Posted: 13/04/2012 at 08:53
pierox, Amy's post (above) is a good starting point. The plants are limp and vine-like? What colour are the leaves and stems? How much sunlight are they getting? Ample, or even tons of sunlight, won't cause them to be limp. Insufficient sunlight could well have them straining for light.
Another possibility. Excessive fertilising, particularly with a nitrogen-rich fertiliser, can cause excessive growth. How often do you fertilise and what with?
Genuine determinate varieties won't grow as you describe because they're genetically incapable of it. If you want more contained plants, determinates are the way to go.
It sounds like you have indeterminates. You can always remove the growing tips of an indeterminate variety when it reaches a size that satisfies you.