i had a coleus like yours for 2 years but i put it into bigger pots too fast, never did get dense nor sufficient sunlight.
this is my current set. got a few pics to post
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i purchased 8 celosia a year ago, didnt think ahead to find proper places for them so most went into pots. they got top healvy and keeled over. never purchased any again and i dont think i'll have to. the first celosia pic is regrowth from seeds. the were 2 transplanted last year and they died in there, didnt remove them so they dropped the seeds. had put some of that same soil into other pots and removed the sprouts unsuspectingly until the 2nd celosia pic to see just what the sprouts were. gald i did so.
the coleus was a 4 inch pot (canadian tire purchase) with 3 plants. been lazy so far to change its current 6 inch pot
take a look at thesmall yellow triangular section, never had a live one like that ever with my celosia. must be a recessive gene for this particular individual plant. its only been in 1/20 celosia ive owned. i know the large pot is over crowded (11 plants) but i'll transfer some over to the smaller pots.
my favorite is the newest purchase, its atleast 2 months old. purchased the bag of seeds and grew it, had another that i gave to a friend and the 5 other sprouts didnt last long. its just above 1.5ft talland nearly 2 inches wide on the flower. its just letting out the last 3 petal on the top of the flower.