18" is great. No bottom is best. Bottoms cause drainage problems in many cases, water forms ponds, and roots rot. If you do use one make it an open wire mesh that will drain out the water quickly.

Dave

3x4x18" would be 18 cubic feet of soil so nine 2 cu ft bags or 18 1 cu ft ones!

You could probably do 10" or 12" depth and still be ok. No bottom though

Why be in such a hurry? Maybe just put these tomatoes in a container for this year and do some research?

Some things to think about.....how many beds? Do you have pests...gophers, rabbits, moles, etc? Do you need to amend your soil? How wide do you want your paths (I like 3' in order to maneuver a wheelbarrow), maybe get a truckload delivered or picked up by a friend with a truck, same with compost. Do you want to start a compost bin or system?

It would be great to read through these forums for the next year to get some real ideas!

I didn't find these forums until AFTER I made a whole bunch of mistakes! Nancy