My parents are haunted by Elder.
The house next door has been empty for around 12 years, it has just been left.
They had one small Elder growing, now the back garden is a forest of Elder, its growing under the roof of my Dads garage, the berries track everywhere and the get pruple spots on teh carpet, it seeds everywhere and my elderly disabled parents are forever pulling up seedlings from there own front and back gardens and even through cracks in the driveway!
In the past Dad has applied deep root, glyphosate and even pays someone to come and chop some of the plants down!
Unless you have space to grow them, please look for one growing in 'the wild' that you could collect theflowers and berries from!