What to send
A sunflower is the obvious choice and the right one — bright, unmistakable, and it photographs well in every family group shot. Pair it with a daisy if you want it lighter, or a carnation if you want it to feel more grown-up.
If the graduation is for someone older, returning to study, skip the bright yellow. A peony with a camellia reads as congratulations without the school-leaver energy.
What to write
The degree is the least interesting thing to congratulate. Everyone will say well done; almost nobody will mention what the last three years actually cost.
Name the part you watched: the evening classes after full shifts, the February where they nearly stopped, the essays written in a kitchen at midnight. “You kept going in February” lands harder than any mention of the result.
If you cannot be there
Say that you wish you were there, once, and then let the rest of the note be about them. The bouquet arrives on their phone during a long day of standing in a gown, which is exactly when a message lands best.