That scene kinda reminds me of Alice in Wonderland where the Queen of Hearts' gardeners are "painting the roses red"...
Every time I've finished Return of the King, I've always found mysel wondering about the royal gardener assigned to the new White Tree...just sweatin' it out, terrified of root rot, etc, etc. So this was a fun little character arc to indulge in.
Everyone else in Gondor all happy 'n excited that Sauron's gone...and this one dude just FILLED with anxiety.
Actually (I know, this makes me one of the biggest nerds ever that I know this), Aragorn took care of the tree himself. It says that in the appendices that follow the end of ROTK.