Delphinium
An ornamental plant, planted March to June, or sown March to June or August to October.
In September: cut back the delphinium. It can be sown outdoors now.
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Delphinium, month by month
Bar: the usual months. Sprout: this month.
| Sowing, planting or job | Sep | Oct | Nov | Dec | 2027Jan | Feb | Mar | Apr | May | Jun | Jul | Aug |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow under cover. | none | none | none | none | none | none | usual | usual | none | none | none | usual |
| Sow outdoors. | usual | usual | none | none | none | none | none | usual | usual | usual | none | none |
| Plant out. | none | none | none | none | none | none | none | none | none | usual | none | none |
| Plant a pot-grown delphinium. | none | none | none | none | none | none | usual | usual | usual | usual | none | none |
| Cut back the delphinium. | usual | usual | usual | none | none | none | usual | usual | usual | none | none | none |
| Lift and divide the delphinium. | none | none | none | none | none | none | usual | none | none | none | none | none |
| Mulch the delphinium. | none | none | none | none | none | none | usual | usual | usual | none | none | none |
| Stake the delphinium. | none | none | none | none | none | none | usual | usual | usual | none | none | none |
| Deadhead the delphinium. | none | none | none | none | none | none | none | none | none | usual | usual | none |
| Cut the delphinium back hard after flowering. | none | none | none | none | none | none | none | none | none | usual | usual | none |
What to do, and when
The usual months for a UK garden. Your own plan gives the week.
Sowing and planting
Sow under cover March to April, and August, 3mm deep. Moderate sources: Thompson & Morgan and Sarah Raven.
Sow outdoors April to June, and September to October, 0.3cm deep, 25 to 30cm apart. Moderate source: Mr Fothergill’s. Weaker sources for the spacing and the depth: Eden Brothers and Gardening Know How.
Plant out in June, 60cm apart. Strong sources: RHS and Sarah Raven.
Plant a pot-grown delphinium March to June, 60cm apart. Strong sources: RHS and Sarah Raven.
Cut back the delphinium
Once it has finished flowering, cut the whole plant back down to the ground. From Gardeners’ World.
Usually March to May, and September to November. Moderate source: RHS.
Lift and divide the delphinium
Every 2 to 5 years, not every year.
Usually March. Strong source: RHS.
Mulch the delphinium
Spread 5cm of garden compost or farmyard manure around the outside of the clumps.
Usually March to May. Strong source: RHS.
Stake the delphinium
Use canes for taller varieties, or a frame the plants can grow up through.
Usually March to May. Moderate source: Gardeners’ World.
Deadhead the delphinium
Usually June to July. Moderate source: Sarah Raven.
Cut the delphinium back hard after flowering
Gardeners call this the Hampton hack.
Almost to the ground, straight after its first flowers. Fresh leaves follow, and often a second flush of flowers.
Usually June to July. Moderate source: RHS.
What the source words mean
Strong: the RHS page for this plant is among them.Moderate: another trusted UK source, or the RHS on its group.Weaker: a blog, a forum, a small website or a page from outside the UK. Treat it as a guide.
Every line above names the page it comes from. Where we found no good source for a job, we left it out. Where the name “Delphinium” comes from.