Delphiniums are easy to start from seed and can be started indoors early in the season or directly outdoors once the threat of frost has passed. Starting the seeds indoors will ensure blooming the very first season.
The success of your seedlings will depend heavily on the quality of the seed with which you begin.
Seeds are temperamental little things that require proper handling to remain healthy and viable, which is why most gardeners will meet with success more often if they purchase fresh seeds from a reputable company, rather than attempting to save seed from season to season. Saved seeds can suffer from a variety of issues including being the result of random pollination which means that the seed will not produce the parent plant.
Even when obtaining the highest quality seed, you can expect to see only 65-80% of those germinate. Of that number, only 60-75% will produce healthy, vigorous seedlings that will survive transplanting.
Planting Delphinium Seeds
Purchase seed flats that have been thoroughly cleaned. Sterilize any container that will be used to germinate seeds in a solution of one part bleach to nine parts water.
Use only sterile starter soil that is well-aerated. You can purchase sterile starter soil, or you can make your own by combining one part vermiculite to one part peat moss.
Fill the seed flats with the sterile soil that has been thoroughly moistened. Fill up to 1/4″ from the brim. Pat down lightly.
Press the seeds lightly into the soil and cover with soil. Moisten the seed pot with a sprayer filled with water.
Cover the seed flat in clear, plastic wrap to help keep the soil consistently moist and warm. Delphinium seeds require a soil temperature of 65-75°F to germinate so find a spot where these conditions will be met. Sporadically lift the plastic to allow oxygen in.
Remove the plastic wrap as soon as soon as seedlings emerge. Move to a lightly shaded area. You can transplant to individual pots when the first true leave appear.
Seedlings often benefit from hardening off prior to planting out of doors full time. Hardening off seedlings allow them to become acclimated to the external conditions in short intervals to reduce stress on the plant and help it to withstand the changes in environmental factors.
To harden off, wait until outside temperatures reach at least 45°F or higher. Plan on bringing the seedlings outside at least two weeks before you plan on permanently planting them. Start by placing the plant in a shady location, gradually moving them into sunnier locations. At first, leave outside for only a few hours, gradually leaving outside a little longer each day. Bring indoors every evening.