Several years ago I gave up all standardized hair products as a necessity. My hair was shoulder length, and besides a few trims I've let it grow since then. Through trial and error (and a lot of research) I've become familiar with most alternative techniques along with their pros and cons.
The first method I tried was soap with acid rinse. Quite literally a bar of plain lye soap used on my hair, rinse it out thoroughly, and then pour a mixture of vinegar and water over it all to finish it off. I never measured the vinegar, just got a pitcher of water and poured some in. I experimented with washing out the vinegar vs. letting it dry in, and determined that leaving it in worked best for me. I washed my hair every week or so with this method. It took about a month for my hair to get used to this process, during which time it looked and felt like cotton candy.
After that, it became fairly presentable, but I wasn't exactly happy with it.
Next I switched to the baking soda and vinegar method. Mix some baking soda with about a shampoo bottle's worth of water, pour through hair, rinse, and then apply vinegar rinse as before. Baking soda, I've found, is much easier than soap, because the harshness of the solution is very easily controlled: if you want to wash often, use a very diluted solution, if less often use a stronger solution. Also, there's no scrubbing the suds through your hair as with soap or shampoo; just pour it over your scalp and let it drain to the ends. My hair only improved switching to this method.Note: to avoid a chilly predicament, I recommend putting the desired amount of baking soda in an empty container, taking it with you to the shower, and then filling it up with hot shower water right before you plan to wash your hair. Cold water works best for acid rinses but is not a requirement.
Then I began experimenting with various herbs. You boil them into a "tea", strain, and apply, generally in the acid rinse. While some of them did make my hair a bit shinier or softer, I concluded that (for me) they generally are not worth the effort.
I have tried soapnuts, and concluded that they work about the same as diluted baking soda but require a lot more work (boiling, straining, and the resulting solution cannot be stored long because it goes bad). In theory, any plant material high in saponins should work, such as soapwort, snowberry, or even English Ivy. I've been meaning to experiment more with various plants just because I'd like to know my options, but haven't got around to it yet.
Oils can go a long way towards making product-free hair shiny and smooth. After a lot of experimentation I've found that jojoba oil works best (I know, it's actually a wax) and I sometimes use coconut oil instead. For about two months I once went without washing my hair at all (partly out of necessity, partly an experiment) and found that my thirsty hair needed an unorthodox amount of oil in that time to stay nice. However, to my surprise it never began to look oily. My conclusion was that so long as I had a good comb or two, this method of haircare would be satisfactory for me. I stopped only because it made my hair slippery, and the slipperiness in my updos was annoying me.
Many people with hair less thirsty than mine have found this no-water method works just fine without any additional oil. And no, your hair does not become smelly, but your scalp can get a little itchy from dead skin not being routinely removed, hence the need for a good comb.
Other methods are water only (just getting your hair wet) and vinegar rinse only. Lately water-only washing has been my method of choice for the ease and also for how well my updos stay when nothing slippery has been put in my hair. I should point out, this is my current method of choice even though I can now use hair conditioner again. Note: if anyone wants to try any alternative methods of hair care they should first wash with a clarifying shampoo and not use conditioner afterwards. The modern shampoo-conditioner method relies on 'cones (any ingredient ending in -cone) in the conditioner to coat the hair and then sulfates (in the shampoo) to strip the 'cones off before more are applied, as if refinishing a piece of wood furniture. Sulfates are the only things that can remove 'cones, and if you try a natural method without first removing them it won't work because nothing can affect the hair through the 'cone seal.