The gardeners paint the roses red to avoid the Queen of Hearts’ anger.
Alice discovers three playing-card gardeners painting white rose bushes red in the Queen’s garden. They explain that they accidentally planted white roses, even though the Queen wanted red ones. Since the Queen is notorious for ordering people’s heads chopped off, the gardeners try to conceal their mistake before she notices.
The episode introduces the Queen’s volatile temper just before Alice meets her and joins the croquet game. The gardeners’ disguise does not work: the Queen sees the white roses and immediately becomes furious, ordering punishment. Alice helps hide the gardeners in a flowerpot, temporarily preventing their execution. The scene is often remembered from the 1951 Disney film, which also shows card soldiers painting the roses and emphasizes the Queen’s command, “Off with their heads!”
A common mix-up is to say the gardeners paint red roses white. In Carroll’s story, the original roses are white and the gardeners paint them red because the Queen dislikes white roses.