Custer Milkvetch: A Rare Idaho Native Worth Protecting
If you’re a native plant enthusiast with a passion for rare and special species, Custer milkvetch (Astragalus amnisamissi) might catch your attention. This perennial wildflower is one of Idaho’s botanical treasures, though you won’t find it at your local nursery—and there’s a very good reason for that.
What Makes Custer Milkvetch Special
Custer milkvetch is a native perennial that belongs to the legume family, making it a relative of beans, peas, and other nitrogen-fixing plants. Like other members of the Astragalus genus, it likely produces compound leaves and small, pea-like flowers that are characteristic of milkvetches.
Where You’ll Find It (Or Won’t)
This rare gem is native to the lower 48 states but has an extremely limited range—it’s found only in Idaho. Even within Idaho, Custer milkvetch has a restricted distribution, making it a true botanical rarity.
The Rarity Factor: Why This Matters
Here’s where things get serious: Custer milkvetch has a Global Conservation Status of S3, which means it’s considered Vulnerable. This classification indicates that the species is at risk due to its very limited range and small population size. Typically, S3 species have only 21 to 100 occurrences or between 3,000 and 10,000 individuals worldwide.
What does this mean for gardeners? Simply put, this isn’t a plant you should be casually adding to your flower border.
Should You Plant Custer Milkvetch?
The short answer is: probably not, and here’s why:
- Its extreme rarity means it’s not commercially available
- Removing plants from wild populations could harm already vulnerable populations
- Its specific growing requirements are not well documented
- Conservation efforts should focus on protecting existing populations
However, if you’re involved in legitimate conservation efforts or botanical research, and you have access to responsibly sourced seeds or plants (never collected from wild populations), growing this species could contribute to conservation goals.
Growing Conditions and Care
Since specific cultivation information for Custer milkvetch is limited, we can make educated guesses based on related Astragalus species and its Idaho habitat:
- Likely prefers well-draining soils
- Probably adapted to Idaho’s continental climate with cold winters and warm summers
- As a legume, it likely fixes nitrogen and doesn’t require rich soils
- May be drought-tolerant once established
- Specific USDA hardiness zones are unknown, but likely adapted to Idaho’s climate conditions
Better Alternatives for Your Garden
Instead of trying to grow this rare species, consider these more common and readily available native alternatives:
- Purple prairie clover (Dalea purpurea)
- Wild bergamot (Monarda fistulosa)
- Other more common Astragalus species native to your area
- Regional native legumes that provide similar ecological benefits
Supporting Conservation
The best way to help Custer milkvetch isn’t by trying to grow it in your garden—it’s by supporting habitat conservation and research efforts. Consider donating to botanical gardens, native plant societies, or conservation organizations working to protect rare plant species and their habitats in Idaho.
Sometimes the most loving thing we can do for a rare plant is to admire it from afar and let the experts handle its conservation. Custer milkvetch serves as a beautiful reminder that not every native plant belongs in our gardens—some are too precious and rare to risk disturbing.
