I vaguely remember my mom talking about henna when I was a child and I keep reading how great henna is for your hair in terms and strengthening and thickening it. AND I'm about tired of looking at these grey hairs on my head...SO, I've been doing a little research on henna. I found a (FREE) eBook on hennaforhair.com and it's packed full of information! There's SOOO much to henna that it really is overwhelming, though...
What brand to buy...
How long to leave it in...
What to mix it with...
Blah.
Blah.
Blah.
I think this article from wisegeek.com does a good job of explaining the basics of henna without getting too "techincal." 
What is Henna?
Henna dyes hair, skin, and fabric organically, similar to a black tea dye. Henna is extracted from a tree by drying and grinding leaves and stems. The greenish powder, when mixed with an acidic liquid, makes a temporary red, brown, or orange design on a porous surface. People use henna in ritual skin painting, called Mehndi, for birth and marriage celebrations. Western cultures have adopted henna to make temporary tattoos and organic hair dye.
The henna tree, Lawsonia inermis, grows in hot, arid regions like North Africa and India. For centuries, people ground the foliage of the plant into a powder to dye cloth and skin. The strong pigment, lawsone, actually temporarily stains the skin. Lawsone is a tannin; tannins are also found in wine and tea. They infuse porous surfaces with a darker pigment, but do not chemically alter the surface permanently.
Henna works because lawsone is absorbed into material like hair and skin. You mix the powdered henna into a mud, using hot water, lemon juice, vinegar, or other acidic additives. An acidic mixture strengthens the dyeing properties. Then you apply the henna mud to a surface like the palm of your hand, bottom of your feet, or anywhere on your body. Leave the mud on for as long as possible, up to 48 hours. When it dries and crumbles off, the skin will have darkened to auburn, orange, red, or brown.
Depending on the fineness of the paste, you can apply henna with a tube, like icing a cake. With a lot of coordination and care, people can achieve intricate designs full of scrolls, swirls, paisley outlines, and dots. Henna tattoos create temporary bracelets, motifs, emblems, or words. In traditional Mehndi, Muslims and Hindus decorate the skin of those participating in special ceremonies, such as a wedding or circumcision, in places like Indonesia and India.
Dying with henna is entirely temporary. Hair dye may last up to six weeks, but skin dye will probably not stay visible for more than a week. This is because the dye has only sunken into the uppermost layer of dead and dying skin. When your skin flakes off through natural exfoliation, it will be gradually replaced by fresh skin of your natural color. Henna hair dye will also slowly fade away to your hair's original color, but will not leave any lines or stripes like synthetic dye.
I finally used the cassia obovata on my daughter's hair and I loved it. It is a pain to wash out though. It's worth it since it's only once a month. I also picked up some hibiscus powder on ebay. LHDC, let me know if you want to try it and I'll send you some because I got a pound and it's a lot!!! Q
LHDC: You are too sweet, Q! I'm going to have to try that stuff on my oldest's hair. It is so fragile. Thanks for the update!
Posted by: Queeny | March 30, 2009 at 08:50 PM
I love Henna, I'm going to add indigo so that my grays are not so bright red my next henna. It makes my fine hair strong and thicker and shiny, and it covers grays... I do a glossing which makes it easier to wash out.
Posted by: AtlantaJJ | March 28, 2009 at 10:49 PM
hey girl --- to cover your grey, I would recommend the bundle for "African Hair" on the hennaforhair site. Keep it simple and just add water and a little ACV or orange juice. For just conditioning properties, I just use 2 cups plain yogurt or sour cream (full-fat)and 120g or so of henna/indigo powder..
LHDC: Hi, Lina! I will have to check it out! That sounds like something that I'd be interested in. Lord knows at the rate these greys are coming in I'll be full gray by the time I'm 40 (and that's not too far away!)
Posted by: lina40 | January 31, 2009 at 10:47 AM
I want to get rid of this grey so bad but I have never like red/burgundy in my hair. Maybe I will give it a try one of these days.
Posted by: Ladytee | January 28, 2009 at 07:38 PM
I am too for my middle daughter. I have heard so many good things and I think I have and understanding of what I need. Q
Posted by: Queeny | January 28, 2009 at 06:13 PM
I have purchased some henna, and will use it sometime after the hair challenge. I am going for that 'burgandy' tone. It really conditions your strands!
LHDC: Hi, Delilah! YES that is what I heard! Henna is supposed to be the BOMB! There is a whole LOT of info out there about it. What brand did you get?
Posted by: Delilah | January 27, 2009 at 01:26 PM
I've always wated to try that, i've never dyed my hair before at all. BUt if i did i would use henna.
Posted by: Tiffany@EbonyIntuition | January 27, 2009 at 04:59 AM