I’ve always been in two minds – maybe more than two – in regard to penstemons.
Yes, they’re generous in bloom, and yes, they come in a good range of colours. They flower for an incredibly long time, provided they don’t get too dry. Indeed they’d likely flower nearly all year in a frost-free temperate climate, with a little summer irrigation.
But I just can’t seem to love them. There’s often too much foliage for the amount of flower they offer, and the foliage is without any distinction, making little or no contribution to a planting. And while I’m a total sucker for tubular flowers that taper up a vertical stem (like foxgloves, for instance), the flowers on too many penstemons are overly chunky and congested, making for good colour presentation but with no grace or elegance.
Enter Penstemon ‘Blackbird’. The foliage has a narrow, willowy quality that earns the plant a few entry-level elegance points. And the flowers are a rare perfect match, presenting as slender tubes that flare open at the end, but with such open, free spacing that you’re more likely to engage with the sides of individual flowers as well as the flared ends, than you do with the fatter-flowered forms, in which you’re much more restricted to looking into their wide-open mouths. In most of these latter forms, the leaves present as a smug tump, and the flowers hover, disconnected, overhead, but with Penstemon ‘Blackbird’, the leaves rise up the vertical flowers stems in places to play a little amongst the flowers, topping out at about 1.2m.
Then, of course, there’s that wonderfully rich plum colouring, undiluted by spots or blotches of white, creating a fabulous bass-note in either a safe and tasteful pink and mauve colour scheme, or a racier, hot one.
All good reasons why, if I’m tempted to (or in the case of unavailability of other stuff, forced to) use a penstemon in perennial plantings, Penstemon ‘Blackbird’ is the only one l ever specify.