成長 and 成熟: growth and a state of maturity
Compare growth in a seedling or person with ripening fruit or a maturing plan, following the targets and changes stated in the examples.
Growth as a change with 成長
成長 (せいちょう) refers to growth or development. The example 「苗木の成長を毎月写真に記録した。」 is translated as “I photographed the seedling's growth every month.” The seedling's growth is photographed every month. The recording interval is stated, but no amount of growth is supplied.
The example 「失敗を乗り越えた経験が彼を成長させた。」 is translated as “Overcoming failure helped him grow.” The experience of overcoming failure helps a person grow. 成長 here goes beyond an increase in physical height or size.
Maturity with 成熟
成熟 (せいじゅく) refers to maturity or ripening. The example 「果実が成熟するまで収穫を待つ。」 is translated as “We wait to harvest the fruit until it ripens.” 成熟するまで connects waiting to harvest with the fruit's ripening. It does not report that ripening or harvesting is already complete.
The example 「議論を重ねるうちに計画が成熟してきた。」 is translated as “The plan matured through repeated discussion.” The plan has matured through repeated discussion. 成熟 can describe an abstract plan as well as ripening fruit.
Identify the target and emphasis of the change
成長 describes a seedling's growth or a person's growth through experience. 成熟 describes ripening fruit or a maturing plan. Growth is not limited to size, and maturity is not limited to a person's mental state.
Photographs of the seedling and the experience of overcoming failure show the target or occasion of growth. Separate waiting for ripening from the plan's stated maturation, without making growth lead inevitably to completed maturity.
What changes are described when overcoming failure makes a person 成長 and repeated discussion makes a plan 成熟?
Show the answer and why
The first describes personal growth through experience; the second describes a plan becoming mature through discussion. Do not restrict 成長 to size or 成熟 to a person's mental state, and keep waiting for fruit to ripen separate from completed ripening.