Ok first for the astrolab you need 4 pieces then from the to floor of the severed hand go to Labelas Tower (left side entrance). You'll find that the entrance got destroyed... Go back and the Sheverash Tower (right side entrance). On level three of the tower you will find a passage to the left (instead of going up the stairs) take it and you'll emerge on a bridge that will lead you to Labelas Tower and to the astrolab lab.
Now for the gardener items.... these come much later in the game... in fact its a thing many ppl forget to do and it fetches a lot of experience (doing it and not forgetting to do it
)
The places are:
Pure water - Wyrm's Tooth (inside the dead dragon)
Seeds - Malavon's office in Lower Dorns Deep.
Birds and animals - buy from Nym in Svirfneblin Village Lower Dorns Deep.