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Will black-oil sunflower seed shells left by birds below the feeder inhibit flowering of plants in the garden? I had planned to add these shells to my compost. Will this cause problems in the garden?

Black-oil sunflower is the hands down favorite food of birds at feeders in winter. However, sunflower hulls dropped to the ground can have an allelopathic effect on other plants and can cause wilting, discoloration, death, etc. Allelopathy is the chemical inhibition of the germination or growth of another plant, and it is a complex phenomenon. Some plants may be affected by a toxic compound produced by one plant, while others are not. The most common allelopathic interaction we think about is black walnut inhibiting growth of many plants grown near it. The toxic effect can be transferred to other plants in various ways; a substance can volatilize or be transferred by water leaching toxic compounds out of leaves or twigs, for example. Such is the case with sunflower; the toxic compound is leached from the shell.

Sunflower shells can be added to compost, where they will break down over time. If you have a "slow" compost pile that doesn't generate much heat, then the compound will break down slowly over time. If your pile is hot and you actively manage it, the compound will break down more quickly.

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