Frühling vs. lenz
While both German words Frühling and Lenz translate to the season of spring, they are not interchangeable. Their difference lies entirely in their style and frequency of use, with one being the standard modern term and the other being an archaic, poetic alternative.
Frühling
A1This is the standard, common, and universally used word for spring. You will hear and see Frühling in everyday conversation, weather forecasts, news reports, and modern writing. It is the default word for the season.
Im Frühling werden die Tage wieder länger und wärmer.
(In spring, the days get longer and warmer again.)
Der Frühling ist definitiv meine Lieblingsjahreszeit.
(Spring is definitely my favorite season.)
Die ersten Frühlingsblumen kann man schon im Park sehen.
(You can already see the first spring flowers in the park.)
Wir planen unseren Urlaub für den nächsten Frühling.
(We are planning our vacation for next spring.)
Lenz
C1This is an outdated, poetic, and literary word for spring. Using Lenz in a normal conversation today would sound very unusual, old-fashioned, or even pretentious. It is reserved for poetry, classical songs, literature, and occasionally for evoking a romantic or nostalgic atmosphere.
Nun will der Lenz uns grüßen, von Ferne klingt Gesang.
(Now spring wants to greet us, from afar singing can be heard.)
Der Dichter beschrieb, wie der holde Lenz die Natur erweckt.
(The poet described how the fair spring awakens nature.)
In alten Volksliedern wird oft vom Lenz gesungen.
(Old folk songs often sing of spring.)
Sie erlebte gerade den Lenz ihres Lebens.
(She was currently experiencing the spring of her life.)
Wenn der Lenz ins Land zieht, blühen alle Herzen auf.
(When spring moves into the country, all hearts blossom.)
Summary
In short, always use Frühling for spring in any normal, modern context. Reserve Lenz for when you are discussing poetry, quoting old songs, or deliberately trying to sound artistic or old-fashioned. Frühling is for everyday use; Lenz is for literary effect.