I have had my aquariums and indoor aquaponic mini systems for a while but for first couple of years I did not dare to get any plants. I bought some plants initially but they all died. After reading about different plants for aquarium and how to take care of them, I started off with java moss. This is one of the easiest plants to keep in your aquarium.
You can buy this at almost any aquarium related store. They are inexpensive as compared to many other plants. Java moss is very low maintenance plant which does not need a lot of light as well. I have seen this sold in stores between 5 and 10 dollars for a ball of moss little bigger then a ping pong ball.
The beauty of this particular plant is that it does not need a lot of work to maintain it. Since it is fast growing plant you can grow it and propagate to different aquariums as you see fit.
This plant does not have a visible root system and hence does not need any kind of soil. I have placed the Java Moss on river rocks, pebbles and logs in my aquariums. People use glue or string to attach the moss to the particular surface. I have tried both and also have tried to cover the moss on a rock with a net.
I have learned that you can get some from parks and even possibly from your own backyard. I saw some moss growing in my backyard couple of summers ago. I became curious and scraped some from there and washed it thoroughly under water. Then I placed it in a separate bottle filled with aquarium water. I monitored it for couple of weeks and was glad that it was thriving. Then I moved it to my aquarium where it is still thriving.