How we rate
Every verdict on this site traces to a growing database, a documented compatibility rule, and a documented cost model. This page is the documentation.
The GrowScore
GrowScore is a 0–100 editorial score across five weighted axes, applied identically to all 8 systems in the database:
- Versatility25%
- How much of the plant database the system can actually grow — clearance, pod count, and light coverage decide the compatibility column, and the compatibility column decides this axis.
- Reliability of design20%
- Pumps, sensors, and light timers that keep working; designs that degrade gracefully when the app, the cloud, or your attention lapses.
- Cost honesty25%
- How close the sticker is to what you actually spend. Pricey proprietary pods, membership-gated features, and plan-dependent economics all cost points here — transparency earns them back.
- Openness15%
- Can you use generic pods, your own seeds, third-party nutrients? Open ecosystems score higher because they cap your running costs forever.
- Value15%
- Capability per dollar — judged against price plus realistic running cost, never the sticker alone.
The compatibility rule
Every cell in the 8×12 matrix is computed from two inputs, with no per-cell editorial override:
- Height margin — the system's usable light clearance minus the plant's mature height need. A negative margin is an automatic skip: the plant grows into the light.
- Pod difficulty — easy crops (greens, most herbs) thrive with ~2 inches of margin; moderate crops (fruiting and slow-start plants) need ~6 inches of margin to thrive and rate with-care below it; hard crops (pollination-and-patience plants like strawberries) never rate better than with-care, and need real headroom even for that.
Plant facts — height needs, harvest windows, pollination, cut-and-come-again behavior — are standard gardening knowledge, stated conservatively. We don't invent yields and we don't promise harvest dates.
The running-cost model
Two lines, computed identically for every system:
- Electricity = light wattage class × 16 h/day × 30 days ÷ 1000 × $0.17/kWh. The rate is a typical US residential assumption — it's labeled everywhere it appears and editable in the calculator. Wattages are approximate class figures; actual draw varies with light mode.
- Pods = pods in use × typical per-pod price ÷ a ~2-month grow cycle. Open systems that take generic seeds get pennies-per-pod figures; proprietary ecosystems get their typical street price; membership-centric systems are flagged because plan economics replace pod math — we say so rather than guessing plan prices that change.
Where the numbers come from
Manufacturer published specs and refill pricing, checked against major-retailer street prices. Prices are typical street-price figures, not live quotes; availability and plan structures shift, and we frame those claims durably ("check current plans") instead of pretending they're fixed. Spot a stale number? Tell us — a correction recomputes every verdict, ranking, and cell site-wide.
Commissions and the firewall
GrowPodHQ earns affiliate commissions — including from Amazon — when you buy through our links. Scores, compatibility verdicts, and cost estimates are computed from the database before any link is attached; no brand sees, sponsors, or edits a rating. A system with expensive proprietary pods keeps its cost-honesty penalty no matter how well its links convert.
Corrections
Pricing and spec corrections get priority over everything else — the database is the product. Contact us.