Question
hi im attempting my first terranium with moss i got from around the house i was wandering is it possible to use just rocks and water or do i have to have soil? also is there any safe homemade pesticide i could use on it? do you know how fast it grows? thank you for your time

Answer
This is one of those questions that I start by saying it will be a trial and error process to see what works. I say this because there are several kinds of moss. The fact that your moss comes from your outdoor yard and you are putting it into an enclosed terrarium environment will be the first challenge. It makes a difference if the terrarium is closed or open and how big it is. I have used a basic round fish bowl. I put a cup of pebbles in the bottom and 2 cups of 3/4 potting soil and 1/4 peat moss mixed and placed on top of the pebbles. Place the moss on top of the soil and press it into the soil to make good contact. With a clean spray bottle, spray to moisten the moss and soil. If the container is open, spray every day, or as needed. Do not over water. If you smell a bad odor coming from the moss, it is rotting from too much water.
Yes it is possible to grow moss on rocks, but it is harder to get the moisture ratio right. With stone, the water runs off, where with soil the water holds to the roots. I have never used a pesticide on moss. If manual smashing of the bugs is not possible then apply a light "SAFER SOAP" for houseplants. Read the directions. It is all "natural".
Moss grows at varying rates depending on the kind of moss and the environment so that is difficult to predict. But in general it is not a fast growing plant.
It can be fun to create a scene with the moss with a nice stone, and a path, and a small cottage.
DO NOT LET SUN BURN THE MOSS. Sun heat is the worst thing, but good light will make it grow much healthier.