A decision also has to be made about what colours to use in the three big black pots. I love to do something different with them every year. We've had lemon lavender and lime, and burgundy, black and deep pink. I wonder if I paint some canes blue and grow two, maybe three delphiniums in each pot, and squeeze in some blue petunias and lobelia, and if it's not too late to sow them some of that lovely blue annual nemophila Baby Blue Eyes? - watch this space!
That leaves just 18 giant delphiniums to find room for (I'm not rational when it comes to the garden) and there is a mountain of manure in the drive....