Larkspur and Delphiniums are beautiful, tall flowers that makes a neat early spring addition to any garden. They used to be in the same family, but Larkspur have since been reclassified to their own family. They do still grow in almost the same way. Start your seeds at least 8-12 weeks before consistent warmer weather. If you live in the south, save half of your seeds to start later in fall. Delphiniums are considered perennials, while larkspur are annuals. In warmer areas, delphinium may be treated as annuals if they don’t have protections from summer heat.
Larkspur seeds need to go through “vernalization”, a period of cold and dark before it can germinate. To achieve this indoors, put moist soil and seeds into a large ziplock plastic bag and put it in the refrigerator for at least 2 weeks (use a seed starting soil mix) - preferably the vegetable crisper drawer. After the cold, you can either grow your seeds in a seed tray in cool darkness, like back in the fridge in a seed tray or individual pots (you’ll need to check these often to make sure they don’t dry out, or cover with plastic) or if you have a dark, cool cellar or closet that can keep them between 40 and 55ºF, they can be kept out of the fridge. If keeping them indoors in the dark, check for growth regularly after the first week. As soon as you see a seedling emerging, move the tray/pot to the light/out of the fridge.
Delphinium also need 2 weeks in the fridge, but after, they can be moved to room temperature (between 65-70ºF). Darkness isn’t required, but can help with germination rates. Again, the moment any growth is seen, it needs to move into the light!
You can also start both in place in the garden, just pick a spot where they will not overshadow other plants, get at least 6 to 8 hours of sun, and they can get afternoon shade in warmer areas. Larkspur and Delphinium grow longer tap roots, so till your garden bed deeply prior to planting outdoors. Space your seeds 6-8” apart, seedlings 10-12” apart. Add stakes for tall varieties.
Seedlings aren’t overly susceptible to freezes and cold, but protect in the event of a long or late hard freeze with mulch/a cover. Once established, larkspur and delphinium don’t need a lot of tending. Add a side dressing of phosphorus when buds begin to appear to promote further blooms. Water at least 1”/week. Delphinium and larkspur can survive somewhat in droughts, but will sacrifice blooms. When the flower stalk is spent, cut to just above the ground and fertilize to promote new shoots. In winter, you’ll do the same thing and add mulch instead of fertilizer. If cutting flowers to enjoy in a vase, cut the flower stalk when 1/3 of the flower buds have opened.