My feeder hangs in a lawn of mostly white clover. Is there a perennial, especially a ground cover, that would survive the toxic effect of sunflower seed hulls? If not, is there any other perennial that would do so?
You have asked a very interesting question. The impact of sunflowers on surrounding plants has been well known for many years. In fact, most of the scientific research has been about the agricultural use of sunflowers’ allelopathic affect on plants to control common weeds! Allelopathy means that plants produce a natural herbicide. Unfortunately, those studies showed that the sunflowers’ effect is not target specific and it was not possible to control weeds without negative effect on the crops.
Not just the seed hulls, but also decaying leaves, root exudates, leaf leachates and the soil in which sunflowers have been grown, can influence the antioxidant systems in nearby plants, causing cell-membrane permeability and cellular damage, reducing the plants’ ability to germinate and causing a gradual loss of seed vigor among other symptoms.
So you are right to be concerned about an accumulation of hulls falling around the base of a bird feeder preventing or retarding the growth of plants in that area. Although some source report that hulls put into an active well-managed compost pile may break down to safe levels in about 2 months, others suggest a much longer period. You are best to dispose of them in the garbage or the city garden waste pick up.
Grasses of all kinds, pole beans and potatoes are especially susceptible to sunflowers’ allelopathy. Various gardeners have reported some resistance in the following plants and they are suggested on an experimental basis, since there is no documented proof of their long term survival:
- black-eyed Susan
- climbing roses*
- day lilies
- heuchera (coral bells)
- lemon balm
- low growing annual sunflowers
- mother of thyme
- periwinkle / vinca*
- purple coneflowers
- tickseed coreopsis
One technique that has been recommended is to plant the sprawling ground covers and long caned or vining plants (indicated with an asterisk above) in the soil OUTSIDE the edges of the bare zone under the feeder and encourage them to trail into it.
Ultimately, you may be best advised to move the feeder to an area you can cover with a hard surface and be vigilant about cleaning up. Although more expensive, shelled sunflower seeds, know as sunflower hearts, will be less messy and easier to clean up. And of course, there is birdseed without any sunflower seeds at all.
I hope you find a way to balance your care for the birds and your garden!