Pardon my ignorance, as I just now heard of the X10, but can one plug these kind of sensors into it?
No, at least not directly.
The sensors you reference have a serial data output which can provide analog data (changing temp, humidity, etc.) to the serial I/O of a computer. You probably need special software.
Technically any sensor that provides a contact closure can be interfaced to X10 through the X10 "Power Flash module (Also known as "Burglar Alarm Interface" module). The X10 CM15A and ActiveHome Pro software is the X10 computer interface for home automation.
If you are a programmer, it might be possible to interface the Growtronics sensors to X10's AHP via the AHP Software Development Kit.
That said; you might be able to find other sensor systems which could provide a contact closure interface to the Power Flash.
Heed Pucks words. X10 transmits control codes over the homes power lines, which makes the signal susceptible to power line noise and coupling problems. Meaning: you can not count on the signal always getting to its target.