Fully blooming pink cosmos.
image by Sorayui, Morguefile
Choosing plants for your landscape also involves picking flowers that help the garden's animals and insects. Cosmos offers a beautiful, hardy flower and a favorite snack for birds and butterflies. This plant prefers full sun but can tolerate partial shade. However, cosmos prefers well-drained soil and does well in soil that hasn't been enriched with organic materials. It produces abundant seeds as the stalks die with the onset of cool weather.
Choose a spot with well-drained soil in full sun or partial shade (six hours each day) after the final frost of the season. Cosmos grows 1 to 6 feet tall, so it shouldn't be used as a border planting.
Dig holes for each plant that are about 1 foot apart and deep enough to allow the top level of the root ball to lie 1-inch below the garden surface. Don't add any soil amendments such as humus, peat or compost to the soil. Cosmos prefers soil with a neutral pH and little organic matter.
Tip the pot on its side and press on the plastic pot. Rotate the pot carefully and continue pressing on the outside of the pot to loosen the plant and potting soil. This prevents damage caused by tugging the plant out of the pot by the stem. If this method doesn't work, cut the plastic pot with pruning clippers.
Loosen the root ball by working your fingers gently into the outer layer of potting soil that surrounds the roots. This frees root-bound plants to encourage outward root growth.
Place the plant into the hole, firming the soil around the plant until the dirt reaches the garden surface.
Water the cosmos at the base, enough to keep the soil slightly damp until the plant becomes established.
Prune flowers after initial blooming in mid-August to encourage another round of blooming later in the fall. Cosmos will self-seed easily at the end of the growing season, so leave any dry flowers and stalks in the garden. Birds will nibble on the seeds and the plant can double in size from this self-seeding.