It often feels strange to be collecting seed heads so early into summer; an activity more commonly associated with autumn. However, it’s the early setting biennials that very often have the showiest form once in seed, especially in the long border.
There is, therefore, a good argument for leaving them in place; providing a new element of form and, it could also be suggested, colour to the planting. On a recent trip to Sissinghurst gardens in Sussex, I was struck by the wash of silvery-grey resulting from large, spent Christophii Alliums running through the borders. The same also at Great Dixter (one element of planting design they do appear to agree on).
I have decided to collect my seedheads instead this year for the duel purpose of propagation and (very) early Christmas-season preparation. For the opium poppies now is the time for selecting and storing seed; before they spread themselves far beyond reasonable management and control. And for the alliums, the current dry run has rendered them stiff and easily pulled; so best to seize them before the rains come. As they inevitably will.