Store the seed in the refrigerator in a sealed container until ready to plant. Delphinium seed germination is sensitive to high moisture and temperature. You should use a disease free seed sowing mix to avoid “damping off” to which delphiniums are susceptible. Cover the seed lightly. Sow in 72- to 144-cell trays.
Keep in an airy, light place. Water only enough to keep the surface from drying out. It is very important not to overwater or the seed and/or seedlings will quickly rot.
Germination for most species is best between 18 and 24°C (65 - 75°F). Do not allow temperatures to exceed 26°C (80°F). Once germinated, the seedlings will grow on happily in cooler temperatures. Watering the seed in with a general fungicide can be beneficial in helping to prevent disease problems.
Give a further treatment when most of the seedlings have emerged after about 10 days. (These applications are precautions only but help to reduce damping off when conditions favour the disease).
Pot each seedling individually into a small pot when the first true leaves appear.
It is not necessary to germinate delphinium seed in the dark. But if you do, you must be very careful to remove the seedlings to the light once they are germinated. A delay of just a day or two, when temperatures are warm (say above 18°C) will result in elongated, white seedlings which will stand little chance of survival. It is therefore a good idea to place the seeds in the light after the very first sign of germination. Warm temperatures (21-25°C) give a fast, even germination.
Caring for your plants
Situation:
Full sun preferred but successful in up to 50% shade. Delphiniums are very hardy and tolerant of frosts. They will stand and even benefit from winter freezing. In windy sites, support is necessary.
Soil:
Must be rich as delphinium are gross feeders. Mulch and sheep manure work wonders.
PH neutral 6.5-7.0 but successful over a wide range. Well drained, particularly in warm areas. Delphiniums must not get warm, very wet feet. Keep as cool as possible with thick mulch (sawdust also helps prevent slug and snail attack).
Planting:
Plant in raised beds in Spring & Autumn. Space each delphinium ½ m2 to 1 m2 apart. Wide spacing helps control height; with close spacing plants will grow taller.
Care:
Keep young plants moist. Staking is essential for best results. If grown in a bed, grow through raised, wide netting or other framework. Properly supported delphiniums will stand a lot of wind. Don’t plant right up against a wall - the wind will thrash them.
Plant Maintenance:
After flowering cut each flower spike down to 5 cm above ground; reduce water, gradually increasing again when new growth begins. Cut down and tidy in mid-winter, put slug bait down and mulch. Start feeding again when new growth is 5-10 cm high.
Watering:
Water well when in full leaf and growth is rapid. Take care not to over water when cut down after flowering, but increase water again when new shoots are 5-8 cm high.
Diseases and Pests:
Powdery Mildew can be a problem and regular spraying with sulphur, backed up with a systemic fungicide in hot humid weather, should keep them clean.
Slugs and snails are the only major pests - use slug pellets to control these especially when plants are small and during winter in mild areas.