Greenhouse Planters-insulate? Depth?

I am building some raised planters today for my greenhouse. I was wondering if there would be a benefit to insulating the sides of the planters with foam insulation? Just thinking it might help to retain heat in the containers?

What would be a good depth for planters?

Foam over a wood frame? I doubt it. Wood insulates, but I suspect most heat would go straight up.

I was actually thinking of lining the planters with foam-thought there might be two fold benefit-insulation and also protect the wood sides from moisture.

Ok. Foam inside wood. Description was vague. I would think water would wick into wood unless all edges contacting dirt was sealed.if bottom still has contact, not sure proofing the sides will help