Why does it say "[ba'Boker] Yatzitz v'Chalaf"?
Rashi: Immediately after it sprouts, it passes (withers).
Radak: "V'Chalaf" is like "Im Yikares v'Od Yachalif" (Iyov 14:7), "Yachalifu Ko'ach" (Yeshayah 40:31) - renewal. If in the morning (youth) one was serene, at night (old age) it will dry. If grass is moist in the morning, when the sun is not so strong, at evening, after the sun beat on it the entire day, it is cut off and dries. Yemolel is a four-letter root.
Malbim: In the present morning, that grass sprouts and enters existence, also that grass will be cut off and dry at night. Also the current existence does not last; it is like a flower that sprouts, lasts one day, and is cut off and dry at night.
What is the meaning of "la'Erev Yemolel v'Yavesh"?
Refer to 90:6:1:2-3.