Delphiniums are not native to the UK but have become rooted as the towering stars of garden beds and borders thanks to their tall spires of jewel-toned blooms. These dramatic perennials are happy in the UK’s cool climate, and gardeners who choose to grow them are rewarded with a bright display that catches the eye from May through early July.
But with the flowering season coming to an end for these “magnificent” blooms, as described by English cook and writer Sarah Raven, it’s important to focus on a few gardening tasks. Sarah notes that with the right care now, delphiniums “will often have a second flush of blooms in August and September”.
Sarah says the flowers won’t just appear. She suggests that gardeners get out in the garden soon to encourage a late summer flush.
Simple pruning is all that’s required – it’s a straightforward mix of deadheading and cutting back.
The gardening expert instructed: “Cut back delphiniums, right to the ground, leaves as well as old flower spikes. If you do this now, almost all plants will give you a second flush of flowers in August and September.”
While June is the best time to cut back delphiniums, some plants may still be in full bloom now that it’s July. In this case, wait for a few clear indicators that the plant is on its way out to avoid wasting a bright display.
When to deadhead delphiniums
The consensus is clear on exactly when to cut these impressive blooms back.
“After the first flush and when the flowers have faded and are looking a bit tatty,” said Sarah.
Use a pair of sharp, clean secateurs to cut the flowering spikes right down to the ground, leaving the foliage in place.
“It feels harsh, but if you cut back you’ll get a second flush of flowers in August and September,” said the gardening expert.
Watering is crucial for delphiniums to grow healthy and bright, particularly in the hot weather.
Watering delphiniums
In the summer, delphiniums generally need watering at least once a week, aiming to keep the soil consistently moist but not soggy.
Newly planted delphiniums require more frequent watering, especially in hot, dry weather, possibly every few days to help them establish.
Established plants in containers may also need daily watering during dry spells, as their compost dries out more quickly.
Feeding during the growing season is also often recommended. But, if the soil is reasonable, The Sunday Gardeners suggests you can get away with not feeding them.
They noted: “Whilst summer feeding may not be essential, staking is. This means that if you don’t have time to feed and stake Delphiniums, the more important task is to stake them so the plant and blooms are supported.”