What is growing under my bird feeder?
Most of what comes up is crop seed from the mix. The plant to check for is a tall, hairless pigweed, because a University of Missouri survey found Palmer amaranth seed in 27 of 98 birdseed mixes. Here is which ingredients carry which weed, how to identify it, and what each state asks you to do.
The short answer
- Most of it is the mix itself: millet grass, milo, sunflower and safflower seedlings. Those are crop plants and pull up easily.
- Weed seed rides along. A University of Missouri team found pigweed (Amaranthus) seed in 94 of 98 birdseed mixes and Palmer amaranth in 27. About 19% of the pigweed seed was ready to sprout.
- The ingredients matter. Proso millet, grain sorghum (milo) and corn raised pigweed contamination; sunflower went with common ragweed and safflower with kochia.
- Palmer amaranth is taller than common pigweed, hairless, with a leaf stalk longer than the leaf and seed spikes on female plants up to 3 ft long. Pull it before it seeds, bag it in black plastic and put it in the trash.
- Washington, Oregon, Montana and Minnesota regulate it, and each names who to report to. Elsewhere, take a sample to your county Extension office.
Mostly the birdseed itself. Coarse grass is millet, and the broad seedlings are sunflower or safflower from the mix. Those are harmless crop plants that die at frost. The plant to look at twice is a pigweed, because weed seed rides in the bag: a University of Missouri survey found pigweed (Amaranthus) seed in 94 of 98 birdseed mixes, and Palmer amaranth, a weed that Washington's agriculture department calls resistant to many herbicides, in 27 of them.
Two answers circulate. Gardening pages say feeder sprouts are just spilled seed and nothing to worry about. Farm press calls the bird feeder a route for superweeds. Both are right about different plants. The millet grass really is harmless. The pigweed is the reason Washington quarantined Palmer amaranth in 2025, and why Montana State University weed scientist Tim Seipel was quoted by GROW saying: "We're moving herbicide resistance across the United States in bags of bird feed."
What the Missouri survey found#
Eric Oseland, Kevin Bradley and colleagues examined 98 commercially available bird feed mixes in 2016 and 2017, counted every weed seed and identified it by species. The paper appeared in Invasive Plant Science and Management on 20 January 2020. The figures below come from its abstract.
| Finding | Result |
|---|---|
| Mixes containing pigweed (Amaranthus) seed | 94 of 98 |
| Mixes containing Palmer amaranth seed | 27 of 98 |
| Pigweed species found | Waterhemp, redroot, Palmer amaranth, smooth and tumble pigweed |
| Other weeds found | Common ragweed, kochia, grain sorghum, wild buckwheat, common lambsquarters, large crabgrass, foxtail (Setaria) |
| Pigweed seed readily germinable in a greenhouse | About 19% |
| Mixes with glyphosate-resistant seed | 5, holding waterhemp and Palmer amaranth seed |
When MU Extension first reported the work in January 2018, it said one pound bag held 8,000 pigweed seeds and that mixes with millet "seem to contain the most weed seeds." At the survey-wide 19%, that bag would put about 1,500 seeds ready to sprout on the ground. That is our arithmetic on two of the study's numbers, not a count anyone made.
Which ingredient carries which weed#
The survey's most useful result for anyone filling a feeder is that the weeds follow the grain. Its regression found that proso millet, grain sorghum and corn in a mix increased pigweed contamination. Millet and sorghum also raised grass weeds. Sunflower went with more common ragweed, and safflower with more kochia.
Put that next to what the seed does on the ground and you get the table that decides what to buy.
| Ingredient | Sprouts itself under the feeder? | Weed seed it raised in the survey | Birds that need it |
|---|---|---|---|
| White proso millet | Yes, vigorously | Pigweed, grass weeds | Juncos, sparrows, doves, on the ground |
| Milo (grain sorghum) | Yes | Pigweed, grass weeds | Few in the East; see birdseed mixes |
| Cracked corn | Yes | Pigweed | Jays, doves, blackbirds |
| Black oil sunflower | Yes, readily | Common ragweed | Nearly every feeder bird |
| Safflower | Yes | Kochia | Cardinals |
| Sunflower hearts | No, the germ is broken | Not reported separately | Nearly every feeder bird |
| Nyjer | No, heat-treated before sale | Not reported separately | Finches |
The sprouting column is from our seed waste and mess page. The weed column is the survey's. Read the bottom two rows carefully: a seed that cannot sprout says nothing about the weed seed packed with it, and the survey published no figures for hearts or nyjer as separate ingredients. What it does show is that a cheap mix built on millet, milo and corn is where pigweed concentrates. That is one more reason the single-seed approach in best bird seed wins, alongside the cost case in seed mix versus single seed.
Is it Palmer amaranth?#
Pigweeds are hard to tell apart, and Montana State University Extension warns that Palmer amaranth has many close relatives in that state. This table combines the Washington State Department of Agriculture's 2023 Pest Alert, the Washington State Noxious Weed Control Board and MSU.
| Feature | Palmer amaranth | Waterhemp | Redroot and smooth pigweed |
|---|---|---|---|
| Hairs on stem and leaves | None; stem smooth and waxy, may turn red | Not given | Fine hairs |
| Leaf stalk (petiole) | Longer than the leaf blade | Not given | Not given; Powell's amaranth: equal to or shorter than the leaf |
| Leaf | Oval to diamond, small spine at the tip, sometimes a white V | Not given | Not given |
| Sexes | Separate male and female plants | Separate male and female plants | Male and female flowers on one plant |
| Seed head | Long and skinny; up to 3 ft on female plants | Long and skinny | Shorter |
| Height | Commonly 6 to 8 ft, can pass 10 ft | Taller than common pigweeds | Shorter |
The "not given" cells are deliberate: the agency pages we read do not describe those features. Waterhemp and Palmer share the two field marks most people use, and MSU's Schutter Lab confirms either species "via PCR testing services." If a plant has separate sexes and a long thin spike, treat it as one of the two and let a lab decide which.
Size it up early. The Noxious Weed Board says Palmer can grow over 2 inches a day, and a female plant can set up to half a million seeds in a season. MU Extension puts the ceiling at 1 million. A male plant sets no seed, which is the one piece of luck in MSU's record from Toole County, Montana: in 2023 "one male plant was found... growing under a bird feeder: likely a contaminant in bird seed." GROW's April 2026 article dates Montana's first bird feeder plant to 2021. MSU's own February 2024 record lists two Montana finds, both in 2023, so we use MSU's date.
What to do, state by state#
WSDA's Pest Alert says Palmer amaranth already causes extensive corn and soybean losses where it is established in the Midwest. In the states below it is new, and each one regulates it.
| State | Status | Who to call |
|---|---|---|
| Washington | First detected 2023; Class A noxious weed (2024); on the plant quarantine list since 9 August 2025, which bans selling, transporting or distributing plants or parts | Sprouts: your county noxious weed board or the state board, (360) 902-1874. Seed you suspect: the WSDA Animal Feed Program |
| Oregon | Found in fields in Marion and Malheur counties in 2024; on the noxious weed quarantine list since | Oregon Department of Agriculture; follow the recall steps below |
| Montana | Restricted seed species: seed known to be contaminated cannot be sold in the state | Your county Extension office or agronomist, or the state Department of Agriculture's Palmer amaranth task force |
| Minnesota | Prohibited weed seed and on the Prohibited Noxious Weed Eradicate List: all plant parts must be destroyed | Arrest the Pest, 1-888-545-6684 |
| Anywhere else | Varies | Your county Extension office; MU Extension offers its ID Weeds app and Plant Diagnostic Clinic |
Washington's case shows how this happens. In August 2025 a Spokane County weed board specialist found a 3 ft Palmer plant with seedlings in a supermarket parking lot where a shopper had scattered birdseed. Genetic testing of the store's birdseed confirmed Palmer seed, and a 7 lb songbird blend was recalled in Washington and Oregon on 19 September 2025. In February 2026 GROW reported waterhemp seed in several Washington birdfeed brands, the species' first documented presence in the state.
If you find one#
The recall instructions from the Oregon and Washington agriculture departments work for any suspect plant:
- Photograph it first. Stem, a leaf with its stalk, and the seed head. Minnesota asks for the stem and inflorescence.
- Pull it before it flowers if you can, roots and all, straight into a black plastic bag, and put the bag in the trash. Never in the compost.
- Empty the feeder. Double-bag any loose seed for the trash, again no compost.
- Clean the feeder to get the last seeds out, using the routine in how to clean a bird feeder.
- Report it using the table above.
- Watch the spot for five seasons. MU Extension and the Washington board both say the seed can stay viable in soil up to five years. That watch period is our inference from their figure.
Then cut what reaches the soil. Feed millet only on a ground tray or a platform you sweep daily, run hearts over beds and borders, and bag raked hulls rather than composting them. The same swept ground stops feeding the rats and mice and voles that spilled grain draws.
- Top-tier favorite for: Mourning Dove, Dark-eyed Junco, White-throated Sparrow, Song Sparrow, House Sparrow, Red-winged Blackbird
- Eaten readily by: Eastern Towhee, Common Grackle
- Taken occasionally by: Northern Cardinal, House Finch, Purple Finch, European Starling
Dropping millet costs you mainly the ground birds above, so a swept tray is usually a better answer than giving it up.
Where this page stops#
- One survey, abstract only. We quote the Missouri paper's abstract, not its full tables, so we give no per-brand or per-state figures. The bags were bought in 2016 and 2017, and nothing we found says how today's bags compare.
- Germination is a greenhouse number. The 19% was measured in a greenhouse assay, not under a feeder.
- State rules move. Washington listed Palmer in 2024 and quarantined it in 2025, and other states may follow. Check your state agriculture department before you act on the table.
- Not every pigweed is Palmer. Redroot and smooth pigweed are the common lookalikes, and a pigweed with fine hairs on its stem and leaves is not Palmer.
Moldy seed is the other thing that grows under a feeder, and moldy seed covers it. Every other feeder problem is matched to its cause on the problems hub.
Frequently asked questions#
Is the grass growing under my bird feeder harmful?
Usually not. Coarse grass under a feeder in summer is almost always white proso millet, and broad-leaved seedlings in pairs are usually sunflower or safflower from the seed itself. Those are crop plants: annuals that die at frost and pull up in handfuls. The plant worth a second look is a pigweed, an upright plant with alternate oval to diamond leaves and a long seed spike. Weed seed rides in birdseed mixes, and a University of Missouri survey found pigweed seed in 94 of the 98 mixes it tested.
How can I tell if it is Palmer amaranth?
Check three things. The stem and leaves are hairless, where redroot and smooth pigweed have fine hairs. The leaf stalk (petiole) is longer than the leaf blade. And the plant is either all male or all female, and female plants grow seed spikes up to 3 ft long. Waterhemp shares the separate sexes and the long thin heads, and Montana's diagnostic lab confirms either species by PCR testing, so a lookalike is a lab question. Photograph the stem, a leaf with its stalk and the seed head before you pull it.
Should I put weeds from under my bird feeder in the compost?
No. Oregon's and Washington's agriculture departments told owners of contaminated seed to pull sprouted weeds into black plastic bags and put them in the trash, and to double-bag leftover seed for the trash with no composting. Pigweed seed can survive up to five years in soil, so anything that reaches the ground is a five-year problem. Treat spent seed and raked hulls the same way.
Which bird seed will not grow weeds?
Hulled sunflower hearts and heat-treated nyjer will not sprout themselves, as our seed waste page explains. That is not a guarantee the bag holds no weed seed: the Missouri survey did not report on hearts, and it found that sunflower in a mix went with more common ragweed seed. What the survey did show is where pigweed concentrates: in mixes with proso millet, grain sorghum (milo) and corn. Cutting those, or feeding them only on a tray you sweep, cuts the risk most.
Sources and further reading
- Examination of commercially available bird feed for weed seed contaminants. Invasive Plant Science and Management 13(1):14-22 (published 20 January 2020) Eric Oseland, Mandy Bish, Christine Spinka and Kevin Bradley, University of Missouri (abstract; full text paywalled) 98 mixes examined 2016-2017; Amaranthus in 94, Palmer amaranth in 27; about 19% of Amaranthus seed readily germinable; five mixes with glyphosate-resistant waterhemp and Palmer seed; proso millet, grain sorghum and corn increased Amaranthus; millet and sorghum increased grass weeds; sunflower increased common ragweed, safflower kochia
- MU researcher finds pigweed in birdseed and pollinator mixes (2 January 2018) University of Missouri Extension A pound bag held 8,000 seeds; mixes with millet seem to contain the most weed seed; up to 1 million seeds per plant; viable in soil up to five years; ID app and Plant Diagnostic Clinic
- Washington and Oregon issue recall for wild birdseed containing invasive quarantined weed seeds (19 September 2025) Oregon Department of Agriculture 7 lb songbird blend recalled in WA and OR; found by a Spokane County Noxious Weed Board employee, confirmed by genetic analysis; empty feeders, double-bag seed for the trash, no compost, clean feeders, pull sprouts into black plastic bags; detections in Marion and Malheur counties 2024 and Oregon quarantine
- Palmer amaranth (plant quarantine page and Pest Alert AGR 809-769a, October 2023) Washington State Department of Agriculture First detected in WA 2023; quarantine list 9 August 2025; birdseed questions to the Animal Feed Program, sprouts to county noxious weed boards; Pest Alert: 6 to 8 ft, up to 10 ft or more, hairless leaves, petiole longer than leaf, female spikes up to 3 ft, separate male and female plants
- Palmer amaranth Washington State Noxious Weed Control Board Class A noxious weed, listed 2024; leaf-tip spine; up to half a million seeds a season; viable up to 5 years; can grow over 2 inches a day
- Monthly Weed Post, February 2024: Palmer amaranth and waterhemp update Noelle Orloff, Montana State University Extension Two Montana records, both 2023: Daniels County field and, earlier, one male plant under a bird feeder in Toole County; restricted seed species; taller with longer, skinnier inflorescences; dioecious; PCR confirmation
- Crisis at the bird feeder: Palmer and waterhemp move west through contaminated seed (21 April 2026) Amy Sullivan, GROW (Getting Rid Of Weeds) Spokane parking lot population, August 2025; waterhemp confirmed in Washington birdfeed, February 2026; one distributor supplies multiple brands; Seipel quote
- MDA finds Palmer amaranth in feed screenings (22 April 2019) Minnesota Department of Agriculture Prohibited weed seed; Prohibited Noxious Weed Eradicate List, all plant parts destroyed; report to Arrest the Pest 1-888-545-6684