
Keep trying. You can grow them pretty much as high as you want. Here's an example of me breeding the short little starting plants into a taller and taller version (there are many skipped generation in this picture). Pay attention to the number and size of the segments in the stem. Those can both change and impact the height of a plant. Children will be different from their parent in somewhat randomized ways, so not every child will be taller. You just need to keep an eye out for the ones that are.