Prior to replanting, the resemblance between all three arugula roquette plants (middle planter) was indisputable, as shown in the following image:
So, it was to my surprise that once in their own designated planters, each plant recuperated differently. As seen below, the one in the milk carton planter (covered with book pages for aesthetic purposes) grew tall and lanky; the arugula in the oatmeal container flourished all stout and wide with warm, forest-green growth; and lastly, the arugula in the can went to seed, both flowering and flower-like.
And yes, I did use good old organic soil for these planters, for I have learned my lesson. I've actually converted all my indoor plants to organic soil or a coco coir-organic soil mixture--except for my oregano plants, which currently reside in pure coir. The oregano may be replanted soon...
A hard-to-grow (for me, at least) shiso seedling is making its new home in the dark green planter that once housed the arugula. I am looking forward to sharing some photos soon.