Delphinium, also known as larkspur, is a perennial prized for its tall flower spikes, made up of blue, mauve, pink or white flowers. It is ideal for adding height and colour to your garden. Sowing delphinium is fairly tricky to get right and can produce variable results, but by following our advice you should have no trouble. Young plants obtained are rarely true to the parent, which can give great variability in colour, unless you propagate botanical delphiniums. In this tutorial, we will guide you step by step to succeed in your delphinium sowing in pots or directly in open ground.
Sowing delphinium in pots
When to sow delphinium in pots?
Sowing in pots is done in late winter, around March.
How to sow delphinium?
Here are the steps to follow to sow delphinium seeds:
- Take pots or a seed tray, and fill them with seed compost. Firm compost gently to remove air pockets.
- Sow delphinium seeds on surface of compost, spacing them about 2 cm apart.
- Sprinkle a thin layer of compost over the seeds, about 5 mm thick. Delphinium seeds need light to germinate, so do not bury them too deeply.
- Water gently using a spray bottle to avoid displacing them. Compost should be moist, but not waterlogged.
- Cover pots with a clear lid or a mini-greenhouse to retain moisture.
- Place them in a bright spot, but not in direct sunlight. Delphiniums prefer an ambient temperature between 15 and 20°C to germinate.
Care after sowing
- Monitor compost moisture closely and water as needed to keep it evenly moist. Take care not to overwater.
- Ventilate daily by opening the mini-greenhouse or removing the lid
- Delphinium seeds generally take between 7 and 21 days to germinate. Once first shoots appear, remove plastic film or lid to allow better air circulation.
- When delphinium young plants have developed two true leaves, it's time to thin out. Remove the weakest and smallest young plants, keeping only the most vigorous spaced at least 5 cm apart.
Necessary equipment
- Delphinium seeds. It is best to use fresh seeds, as they have high seed viability during the year following harvest, but germinate much less well afterwards. Store them in the refrigerator before sowing if possible: they germinate better after exposure to cold.
- Quality seed compost
- Pots
- A clear lid or a mini-greenhouse to retain moisture
- Labels to mark varieties
- A spray bottle
Sowing delphinium in open ground
When to sow delphinium in open ground?
Sowing delphinium in open ground is done in spring, in April–May.
How to sow delphinium in open ground?
Choose a sunny site with fertile, deep, cool and well-drained soil. Delphiniums prefer neutral or slightly alkaline soil.
- Start by preparing the soil by working it to a depth of at least 30 cm and removing weeds and stones. Add well-rotted compost or manure to improve soil quality and enrich the planting area.
- Then refine the seed bed with a rake to obtain a flat, even surface.
- Sow delphinium seeds, spacing them about 2 cm apart. You can create rows spaced 30 to 60 cm apart, depending on expected size of mature plants.
- Sprinkle a thin layer of compost over the seeds, about 5 mm thick. Delphinium seeds need light to germinate, so do not bury them too deeply.
- Water gently the seeds with a watering can fitted with a rose, to avoid displacing them. Soil should be moist, but not waterlogged.
Delphinium seeds generally take between 7 and 21 days to germinate. Monitor soil moisture and water as needed to keep it evenly moist.
When delphinium young plants have developed two true leaves, it is time to thin out. Remove the weakest and smallest young plants, keeping only the most vigorous spaced at least 30 to 60 cm apart, depending on variety.
Continue to water plants regularly to keep soil slightly moist. Apply a balanced fertiliser in spring and summer to promote healthy growth and abundant flowering.
Necessary equipment
- Delphinium seeds: use fresh, recently harvested seeds if possible, and store them in the refrigerator before sowing.
- To work the soil before sowing: a spade or digging fork, and a rake
- Optionally, a seed sower
- Multi-purpose compost
- A watering can with rose attachment
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