How the grow advisor works

When you simulate a cross, a 'Get growing recommendations' button appears under the result. It produces a full grow plan — light, temperature, humidity, watering and feeding, height and training, season and harvest timing, an indoor kit list, and what to watch out for. This article explains exactly how that plan is built and where its numbers come from.

It's rules, not a chatbot

The advisor does NOT call a large language model to write the advice. It's a deterministic function: it reads the predicted plant's traits and applies a fixed set of horticultural rules. That's a deliberate choice — a rule can't hallucinate a number or invent a fake study. The same predicted plant always gives exactly the same plan, and every quantitative claim is tagged to a real, named reference you can look up (listed at the bottom of the plan and again below).

The trade-off is that the writing is templated rather than free-flowing. We think that's the right call for grow advice, where a confidently-worded wrong number can cost you a whole crop. An optional AI layer could later rephrase this same rule-checked content into friendlier prose without changing any of the facts — the rules would stay the source of truth.

What it reads from the predicted plant

• Indica/sativa lean (indica %) → growth habit, expected height, how much it stretches, and how long it flowers.
• Flowering days (and its low–high range) → indoor schedule and the outdoor harvest window.
• Yield score and bud density → how hard to push the light, and how much to worry about bud rot.
• CBD level and chemotype mix → a heads-up when the flower will feel milder than a pure-THC strain.
• Stability score → whether to grow several seeds and select, because the plants will vary.

The rules, and the science behind them

Light. Cannabis is a short-day plant — it grows leaves under long days and starts flowering when nights get long enough (the 18/6 → 12/12 switch). Indoors, flower yield rises roughly in step with how bright the canopy is, so the advisor points you at a strong flowering light level and pushes the brighter end for high-yield crosses. (Potter 2014; Rodriguez-Morrison et al. 2021; Backer et al. 2019.)

Temperature and humidity. Photosynthesis is fastest around 25–30 °C and falls off in the cold or extreme heat, so the plan targets warm-but-not-hot days and a cooler flowering room. Humidity steps down as the plant flowers, because dense buds plus damp, still air are exactly what bud rot needs — so denser, indica-leaning or high-yield crosses get a stronger airflow-and-low-humidity warning. (Chandra et al. 2008; Punja 2021.)

Feeding. The plant wants more nitrogen while building leaves and a different, lower flowering feed once buds set; over-feeding hurts more than under-feeding. The advice to ramp nutrients up slowly comes straight from that. (Caplan et al. 2017.)

Height and training. Sativa-leaning plants stretch more and finish later, so the height estimate and the 'give it headroom / train early' notes scale with the indica/sativa lean. Topping and tying the plant down to spread the canopy is recommended because manipulating the plant's architecture makes yield and potency more even across it. (Danziger & Bernstein 2021.)

Timing. Indoors you set the photoperiod clock yourself. Outdoors in the northern hemisphere, flowering generally begins as nights lengthen in late summer; the advisor adds the cross's flowering days to an early-September onset to estimate a harvest window, and tells you to confirm by the trichomes rather than the date.

What it deliberately won't do

• It won't give exact wattages or yields for your specific room — those depend on your tent size, light, and skill, which it can't see. Numbers are typical ranges, flagged as such.
• It makes no medical claims and won't tell you how to consume anything.
• It assumes you're growing legally. Cannabis cultivation is illegal in many places — the advisor says so and that's on you to check.
• The height figure is genotype-typical for an untrained plant; pot size and training change it dramatically.

Sources

• Chandra, Lata, Khan & ElSohly (2008), Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO₂, Physiology and Molecular Biology of Plants 14:299–306.
• Rodriguez-Morrison, Llewellyn & Zheng (2021), Cannabis Yield Increased Proportionally With Light Intensity…, Frontiers in Plant Science 12:725078.
• Backer et al. (2019), Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Affecting Cannabis Yield, Frontiers in Plant Science 10:495.
• Potter (2014), A review of the cultivation and processing of cannabis for prescription medicines in the UK, Drug Testing and Analysis 6:31–38.
• Caplan, Dixon & Zheng (2017), Optimal Rate of Organic Fertilizer during the Vegetative- and Flowering-stages for Cannabis…, HortScience 52(9).
• Danziger & Bernstein (2021), Plant architecture manipulation increases cannabinoid standardization in drug-type medical cannabis, Industrial Crops and Products 167:113528.
• Punja (2021), Emerging diseases of Cannabis sativa and sustainable management, Pest Management Science 77:3857–3870.