My brother in law and his wife are really into "green" things and are somewhat hippies. Im planning on getting them a grow your own herbs and spices kit but i need another idea as well.
A great thing to match the herbs would be some nice 'terra cotta' flower pots, if they are not already included in the kit you bought. Terra cotta flower pots are made of natural clay (eco friendly), and you can get some really pretty engraved (or plain) ones for a very affordable price. These kinds of pots are often suggested for herbs.
Another idea you could try is getting wine glasses made from recycled glass. You can make your sister in law a basket with a bunch of natural pampering lotions, oils, salts, etc, too. If you really want to support their green ideas, you could also go and make a donation to an environmental charity or cause in their names.
Last, but not least, you could wrap your gifts in wrapping paper that's 100% recycled.
a home made present.. prob wrapped in recycled paper or newspaper... make something like like jam, or perserves, or those jars that have the premixed soups in them..
or make some candles out of beeswax or soy and wrap it up or even make your own soap..
enviro friendly people love homemade gifts! the herb garden is an excellent idea as well
one of those upside down strawberry/tomato planters. also if its for an anniverysary i would make a mini-scrapbook for them with 100% recycled materials.
mayb buy them a chia pet or something like that