How paints coats of primer is needed to paint wood trim?

Do you need to cover it very well, or will just one coat suffice? The trim is old wood, with the grain and everything.How paints coats of primer is needed to paint wood trim?
When I'm doing older wood like that, I usually use 2 coats of primer. I use a good stain blocking, self leveling primer which will give you a good base for your top coat. The primer I use is Zinser Bullseye 123.How paints coats of primer is needed to paint wood trim?
You should only need one coat of primer, and a stain-blocking primer is a good idea. The 2 and 3 coats comes in with your finish paint.
If the wood was stained in the past...use a primer with stain blocker. Even then it may take 2 or even 3 coats depending on how stained the old trim is.