How does harvesting a plant at different times of the day (e.g., jasmine flowers in the early morning) affect the yield and aromatic quality of the essential oil?

The Impact of Harvesting Time on Essential Oil Yield and Aroma

Hey, I'm really into studying essential oils and have even tried extracting some simple plant oils from my own garden, so I'll share my experience. Simply put, harvesting plants at different times does affect essential oil yield and aroma quality, mainly because a plant's "biological clock" causes it to produce and release aromatic compounds differently throughout the day. Let's take jasmine—mentioned in the question—as an example, while also discussing general principles.

Why Harvesting Time Matters

The amount of essential oils (those fragrant volatile compounds) in plants isn't constant. They're influenced by light, temperature, humidity, and even the plant's own metabolic rhythm. For example:

Early morning harvest (e.g., jasmine around sunrise): Cool temperatures and dew mean oils haven’t evaporated under the sun yet. Yield is often higher because oils accumulated overnight remain intact. The aroma is purer and fresher, without interference from heat-induced off-notes.
Midday or afternoon harvest: High sun and rising temperatures cause partial evaporation of oils, reducing yield. The scent may be stronger but uneven, with some compounds degrading, resulting in a less refined aroma.
Evening or dusk harvest: Some plants (like night-blooming jasmine or certain flowers) release peak fragrance at night. But for non-nocturnal plants, oil content may be low.

Specifically for jasmine, based on research and my own trials: early morning is golden hour! Jasmine buds open at night, with aromatic compounds (like phenylethanol and jasmone) peaking at dawn. Harvesting early locks in maximum oil, boosting yield by 20–30% (a rough figure I’ve seen in books). Aroma quality is also superior—softer, longer-lasting, without the astringency of afternoon-harvested oils.

Impact on Yield

Optimal timing usually increases yield: Roses or lavender, for instance, are also best harvested at dawn. After a night of "rest," plants hold the most oil. Midday heat causes oil loss, reducing extractable volume.
But it’s not absolute: Plants like mint may yield more when harvested in the afternoon, as sunlight stimulates oil production. It depends on the species.

Impact on Aroma Quality

Compound ratios shift: Essential oils contain hundreds of compounds; their proportions vary with harvest time. Dawn-harvested jasmine smells floral and sweet; afternoon-harvested oil may be grassier or sharper.
Overall quality: Early-harvested oils are often more stable, less prone to oxidation, and retain aroma longer during storage. Late harvests, if timed with plant "fatigue," yield weaker scents.

My advice: If you harvest plants for oils, research the optimal time for that species or experiment with small batches. For example, next time you pick jasmine, split it into dawn and midday harvests, extract, then compare—the difference is quite noticeable! This hands-on approach makes the impact clear. In short, timing it right boosts both quantity and elevates quality.