Growth Cycle — ruling 1

The size of the bonus is determined as Growth Cycle begins to resolve; it won’t change later in the turn if the number of Growth Cycles in your graveyard changes.

Growth Cycle — ruling 2

Because Growth Cycle is still on the stack as you perform its instructions, it isn’t in your graveyard and won’t add to the bonus the creature gets.

Growth Cycle : règles, fonctionnement et interactions (MTG)

Growth Cycle is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Target creature gets +3/+3 until end of turn. It gets an additional +2/+2 until end of turn for each card named Growth Cycle in your graveyard.

How it works : Growth Cycle

Original English text — Wizards of the Coast / Scryfall

#1July 12, 2019· Wizards of the Coast
The size of the bonus is determined as Growth Cycle begins to resolve; it won’t change later in the turn if the number of Growth Cycles in your graveyard changes.
No other card is named in this ruling.
#2July 12, 2019· Wizards of the Coast
Because Growth Cycle is still on the stack as you perform its instructions, it isn’t in your graveyard and won’t add to the bonus the creature gets.
No other card is named in this ruling.