Not sure what exactly you are asking, but silicons work like this:
- If they are below their planetary population cap, they grow at a steady rate
- diffrently from aquatic and carbon life, they can't accelerate that rate buy planetary improvements (was that your question?)
- if you hit the popcap, you need durantium, to build a city in order to raise the popcap
There are fun exceptions to this, like using the slaver ability, so you can also build work camps to increase your popcap.
If you want a higher growth rate, you can get the prolific ability an/or the growth trait.
Morale also helps a bit (up to 25%)
