二年生植物是指在两年期内完成其生命周期的部份显花植物。通常首年会完成发芽、长出根、茎及叶的生长阶段，并在寒冷季节进入休眠状态。这段时期的茎非常短、叶紧贴地面，呈矮丛型。在寒冬及春化现象后于翌年进入生长生殖阶段，这段时期植物的茎部会快速地变得长而细，出现抽苔现象。开花、结果并散播种子均在一年内完成，直至死亡。现时已知是二年生植物的数目远少于多年生植物及一年生植物。

在极端的气候环境下，二年生植物可能会于很短时间（例如仅得三到四个月）完成其生命周期。这种情况常见于在它们未有经历一年时间的生长阶段后，直接因寒冷天气及春化现象而被催生出开花结果。这种现象使不少人误以为这些二年生品种不过是一种一年生的植物。除了春化作用外，也有人透过加入植物激素，如赤霉素等以达致开花结果，不过在商业应用上并不常见。某些多年生植物在恶劣环境下，生命周期变短，也有被误以为二年生的植物。不过二年生植物一生中只会开一次花结一次果，而多年生植物则会每年开花结果。

A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots (vegetative structures), then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming a rosette. Many biennials require a cold treatment, or vernalization, before they will flower. During the next spring or summer, the stem of the biennial plant elongates greatly, or "bolts". This typically makes biennial vegetables such as spinach, fennel and lettuce unusable as food. The plant then flowers, producing fruits and seeds before it finally dies. There are far fewer biennials than either perennial plants or annual plants.