The most common and most likely answer to this crossword clue is the 6 letter word CAMBIA
C
A
M
B
I
A
Buddy explains!
The straight part
We know that "What’ll determine root growth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what’ll determine root growth = cambia.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CAMBIA mean?
CAMBIA noun- A layer of cells between the xylem and the phloem that is responsible for the secondary growth of roots and stems.
- Periosteum, a membrane that covers the outer surface of bones
- One of the humours formerly believed to nourish the bodily organs.