How to Grow Cornflower

Start cornflower seeds either outdoors, after the last frost date in your area, or indoors, one month before the last frost date, in plug trays of moist seed starting mix – one to two seeds per plug, covered with ½ inch of the mix. Cover the tray with plastic wrap to ensure high humidity and place it on a heat mat set to 75 degrees Fahrenheit. The seeds should germinate within seven to 10 days. Remove the plastic wrap when they sprout.

Move the seedlings off the heat mat and into an area that receives indirect sunlight after germination. Keep the mix moist at all times. Transplant the cornflower seedlings into the garden when they have their third set of leaves.

Choose a spot in the garden that receives full sun or, if summers are scorchers where you live, choose a spot that is shady in the afternoon. Dig a 1- to 2-inch layer of compost into the garden soil and rake the bed until it’s level.

Dig planting holes that are to the depth that the cornflowers are currently growing and 12 inches apart. Remove the seedlings from the plug tray, saving the strongest and discarding the weakest, and place the root balls in the holes. Cover the roots with soil and use your hands to firm it carefully around the base of each seedling.

Water the seedlings slowly to the depth of their roots and water again whenever the soil is dry to a depth of 6 inches. Avoid watering too often because the cornflower’s stem will become weak and floppy. Unless conditions are hot and dry, continue watering weekly.

Fertilize cornflowers once a month while they are in bloom. Use a balanced fertilizer, such as 10-10-10, at a rate of 1 cup per 25 square feet of garden space. Sprinkle the fertilizer on the soil around the cornflowers and water to a depth of 6 inches.

Snip dead flowers from the cornflower plants to force them to keep blooming. Use clean pruning shears or scissors to snip the stem off at its base.

Inspect the cornflower periodically for aphids – small green or white pests that suck the juices from the plant. Use a strong spray of water from the hose to wash then off the cornflower.

Check the plant for rust and powdery mildew during periods of wet weather. Rust symptoms appear as small orange or yellow blisters on any green part of the cornflower; powdery mildew appears as a white, talc-like substance, typically on the succulent parts of the plant. Avoid these diseases by watering the cornflower at the soil and not overhead and allowing proper air circulation through proper spacing. Remove infected parts of the plant and dispose of them. Spray the cornflower with a ready-to-use fungicidal soap spray. Ensure that all parts of the cornflower plant are covered with the spray and repeat every 10 days, or according to fungicide's label.