First column, there's a 2 in the second row from below that already has two sunflowers. So the 3rd adjacent field must be empty.

The "4" clue forces the solution imho.

For everyone: Whenever you think you have to guess, use the hint feature.

In the more advanced levels you essentially have to "guess" then check whether the guess (e.g. using "pencil mode") leads to a valid solution or a conflict.