Where our data comes from
Every number has a source.
We built Siltwell's plant catalog by hand from public horticultural references. We did not scrape it or license it from a third-party database. A person chose and typed in every value, which keeps the catalog small enough to review in full. It also keeps out the silent errors that a bulk import of unvetted data brings in. Here's where each number comes from.
The plant catalog
The 150+ entries in Siltwell's catalog draw on these public horticultural references:
- University extension guides (Cornell, Oregon State, University of Minnesota, RHS Grow Your Own) for in-row spacing, days-to-maturity, and minimum soil temperatures.
- Square-Foot Gardening convention (Mel Bartholomew's 1, 4, 9, and 16 plants-per-square tiers) for planting density.
- RHS and standard botanical taxonomy for mapping each species to its family, then to a crop-rotation bucket.
- Seed-catalog norms (Johnny's Selected Seeds, Baker Creek) for days-to-maturity on crops that extension guides cover sparsely.
Frost dates
Your first- and last-frost estimates come from ten years of local weather history for your location. A hardiness zone is set by the average coldest night of the year, so it can't tell you when frost starts in fall or ends in spring. We estimate those dates from the daily lows at your location.
Harvest value (calories and dollars)
The "you grew about $X, N kcal" harvest summary uses USDA FoodData Central for calories per 100 g, and USDA-ERS retail price data (2025–2026 US grocery averages) for dollar value. It's a deliberate estimate, and the app marks it with "≈". Store prices drift with season and region, so use the dollar figure as motivation. It is too rough for bookkeeping.
Weather and your station
Forecasts and historical weather come from Open-Meteo. The free microclimate checker reads nearby home weather stations through a commercial feed. On Pro, you can connect your own Ecowitt, Ambient Weather, Davis, or Tempest station. Per-bed soil readings need an Ecowitt, Ambient, or Davis sensor. A Tempest has none, so add an Ecowitt gateway with WH51 probes. We use your keys only to read your data, and we don't sell it.
Why hand-curated?
A person can read a small, cited catalog end to end in an afternoon. No third-party license restricts it. The whole catalog sits in one readable file. A hundred-thousand-row import can hide silent errors that no one ever reads. When one of our values is wrong, the fix is one line.