Why no-occasion flowers land harder
A birthday bouquet is expected. It proves you remembered a date. A Tuesday bouquet proves something different: that you were thinking about them when nothing required you to be.
That is why the note should not over-explain. “Was just thinking about you. That is the whole message” is a complete just-because note, and it is hard to improve on.
What to pick
Anything, honestly. Daisies if the person is bright. A peony if you want it to feel generous. A single camellia if the feeling is quiet.
The lowest-effort version that still works: one flower, one line, sent in under two minutes while you are thinking of them. The delay is what kills these gestures, not the choice of stem.
The habit, not the event
People who are good at this are not more romantic than everyone else. They just send the small thing at the moment they feel it, instead of saving it for a date that would justify it.
A link makes that possible because it costs nothing and takes less time than writing a text.