Lasting or remaining active throughout the year, or all the time.

(botany) A plant that is active throughout the year, or has a life cycle of more than two growing seasons. / A thing that lasts forever.

year after year (literally: each year) / constantly; with frequent recurrence

plural of perennial

(agriculture) The conversion of a plant from an annual to a perennial

The state of being perennial.

simple past tense and past participle of perennialize

present participle of perennialize

(botany, intransitive) To return year after year as a perennial. / (botany, transitive) To make perennial.

Third-person singular simple present indicative form of perennialize