Too thin and weak to help in the garden? (5)
I believe the answer is:
weedy
'too thin' is the definition.
'weedy' can be an answer for 'thin' (similar in meaning). I am not certain of the 'too' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for weedy that I've seen before include "Scraggy" , "like an untended flower bed?" , "scrawny" , "Thin, puny (colloq.)" , "quite unlike Charles Atlas" .)