At which point does growing plants require quintessence

In Mage the Ascension 20th Anniversary edition you need quintessence to create things from nothing. With the life sphere 3 dots (+ prime 2 dots) you can create simple life (including plants) with a point of quintessence (page 516-517 in Mage the Ascension 20th Anniversary Edition core rulebook).

With 2 dots the page 516 states:
Although he can’t yet transmute them into other states of being, he can cause flowers to bloom or wither, help trees bear fruit, and so on.
"Help a tree bear fruit" seems to imply that some limited growth also works without spending quintessence.

In the case of simple lifeforms like moss or funghi them blooming would just mean that there is more of it there afterwards since those plants mostly only grow larger.

My question is, at which point of growth would you have to use quintessence to make the plant grow larger if you use a Life 2 dot spell to bloom a patch of moss for example.

Is there precedent for this in a rulebook or is it just based on storyteller discretion?