The phrase "the first grown" is grammatically correct and usable in written English.
You could use it to refer to the first instance of something, such as "The first grown flowers of the season had a fragrant smell".
I know that I'm not the first grown up – or, more accurately, big kid – to write to you.
And she revealed in a recent interview, that the first grown up book she read, was Agatha Christie's The Mysterious Affair at Styles.
The Washington Post notes that while the latest blooms are "the first grown from start-to-finish in an official NASA mission," flowers have bloomed on the ISS before.
It became clear that irrigation is essential during establishment and the first growing season on all types of green roof and in all climates here considered.
This resulting biomat matures over the first growing season with operational parameters such as HRT further exerting a modest selective bias on community succession.
Successful species during the first growing season included Alyssum maritimum, Echium plantagineum 'Blue Bedder', Gypsophila muralis, Iberis amara, Iberis umbellata 'Fairy', Linaria elegans and Linaria maroccana.
Fifteen seedlings died during the first growing season in the field (assessment in the fall of 1999).
The fingerling period consisted of the first growing season from family size equalization to individual tagging.
Conflicting reports are available on the timing of floral commitment, ranging from the spring of the first growing season [ 4, 5, 9] or late summer of the first growing season [ 10], to the spring of the second growing season, immediately before flower differentiation [ 11].
The first means ensuring everyone has enough to eat; the second, growing it yourself.
The seconds grew – there was space in them – they grew as big as hospital buildings.
