How to Grow Giant Delphiniums

Growing From Seed

• 1

  Start giant delphinium seeds in late winter, around early March. Start the seeds indoors before temperatures warm to at least 55 degrees Fahrenheit outside.

• 2

  Fill 2-inch peat pots with a mix of 2 parts potting soil and 1 part fine- or medium-grit sand. Pour 2 tbsp. of water into each pot to moisten the top 1/2 inch of soil.

• 3

  Sow one giant delphinium seed in each peat pot. Press the seed 1/8 inch deep and cover it with soil.

• 4

  Set the potted giant delphinium seeds on a windowsill with bright but indirect sun exposure. Keep temperatures between 55 and 60 F during the germination process.

• 5

  Watch for sprouting in two weeks. Transplant the giant delphinium seedlings into a draining bed with loamy soil and full to partial sun, depending on the climate.

Growing From Cuttings

• 6

  Grow giant delphiniums from cuttings in spring before the plant blooms or in early summer immediately after the blooming period.

• 7

  Prepare a rooting pot before harvesting the giant delphinium cuttings. Fill a 6-inch plastic pot with a mixture of 2 parts potting soil and 1 part fine sand. Pour 1 cup of water into the pot.

• 8

  Put on gloves before harvesting cuttings from the giant delphinium since the stems and leaves are poisonous.

• 9

  Locate a shoot measuring no more than 3 inches in height. Remove a half-inch layer of soil from the base of the shoot to expose the calloused brown material attached at the bottom.

• 10

  Position the blades of a pair of pruning shears at the base of the shoot. Sever the stem so a 1/4-inch piece of the calloused brown portion remains attached at the base.

• 11

  Apply a thin layer of 0.1 percent IBA rooting hormone to the bottom inch of the cutting. Tap the stem to dislodge any excess hormone.

• 12

  Bury the bottom inch of the giant delphinium cutting in the prepared rooting pot. Push the soil in around the stem to steady it.

• 13

  Place the potted giant delphinium cutting outdoors in a cool, shaded location. Limit direct sun exposure to less than 30 minutes each day.

• 14

  Water the cuttings whenever the soil feels dry 1 inch below the surface. Do not allow the soil to dry out completely.

• 15

  Check for roots in 10 days. Transplant the rooted giant delphinium cutting into a permanent bed with loamy soil about five days after rooting.

Growing From Divisions

• 16

  Grow giant delphiniums from divisions in late spring, around early May. Wait until the plant has finished blooming to divide it.

• 17

  Water the plant to a depth of 3 inches the evening before dividing it. Run a hose at the base of the stems for about 15 minutes.

• 18

  Dig up the entire giant delphinium plant the following morning. Work the blade of a shovel into the soil three inches from the base of the plant. Press the shovel in to its entire length.

• 19

  Pry the giant delphinium plant from the ground. Set it on a flat surface. Crumble off most of the soil from around the roots.

• 20

  Cut the root ball of the giant delphinium into two to four portions of equal size. Use a gardening knife or pruning shears to cut the roots.

• 21

  Plant the giant delphinium divisions directly into a loamy garden bed with good drainage. Plant them so the base of the stems are flush with the surrounding soil.

• 22

  Water the divisions to a depth of 1 inch every three days. Maintain moisture at a depth of 3 inches for the first month before decreasing the water to 1 inch every seven days.