There’s no doubt that the very best delphiniums are those propagated by division or cuttings. But it’s impossible to produce them in the large numbers gardeners need by these methods and tissue culture, which works so well for so many perennials like heucheras, campanulas, coreopsis and so on, doesn’t yet work for delphiniums. I’m sure they’ll crack it eventually, but in the meantime the only way to raise delphiniums in the numbers that nurseries and gardeners really need is from seed.
One of the best was ‘Aurora Light Purple’ – lovely colour, good flower form and no off-types – but there’s one big problem with delphiniums from seed: they are very difficult to keep true to colour, superior spike quality and good garden performance. So the trial of seed-raised delphiniums under way at the RHS garden at Wisley is very useful. Even in this first year, it’s clear that some entries are much more uniform than others. There are forty-six in all, and they’ll be judged this year and again next year.
But even if the colour is uniform if the structure of the plant is poor, then it’s still not a good garden plant. ‘Clear Springs Lavender’, for example, produced a lot of lovely, well-formed spikes but the display was spoiled by the secondary spikes growing up around the main spike while it was still at its best. It may sound a like a small thing, but in the garden it makes a big difference.
The trial continues through next year, I’ll report the results when they’re in.