Purple Milkvetch Astragalus agrestis
Purple Milkvetch is a perennial wildflower native to Canada and the lower 48 states. It grows to 1 ft and blooms Jul in part shade – shade, with brown fruit. A host for pollen-specialist native bees.
More about this plant
Astragalus agrestis is a species of milkvetch known by the common names purple milkvetch, purple loco, and field milkvetch. It is native to much of western and northern North America from most of Canada to the southwestern United States, as well as eastern Asia. It grows in vernally moist areas such as meadows, and is often found in sagebrush. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Part shade – shade
- Soil & moisture
- Low moisture
- Soil pH
- 6.3–7.7
- Fertility need
- Medium
- Adapts to
- Medium (loam)
- Hardiness
- USDA zone 4+
- Height
- 1 ft
- Spread
- Moderate
- Growth rate
- Moderate
- Growth form
- Rhizomatous
- Lifespan
- Perennial · short-lived
- Foliage
- Broadleaf · fine texture
- Active growth
- Spring & summer
- Fruit
- Brown
- Flower colour
- Pink AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
- Propagate by
- Seed
- Seed starting
- No stratification needed
- Seeds ripen
- Summer – Autumn seed-collection / harvest window
- In the trade
- No known commercial source
- Deer browsing
- Medium moderately palatable
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~15 caterpillar species
Astragalus supports ~15 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a moderate genus.
Recorded feeding on Astragalus in North America, including:
+ 8 more species → ↑ show fewer
✦ Bees specialist-bee host · 21 bee visitors
Specialist native bees depend on it.
Some native bees are pollen specialists (oligolectic) — they raise young only on pollen from particular plant genera. Astragalus is a recorded specialist-bee host, so losing it can mean losing the bee that relies on it.
21 native & managed bee species are documented visiting Purple Milkvetch — the 12 most-recorded:
Wildlife & visitors 18 nectaring
Open records of who else uses Purple Milkvetch — a generalist food-web signal, kept separate from the keystone Ecological Value.
18 adult butterfly & moth species are recorded nectaring at its flowers — the most-recorded:
Related plants
More Astragalus →
How we know this (3) Methods & honest limits
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
McKenzie et al. assigned each species a flower colour with a GPT-4V vision model over iNaturalist photos. We use the confident tier plus a separately-labelled lower-confidence top-up (mostly inconspicuous green/brown flowers), and render it as a small tint — never as an asserted fact, and kept out of the written synopsis.
Honest limits: AI image inference (~87% expert agreement on the confident tier); a decorative, confidence-tiered indicator, not a measured trait.
Sources for this entry (36) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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