Where every value comes from
Where each value comes from, what happens when two sources disagree, and what we do when a value cannot be sourced at all.
Last updated August 2026
extension, USDA and ASPCA
when a source is missing
when it was last checked
The source hierarchy
Every care value on this site can be traced to one of three tiers, and they are used in order.
The land-grant university extension services are where American horticultural guidance is actually produced and revised. They are regional, which matters, because a plant behaves differently in the humid southeast than on the dry side of the Cascades at the same rated zone.
Used for: watering, soil, spacing, pruning timing, propagation, pest treatment In practice: on the lavender entry, the watering interval of every two to three weeks until buds form is Colorado State Extension’s, and the finding that soil staying wet over winter shortens the plant’s garden life is Illinois Extension’s. Both are named in the text, not just used.The single authority for hardiness ranges. When the map is revised, entries affected by the revision are rechecked rather than left carrying the old range.
Used for: hardiness zones, overwintering guidance In practice: every zone range on the site is stated against this map rather than against a nursery’s claim. Lavender is recorded as zones 5 to 9, with the entry saying what to do below zone 5 instead of leaving the range to imply it.The reference most American pet owners are actually pointed to by their vet. Toxicity is quoted from it rather than summarized, because a paraphrase of a pet safety warning is worth nothing to the person reading it at eleven at night.
Used for: toxicity to dogs, cats and horses In practice: the lavender toxicity field carries the listing rather than a summary of it, naming linalool and linalyl acetate as the toxic principles and nausea, vomiting and loss of appetite as the signs. That is what a vet asks for.What is never a source
Other gardening websites, content farms, retailer product descriptions, nursery marketing copy, and answers produced by a language model. Not as a primary source and not as a check on one.
This is a harder rule than it sounds, because the copied number is always the easiest number to find. It is also the reason the same plant carries five different hardiness ranges across the first page of results.
A value that appears on twenty websites has been verified zero times. It has been copied nineteen times.
When two sources disagree
They regularly do, and usually for a good reason: extension services are regional, so two of them can both be right about their own region and appear to contradict each other.
- Where the difference is regional, the entry gives the range that covers both, and says which conditions push it to each end
- Where one source is materially more recent and the difference is not regional, the recent one is used
- Where the disagreement cannot be resolved that way, the entry says so in the field rather than picking a winner silently
How a value gets recorded
Four rules govern what actually lands in a field.
The core fields
Every entry, regardless of section, answers these. Section-specific fields are added on top: houseplants gain humidity and repotting, vegetables gain sowing depth and days to harvest.
| Field | Recorded as | Source tier |
|---|---|---|
| Light | One of four values, plus the hours behind it | Tier 1 |
| Water | Low, moderate or high, plus a frequency in plain words | Tier 1 |
| Hardiness | Zone range, or annual where it does not apply | Tier 2 |
| Soil | Texture and drainage, plus pH range where it matters | Tier 1 |
| Mature size | Height and spread, both as ranges | Tier 1 |
| Bloom time | Season range, stated for a named zone | Tier 1 |
| Toxicity | Quoted from the listing, with the species named | Tier 3 |
| Lifecycle | Annual, biennial, perennial, shrub or tree | Tier 1 |
Review cadence
Every entry carries the date it was last checked against its sources, printed on the page rather than buried in metadata. That date changes when the entry is actually rechecked, and not when a word is edited or an image is swapped.
An entry is rechecked when a source it depends on is revised, when a correction arrives, or on a rolling schedule so that nothing sits unexamined indefinitely. A publish date bumped forward to look fresh is the oldest trick in this category and we are not doing it.
Illustrations
Plant imagery on this site is illustration, labeled as illustration on every page that carries it. It is not evidence of a variety, a place or a season, and it is never captioned as though it were.
This is a deliberate constraint rather than an apology. A photograph implies a specific plant on a specific day. Where we cannot honestly make that claim, we do not imply it with a caption.
Corrections
Corrections are the part of a method that proves the rest of it. Ours works like this:
- Send the entry, the field you believe is wrong, and the source for the right value
- We check it against the tier above, not against your source alone
- If the correction holds, the field changes and the entry’s review date changes with it
- If it does not hold, you get the reason and the source we relied on
Corrections that arrive with a source are acted on far faster than corrections that arrive as an assertion, for the same reason the whole site exists.
What we do not claim
This is a horticultural reference. It is not veterinary advice, not medical advice, and not a substitute for either.
Toxicity entries quote a listing so you can act on it, usually by calling a vet. They do not tell you what will happen to an animal that has eaten something, because that depends on the animal, the quantity and the timing, and nobody should be making that call from a plant care page.
Both, at different levels. The prose on an entry names the publication a statement came from, so a claim about pruning or drainage can be traced to the extension service that made it. The recorded field values are governed by the hierarchy on this page rather than repeated citation, because the same three tiers supply every entry in the same order.