I'm growing basil, cilantro, and mint on a countertop AeroGarden. The app says 16 hours but I've seen people run 18 hours. What's the sweet spot for herbs?

Q: I'm growing basil, cilantro, and mint on a countertop AeroGarden. The app says 16 hours but I've seen people run 18 hours. What's the sweet spot for herbs?

16 hours is the research-backed optimum for most culinary herbs. Running 18 hours yields marginally faster growth but increases electricity use and can trigger early bolting in cilantro. The correct answer also depends on which herb, since basil and mint tolerate long days differently than cilantro.

The 16-hour schedule in your AeroGarden app is well-calibrated for a mixed herb tray. Here's why, and where the nuance is.

Why 16 hours is the standard

Most culinary herbs are quantitatively long-day plants - meaning they grow vegetatively (producing leaves) under long light periods and shift toward flowering under shorter ones. 16 hours of light per day sits solidly in the vegetative zone for basil and mint, encouraging leaf production rather than flowering.

At 16 hours the daily light integral (DLI) - the total amount of photosynthetically active radiation delivered per day - is typically adequate for compact, productive countertop herb growth without exceeding what most kitchen-friendly LEDs handle efficiently.

Basil (16–18 hours, with a caveat)

Basil is a strong light consumer that genuinely benefits from up to 18 hours of light. More light = faster growth and larger leaves. The limitation at 18 hours is that basil starts signaling toward flowering faster; you'll want to pinch flower buds more aggressively. If leaf production is your priority and you're pinching regularly, 18 hours is fine for basil.

Mint (14–16 hours is plenty)

Mint is vigorous enough that it rarely needs more than 16 hours. Running 18 hours does increase growth rate but can make mint more prone to producing small, narrow leaves rather than the broad, aromatic leaves you want. Stick to 16 hours.

Cilantro (14 hours maximum)

This is the critical one. Cilantro is a long-day plant that bolts (flowers and sets seed) when day length exceeds 14–16 hours combined with temperatures above 70°F. In a warm kitchen with an 18-hour schedule, cilantro can begin bolting within 3–4 weeks rather than the typical 6–8 weeks. The leaves become bitter and sparse once bolting starts.

If you're running a mixed tray with cilantro, 16 hours is the compromise that keeps cilantro productive longer. If you drop cilantro from your tray, you have more flexibility to run 17–18 hours for your basil.

The electricity math

The difference between 16 and 18 hours on a typical AeroGarden Bounty (45W LED) is:

16 hours: 0.72 kWh/day = ~$0.094/day at $0.13/kWh = ~$34/year
18 hours: 0.81 kWh/day = ~$0.105/day = ~$38/year

The gap is small ($4/year), so electricity alone isn't a reason to choose either schedule.

Recommendation

Run 16 hours for a mixed basil/cilantro/mint tray. If you're growing only basil, 17–18 hours will accelerate growth noticeably. Always include a dark period of at least 6–8 hours - plants use this time for respiration and translocation of nutrients; 24-hour light causes stress in most herbs.

This answer is reviewed against published horticultural research. It is not a substitute for advice from a certified horticulturalist.