Research
Where the plant authorities disagree
We verify every plant in the BloomsEye library against the published pages of the major botanical authorities: NC State Extension, Missouri Botanical Garden, the RHS, Clemson, university extensions across the US, and more. Doing that at scale produced a byproduct nobody sets out to build: a precise record of where those authorities contradict each other.
This page is that record. 700 garden plants, 5,556 plant-and-trait checks, built from 16,199 source citations across 4,294 pages on 571 sites. The dataset is free to download at the bottom.
- 700garden plants checked
- 5,556plant-and-trait checks
- 16,199source citations
- 53.7%of plants split on hardiness zones
The headline: hardiness zones are contested, not settled
Across everything we checked, the authorities disagree outright on 555 of 5,556 records, one in ten. But the disagreement is not spread evenly. It concentrates almost entirely in one field, the one gardeners treat as the most settled fact of all:
Hardiness zones split on 374 of the 697 plants we checked: 53.7%. Counting only the plants where the sources gave an answer at all, 74.9% of zone records are a disagreement. When you look up "what zone is this plant hardy to" on two flagship institutional sites, the odds are roughly three in four that they do not match.
Sizes are contested too, more quietly: published spread figures disagree on 14.6% of plants, height on 7.7%. Sun requirements almost never split; across 697 plants we found exactly one disagreement.
- Hardiness zones53.7% · 374 of 697
- Mature spread14.6% · 102 of 697
- Mature height7.7% · 54 of 697
- Sun needs0.1% · 1 of 697
Share of checked plants where the published authorities split outright, by field.
Five disagreements worth staring at
Climbing hydrangea: the Americans and the British, four times apart
NC State and Missouri Botanical Garden both publish a spread of 5 to 6 feet. The RHS publishes 4 to 8 meters: 13 to 26 feet. Same species, flagship institutions on both sides of the Atlantic, and the ranges do not touch.
Who says what- NC State Extension Plant ToolboxWidth: 5 ft. 0 in. - 6 ft. 0 in.
- Missouri Botanical Garden Plant FinderSpread: 5.00 to 6.00 feet
- Royal Horticultural SocietyMax Spread 4-8 metres
- Fast Growing TreesMature Width : 2-4 ft.
- The Tree CenterMature Width: 5-6 ft
Sweet autumn clematis: three answers that never overlap
Plant Addicts sells it at 2 to 3 feet of spread. Fine Gardening says 6 to 10. NC State and Missouri Botanical Garden say 15 to 30. A gardener planning a trellis gets three incompatible answers from three reputable pages, ten times apart end to end.
Who says what- NC State Extension Plant ToolboxWidth: 15 ft. 0 in. - 30 ft. 0 in.
- Missouri Botanical Garden Plant FinderSpread: 15.00 to 30.00 feet
- Fine Gardening plant guidePlant Width : 6 to 10 feet
- Plant AddictsMature Width: 2 - 3 Feet
Periwinkle: eight authorities versus one, and both are right
NC State, Missouri Botanical Garden, Clemson, Illinois, Iowa State, the RHS, American Meadows and Patuxent all put Vinca minor at ankle height, 3 to 6 inches. The University of Missouri's IPM page says up to 6 feet "if given support." The outlier is describing the trailing vine climbing, not the groundcover. No average could fix a disagreement about which question is being answered.
Who says what- NC State Extension Plant ToolboxHeight: 0 ft. 3 in. - 0 ft. 6 in.
- Missouri Botanical Garden Plant FinderHeight: 0.25 to 0.50 feet
- Clemson Cooperative Extension HGIC 1112Vinca minor grows about 6 inches tall
- University of Illinois Extension Hort AnswersMature Height 3-6 Inches
- Royal Horticultural SocietyMax Height 0.1-0.5 metres
- American MeadowsMature Height 4-6" tall
- Iowa State University Extension Yard and GardenCommon periwinkle grows 3-6 inches tall and spreads over 2 feet.
- University of Missouri IPM, Fall Gardentrailing vine that can reach up to 6 feet in height if given support
- Patuxent NurseryThis perennial reaches a height of 3–6 inches and spreads 18–24 inches per plant
Lady of Shalott: the breeder disagrees with itself, correctly
David Austin's own US store sells this rose at 5 feet on its shrub page and 8 feet on its climbing page. One cultivar, sold trained two ways, at two honest sizes. Four plants in our library carry this dual-form finding; all four are David Austin roses.
Who says what- David Austin Roses (US store) - shrub pageshrubHeight: 5ft
- David Austin Roses (UK store)shrubHeight: 4ft (125cm)
- Heirloom Rosesshrub5' x 4'
- Menagerie Farm and FlowershrubHeight: 5 feet
- Grace Rose FarmshrubHeight: 5-6'
- Rosarium Lottum (Netherlands)shrub100-150 cm ( Busch Rose ) or as a small climbing Rose (200-300 cm )
- David Austin Roses (US store) - climbing pageclimberHeight: 8ft
Garden phlox: a flat yes or no on fragrance
Missouri Botanical Garden and NC State both describe Phlox paniculata as fragrant. Go Botany, the Native Plant Trust's flora, says the plant "does not have much of a smell." All three pages name the identical species.
Who says what- Missouri Botanical Garden Plant Finder (Phlox paniculata, the plain species)Flower: Showy, Fragrant
- NC State Extension Plant Toolbox (Phlox paniculata)Lavender-pink fragrant flowers with a long bloom period
- Go Botany, Native Plant Trust (Phlox paniculata)the plant does not have much of a smell
Why the authorities disagree
Reading hundreds of these splits, the reasons sort into a short list, and most of them are nobody's error:
- Different conventions in the same field. Basil is zones 2-11 at Missouri Botanical Garden, 10a-10b at NC State, 3-11 at IFAS. One convention encodes "grown everywhere as an annual," the other "perennial only in the tropics," and both get written into the same box.
- Different horizons. NC State and Missouri Botanical Garden give trumpet vine 4 to 10 feet of spread; Purdue says 40 or more. One is a garden-bed figure, the other is what the vine does over decades if nothing stops it.
- Different questions. The periwinkle case: groundcover height versus supported length.
- Different climates. RHS figures describe plants growing in Britain; American extensions describe the same species in American summers. The climbing hydrangea gap lives here.
- And sometimes, plain contention. The one-zone institutional split is the modal case in the data: Missouri Botanical Garden and NC State give coneflower zones 3-8, Clemson says 3-9.
What we do about it
When the authorities disagree, BloomsEye does not average, and does not pick a favorite. The verification pipeline requires exact consensus before it will touch a stored value; a split is recorded as a split, the plant's page keeps its curated value, and the contested record is what you are reading now. Where the sources agree against our stored value, we correct ours and keep the receipt: 683 of the 5,556 records are corrections against our own catalog, and 350 of those are applied and logged in the ledger today. The full verification story, including which plants are checked to which depth, is on our verification page.
The dataset
Everything on this page is one derived, re-runnable artifact:
CSV: one row per plant, per field, per source, with each source's published value and the verdict.
JSON: the same rows plus per-field statistics and method notes.
Cite this dataset BloomsEye, "Where the plant authorities disagree," 2026-08-07, CC BY 4.0.
Derived 2026-08-07 from the live verification file; 700 plants, 10 fields, 16,199 scored citations. Free to use under CC BY 4.0 with attribution to BloomsEye.
Caveats we want you to know before you quote us: zone comparisons require exact consensus, so a one-zone difference at either end counts as a real disagreement; records where sources gave no answer are excluded from the 74.9% figure (they are counted, separately, as insufficient); and annual-convention clashes like basil are included in the split counts because both conventions are genuinely published in the same field.