The appearance of unwanted green shoots beneath a bird feeder is common. Spilled seeds that find purchase in the soil, combined with moisture and warmth, can germinate and grow into unexpected plants. The identity of these volunteer plants is directly linked to the ingredients in the commercial seed mix. Birds often scatter the seeds they do not prefer while foraging, making understanding the seed composition the first step toward recognizing the resulting flora.
Common Components of Bird Seed Mixes
Commercial birdseed blends are formulated to attract a wide variety of species, and their contents determine which plants may sprout. Black Oil Sunflower (BOS) seeds are the most popular component, favored for their high fat and protein content, which provides substantial energy. These seeds have thin shells, making them easy for most seed-eating birds to crack open.
White Proso Millet is another common ingredient, particularly attractive to ground-feeding birds like doves, quail, and juncos. This small, round grain is included in mixes due to its nutritional value and appeal to smaller species. Cracked corn is frequently added as a filler, appealing to larger birds such as ducks and pheasants, but smaller songbirds often toss it aside.
Nyjer seed, often mistakenly called thistle, is a favorite food for finches. Nyjer is imported, and federal regulations require it to be heat-sterilized before sale, effectively preventing germination. Seeds like milo (sorghum) or wheat may also be present as less-preferred fillers that birds discard, increasing the likelihood of sprouting.
Identifying the Resulting Plants
The most recognizable plant to emerge is the sunflower, which grows from the high-oil black or striped seeds. When a sunflower seed sprouts, it first sends up two large, distinct cotyledons, or “seed leaves.” The true leaves that follow are rough-textured and heart-shaped, quickly developing into a tall, coarse plant that may produce multiple smaller flower heads.
Sprouts from millet and corn present a grass-like appearance. Millet (an annual grass) and whole corn kernels produce thin, single blades of foliage similar to lawn grasses in their early stages. The corn plant grows thick, jointed stalks, while millet develops into a finer, multi-stemmed plant that can reach heights of three to six feet.
Other potential volunteer plants include sorghum (milo), which has a stalk and leaves that initially look like corn but produces a dense, compact seed head instead of an ear. Safflower, if present, germinates into a plant with a thistle-like appearance, growing up to five feet tall and producing a yellow, orange, or red globe-shaped flower.
Preventing and Controlling Sprouting
Minimizing unwanted plant growth begins with selecting seed mixes less likely to sprout. Switching to “no-mess” or hulled seeds, such as sunflower hearts, eliminates the outer shell that protects the viable embryo. Since the seed is de-husked, it lacks the protective layer needed to germinate successfully, though these seeds are typically more expensive.
Strategic feeder placement can significantly reduce sprouting issues. Placing the feeder over a hard surface like a patio, concrete, or decking prevents seeds from embedding in the soil and accessing germination conditions. Regularly raking and cleaning up the debris beneath the feeder every few weeks removes spilled seeds and hulls before they sprout.
Using a seed catcher tray attached beneath the feeder is a simple, effective solution that catches discarded shells and seeds. If sprouting occurs, rotating the feeder location periodically prevents the heavy accumulation of seeds in one spot. For persistent problems, covering the area with a thick layer of mulch or installing ground cover plants can help shade the soil and suppress new growth.