Coreopsis may be grown from seed sown early indoors and transplanted outside after frost, or sown directly in the garden in summer, or grown from potted plants.
Sowing Seed Indoors:
- Sow indoors 6-8 weeks before outdoor planting time
- Sow ½ inches deep in seed-starting formula
- Keep the soil moist at 70-75 degrees F
- Seedlings emerge in 15-20 days
- As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
- Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
- If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 2 pairs of true leaves before transplanting to the garden so they have enough room to develop strong roots.
- Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.
Sowing Directly in the Garden:
- Choose a location in full sun with well-drained soil after danger of frost. In frost free areas sow from fall to early spring.
- Remove weeds and work organic matter into the top 6-8 inches of soil; then level and smooth.
- Sow evenly and thinly cover with ½ inch of fine soil.
- Firm the soil lightly and keep it evenly moist.
- Seedlings will emerge in 15-20 days.
- Thin to 18 inches apart when seedlings are 2 inches tall.
Planting Potted Plants:
- Choose a location in full sun with well-drained soil.
- Prepare the bed by turning the soil under to a depth of 6-12 inches removing any debris, and lightly raking as level as possible.
- The addition of organic matter (leaf mold, compost, well-rotted manure) benefits all gardens and is essential in recently constructed neighborhoods.
- Plant on a cloudy day or in late afternoon to reduce transplant shock.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Unpot the plant and gently loosen the root ball with your hands to encourage good root growth.
- Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand.
- Use the plant tag as a location marker.
- Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water and reduce weeds.
