Like the swiss-army knife of cleaning, castile soap has more household and personal care uses than we can count. (It makes a great DIY laundry soap, natural bathroom cleaner, and bubble bath, just to start.)
If you're any combination of thrifty, crafty, or crunchy, you will appreciate that castile soap is (among about a million other things) cheap, versatile, and biodegradable—which means it's both safe and easy to use on many surfaces, fabrics, and even your body.
But keep in mind that just because something is "natural" doesn't mean it's effective (or safe) to use on everything under the sun. Curious how to put that bottle of Dr. Bronner's to use in your home? Start with how not to use it:
Don't mix it directly with acids like vinegar or lemon
Remember learning about acids and bases in high school science? While acids (like vinegar) and bases (like castile soap) are powerful cleaning tools on their own, Lisa Bronner—Dr. Bronner's granddaughter—cautions mixing castile with any acidic ingredients. Rather than doing double duty cleaning a given surface, a mixture of castile soap and vinegar or lemon will accomplish the opposite, resulting in a white, curdled solution that will likely leave a yucky film behind on your counter.
Don't clean hard surfaces without using an acid afterward
Back to acids. Castile soap is a reliable and thorough cleaner, but on shiny or hard surfaces, it can leave a deposit of salt film behind. Even though you want to avoid mixing castile soap with acids, vinegar or lemon are great tools for cutting the leftover salt deposit. For castile-washed dishes, Lisa Bronner recommends dipping them in a vinegar-water solution of 1 cup vinegar per quart of water. You could use a similar solution to rinse filmy countertops.
Don't use with hard water (unless you want a little extra work)
Given its high mineral content, using castile soap (remember the salt deposits?) with hard water can result in some extra soap scum or residue. While your surfaces are probably still clean, mixing hard water and castile soap means you'll probably have to use the vinegar solution every time.
Don't use it on your hair without conditioner
If you're into the "no poo" method, castile soap is a great option for a squeaky-clean scalp — try pre-mixing a tablespoon of liquid castile with a cup of water. But, as the Dr. Bronner's website notes, the soap can also leave your hair tangled and matted. The best solution for silky, soft hair? Dr. Bronner recommends following up with an acidic conditioning rinse, like apple cider vinegar or their lemon juice formula.
Don't wash color-treated hair with it
Like baking soda, castile soap—even though it's chemical-free—can be harsh on dyed or highlighted hair, stripping follicles of color. To protect your colored hair, it's probably best to stick with a color-safe shampoo.
Don't use too much on plants
Castile soap can be a powerful insecticide, but it's important not to overdo it on your plants. Since it can remove a plant's natural protective, waxy coating, spraying too much castile soap directly on your plants could leave them more susceptible to pathogens, or even burn them. If you find your plants are damaged after spraying with your DIY insecticide, simply cut the amount of castile soap in your solution in half.