You can use the water from an aquarium if you have one. If not, an all natural fish emulsion works well. I pick mine up at my local hardware store or nursery.

your plants would love some worm castings or compost.

Try watering them with the water leftover from steaming vegetables or boiling pasta (unsalted, of course).

More basic, Miracle Grow. Maybe not "green" but they have measurements for indoor plants, and the plants love it.

I haven't tried it yet, but Epsom salts are supposed to be good for some plants, as are dried coffee grounds.

Put all your food scraps in a pile in the yard and when it turns to dirt you put it on your houseplants.

I pour the leftover green tea from a pot of tea and coffee grounds into my work plants. They are crazy happy.

I use dried coffee ground too and I like to think it works.

I saw some Osmocote in the organic section of my local nursery. I'd go that route for general purpose.

You can also use compost, but you need to let it sit out for a while before using it on indoor plants.

Epsom salt works best for plants that like magnesium. I use my aquarium water on my plants also, but I wouldn't use fish emulsion indoors as it smells to high heaven!