They are an oddity in the garden, striking in some settings. Black plants are the basis for the occasional Goth garden, along with some poisonous plants. I use dark foliage and blossoms for impact in my garden.
Black Plants is the title of a new book by Paul Bonine. Grumpy Gardener gave him a bad review -- well, not Mr. Bonine, but the publisher for insisting Bonine include plants that are not black, showing agapanthus as an example. I agree.
My 'Storm Cloud' is a lovely dark blue, but it isn't black.
Most plants classified as 'black' are actually maroon, or darkest blue, or deep purple. The stems of Purple Swirl Datura are a shiny lacquered black and the buds are very dark.
'Black' Tulips are generally maroon or purple, like 'Queen of Night,' shown here in my garden from a previous year when I still believed I could grow tulips. The light shining on them will vary the color. Late evenings, they do look black.
The closest to true black that I have grown was 'Bowles Black ' violas. The problem with the violas was that I didn't plan well for companions and they kind of faded into the background. Black flowers in a grouping will leave a black hole appearance in the garden from a distance.
Black Pearl peppers are a fun garden oddity. The immature fruit is black, as are the leaves. The blossoms are deepest lovely purple. When the fruit matures, it turns bright red. Red companions are needed with these ornamental peppers. I used Oxblood lilies and Salvia coccinea.
I would not go so far as to call purple foliage black, so despite its great beauty as a companion to other plants, Alternanthera dentata is purple, not black. I used it everywhere, for shadows in the garden. Castor Bean is another purple, I didn't plant it this year because of the puppy.
Colocasia 'Black Magic' makes a good show of blackish leaves; purple in sunlight.
I'm off to thumb through the latest catalogs to find more black plants. What are yours?
The Oregonian video with Mr. Bonine, interviewed by Anne Jaegar.
Oregonian article by Kim Pokorny listing Black Plants