Answer:
No
Step-by-step explanation:
Horizontal stem as a form of vegetative propagation does not persist in several plants. The stems run horizontally beneath the ground and give off above ground shoots with a corresponding below ground roots at intervals. The give-offs are capable of becoming independent organisms even after the horizontal stem has degraded which is sometimes the case with some plants.
Hence, the gardener's conclusion is incorrect because the horizontal stem might be a temporary one that degrades with time, leaving the off-shoots as independent plants.