Guardian 23992

[Aperio]

Turned up one end in bud (8)? "Unopened " is an anagram of "up one end" and this fits the check letters.
However, surely bud means the opposite: opened or at least partly opened?

[eddiebun]

As a noun a bud is an unopened flower

[Ont-ice]

1. Botany
a. A small protuberance on a stem or branch, sometimes enclosed in protective scales and containing an undeveloped shoot, leaf, or flower.

[ulysses100]

When a bud opens it is called a budburst -- and is one of the features recorded by phenologists
Look at www.naturescalendar.org.uk and swell the number of recorders..