz I've heard of ppl using powdered hibiscus too, but if its flowers, rip them up. Okay, now, you need to put the beets in some water (the amount of which depends on how much water you usually mix in your henna), get it to a boil,
then add the hibiscus, and let it simmer for 20 min (mixing it occasionally). Strain, and let cool.
Btw, I don't know if you know about the myriad uses of glycerin
, but when I helped my mom mix up her 'real' henna a few weeks ago, I added a tbls or 2, and it rinsed out real easy. If you don't have any, I saw small bottles at CVS last week, in the first aid section, I think.