I am also starting to try in March and have been taking folic acid since the start of Jan (which was when we started to discuss trying to conceive, we were originally going to start trying in May but have since decided to put it forward as far as we can, hence now March)
You should start taking it now along with vit d. you could take some trying to conceive tablets but that's up to you, the only things you need to take are the folic acid and the vit d.
Bring on March