If you will go over to the Growing Tomatoes forum here and put AZ Arizona in the search bar there several discussions will come up from the AZ tomato growers there that will be of interest to you.

The same (and even more info on them) is also available on the Arizona Gardening forum here.

But from all my reading of their posts I 'think' March will be considered a late planting date. Not so much because the plants won't survive - they will if kept well watered - but because they won't set fruit (Blossom Drop) because of the air temps.

Of course this varies depending on exactly where you are in AZ but the AZ forum has folks from all over the state. Eg. planting times differ for the Flagstaff area from the Phoenix area where fall gardening seems to work best.

Unfortunately peppers also suffer from Blossom Drop (see FAQ here on it) but not quite as badly as tomatoes do. Sweet Potatoes, given good loose soil and tons of water and nutrients should do fine IMO.

Hope this helps.

Dave

Here is a link that might be useful: AZ Gardening forum