Bulbous Bluegrass Poa bulbosa
Bulbous Bluegrass is an introduced perennial grass, found in the lower 48 states. It grows to 1.5 ft and blooms May in full sun – part shade, with brown fruit.
Bulbous Bluegrass is flagged invasive in the U.S. These natives fill a similar niche — same growth habit, bloom season, height, and region — so you keep the look and feed local wildlife instead of spreading a problem.
Part of why it adapts so well: Bulbous Bluegrass is a polyploid complex — multiple chromosome races are on record (2n = 21, 24, 28, 33, 35, 36, 39, 40, 41, 42, 43, 44, 46). Spare genome copies give a plant extra raw material to evolve fast, and polyploidy is a documented correlate of successful plant invasions (te Beest et al. 2012). A labelled association from open cytology (ChromoDB), not a prediction for your specific site.
Growing & care
USDA PLANTS · TRY- Sun
- Full sun – part shade
- Soil & moisture
- Medium moisture
- Soil pH
- 5–7.2
- Fertility need
- Medium
- Adapts to
- Coarse (sandy), Medium (loam), Fine (clay)
- Hardiness
- USDA zone 4+
- Height
- 1.5 ft
- Spread
- None — clumping
- Growth rate
- Moderate
- Growth form
- Bunch
- Lifespan
- Perennial · long-lived
- Foliage
- Broadleaf · fine texture
- Active growth
- Spring & autumn
- Fruit
- Brown persists into winter
- Flower colour
- Green AI AI image-analysis of community-science photos — lower-confidence (a more subjective call, often an inconspicuous flower); not a botanical record
- Propagate by
- Seed
- Seed starting
- No stratification needed
- Seeds ripen
- Summer seed-collection / harvest window
- In the trade
- Routinely available
- Deer browsing
- Low often deer-resistant
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~42 caterpillar species
Poa supports ~42 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 strong genus.
Recorded feeding on Poa in North America, including:
+ 8 more species → ↑ show fewer
Wildlife & visitors 1 nectaring
Open records of who else uses Bulbous Bluegrass — a generalist food-web signal, kept separate from the keystone Ecological Value.
1 adult butterfly & moth species is recorded nectaring at its flowers:
Across 25 U.S. vegetation-survey plots that recorded Bulbous Bluegrass, these catalog species turned up most often in the same plot — a real field co-occurrence signal, not a planting prescription.
Related plants
More Poa →
How we know this (5) Methods & honest limits
We read each species’ measured specific leaf area (leaf area per unit dry weight) from the Global Spectrum dataset and band it: thin & fast (high SLA), medium, or thick & tough (low SLA). The global median is about 10 mm²/mg.
Honest limits: A species-mean from pooled measurements — individual plants vary with light and site. A broad strategy signal, not a precise per-plant figure.
We place each species on Grime’s competitor–stress-tolerator–ruderal (C–S–R) triangle using the globally-calibrated “StrateFy” method: leaf size drives the competitor score, dense low-area leaves the stress-tolerator score, and thin high-area leaves the ruderal score. The result is a C/S/R percentage mix and one of 19 strategy classes; we show it in plain words and keep the percentages for the curious.
Honest limits: A species-mean strategy from pooled global leaf measurements — a broad ecological signal, not a precise per-plant or per-site value. Derived, never a measured fact.
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 (33) 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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