The scientific name for the cornflower is Centaurea cyanus, but it's also known as bachelor's button or basket flower. The foliage has a greyish appearance due to the tiny white hairs covering the leaves. The small blossoms appear in pink, purple, and white, as well as several shades of blue. They attract butterflies, bees and birds. Most cornflowers are annuals, but a few perennials are available.
Cornflowers will grow in a variety of soil types, but they do best when the pH is neutral or slightly alkaline. Prepare the seedbed by digging in a 1- to 2-inch layer of organic matter. Select a site where the plants will receive full or partial sun. In climates with very hot summers, provide shade during the hottest part of the day.
Sow Seeds in the Garden
Cornflower seeds need to be in the dark to germinate, so plant them 1/2 inch deep. Keep the seedbed moist until the seeds germinate in seven to 25 days. When the seedlings develop true leaves, thin them to 6 to 12 inches. Cornflowers don't mind being a little crowded, but they also need good air circulation
Cornflowers self-sow to a certain degree, but the effect may be spotty, so it's best to plant them annually for a good display. Consider succession plantings every two weeks until midsummer since the bloom period is short.
Start Seeds Indoors
Start cornflower seeds indoors one month before the last spring frost. Sow the seeds 1/2 inch deep in moistened seed-starting mix. Set the containers in a location that remains between 15.6 and 21.1 degrees Celsius and cover them with plastic. Water lightly as needed to keep the seeds moist. Remove the plastic as soon as the seeds germinate and place the containers in a sunny location or under a grow light. When the seedlings develop their first set of true leaves, remove all but one seedling per pot. Transplant the cornflowers before they grow taller than 4 inches, setting them 12 inches apart in the garden.
Grow as Container Plants
Cornflowers do well in containers. As the foliage can look patchy in hot weather, plant them with other annuals that cover the bottom of the cornflower plants. Use lightweight potting mix and ensure adequate drainage. Add slow-release fertiliser pellets before planting the seedlings.
To encourage cornflowers to develop more branches, pinch back the tips. For more flowers, remove blossoms when they begin to wilt. Fertilise cornflowers monthly with a complete fertiliser for flowering plants. Do not overwater cornflowers, as the stems may weaken.
Pests and Diseases
If aphids attack your cornflowers, blast the foliage with water from a garden hose to dislodge them. Cornflowers are susceptible to fungal diseases such as powdery mildew and rust during rainy weather. Providing good air circulation is an effective preventive measure, as is watering the soil rather than the foliage. Control rust with fungicidal soap or sulphur and remove affected leaves.