there are two kind of roots: thick is called anchor root for water, thin one is for nutrition and water. you probably notice the thin root are spread over the top layer of soil. overtime the thin root will go down, because it has no way to go. you should not find any or much thinker root if growing them in can. just an observation.

謝謝toca9b的觀察與提醒
幾年來一直更換盆器與介質
從不計尺寸和深淺,有盆就好,介質亂調
到去年綜合幾位花友的意見,找到目前看來很滿意的方式~
小空間種花不易,量與質之間不得已的最大平衡
深盆~介質更要重排水透氣^^