Creatures Caves

To be honest, I always thought that plants and critters are some of the harder things to begin with. Organizing the lifecycle and balancing the reproduction can be a real hassle.

Anyways, the first 3 things your plant needs are
1) a working injection, e.g. by spraying seeds into a certain room
2) a main living script, ideally using the aforementioned timer script (script ID 9)
3) a simple remove script.

The creation script is the new: something plus the physical attributes like ACCG, AERO, PERM and so on and moving the object to a safe position. It typically goes at the very top of a cosfile. Make this work even if your plant does not even have any scripts to function properly yet. Make sure the plant goes where it is supposed to go and does no funny things, like flying off-screen or bouncing all over the place (unless you WANT that, of course).
This is also where you initialize variables you might need, such as a basic lifeforce or age counter.

The next step is making the removal script. It goes to the end of the cosfile and is introduced with RSCR. You want to run an enum # # # kill targ next for all classifiers/different agent types you used in order to remove them from the world and a scrx # # # # for each script you created, so the scripts no longer linger around. Since you are adding scripts later on, you may want to come back to your remove script from time to time to accommodate these changes.
It is extremely useful to have one early on, though, as the remove script will come in handy while testing, to get rid of pesky earlier prototypes.

The next is the timer script. This is where all the living happens. The nice thing is that it works very modular, so you can add stuff step by step. Once a thing works, you can easily move on to the next thing.
Start out with something simple, like growing every so often by changing the pose and stopping when fully grown.
From here you have a good position to tackle the more intricate parts of the script.

Then, when your basic plant is done, then you can think about adding extra actions like eating scripts for the seeds or emitting smells or something like that. These are all things that just "dangle" from the main lifecycle. It is the best to just slap them on top when you are done with the timer script.

Another tip I can give is this: make your plant age rather fast, maybe a step every 10-20 seconds or so. That way you can effectively test it without having to sit around forever. Once everything works as intended, you can slow down the whole thing to a reasonable speed simply by adjusting the TICK value.