WHEN TO PLANT COSMOS

• Direct-sow seeds outdoors once the danger of frost has passed. 
• Alternatively, sow seeds indoors 4 to 6 weeks before your last spring frost date in trays or pots with a good seed-starting mixture. Move them into 5-inch pots as soon as they’re 3 or 4 inches tall.
• Young plants (transplants) can be planted outdoors once the danger of frost has passed.

CHOOSING AND PREPARING A PLANTING SITE

• Cosmos don’t need any special soil preparation. In fact, they like soil that is not too rich, as rich soil will encourage foliage at the expense of blooms.
• Soil should be well-draining.
• Cosmos are tolerant of most soil pH levels, but grow best in neutral to alkaline soils.
• Cosmos can tolerate warm, dry weather very well. They are even drought-tolerant.
• Depending on the variety, cosmos can grow anywhere between 18 to 60 inches tall, so plan accordingly.

HOW TO PLANT COSMOS

• Just sow seeds lightly—no more than ¼-inch deep.
• Thin to 12–18 inches apart when seedlings are a few inches tall. 
• If you are growing cosmos from seeds, be mindful that it takes about 7 weeks to first bloom. After that, though, your flowers should continue to bloom until the first fall frost.
• If you let the spiky-brown seed heads blow away during the fall, cosmos are likely to self-sow throughout your garden.