These are typically seed dahlias (grown from seed rather than a mature tuber) and tend to stay quite compact their first season at least. If you harvest and store the tubers that form over winter for planting out next season. I'd plan on them getting larger......maybe as much as double this year. Most of these are smaller, dwarf or more compact forms to begin with so unlikely to produce the big 6'+ tall plants like the dinner plate dahlias.

thanks for the information.