Learn Spanish (Latin America): Las flores son bonitas en la primavera.

In Spanish, you generally use a definite article (el or la) before the names of the seasons. While you might sometimes hear en primavera, using en la primavera is very common and completely natural when talking about what happens during that time of year.

Is flor feminine even though it does not end in -a?

Yes! While many feminine words end in -a, flor (flower) is an exception. Because it is feminine, it uses la in the singular and las in the plural. And since it ends in a consonant, you add -es to make the plural flores.

Why use son instead of están for how the flowers look?

We use son (from the verb ser) because this sentence describes a general characteristic or fact about flowers during the spring. We use estar for temporary conditions, so if we said están bonitas, it would mean some specific flowers look pretty right at this exact moment.

Why does the word bonitas end in -as?