Do Self-Seeding Cosmos Come Up Every Year?

Too Much Fertilizer

• Cosmos prefer poor soils and will actually grow better in ground that has not been amended. If you add extra fertilizer to an area where you grow cosmos, they will be less likely to bloom. Without blooms, you won't have seeds. Cosmos should be grown away from plants that require frequent feedings such as roses or vegetables. Instead, grow them along with plants with similar needs such as California poppy or chicory.

Too Little Sun

• Cosmos require at least six hours of full sun every day while they are growing. Without this much sun, the plants will grow lanky and fail to bloom. Cosmos that don't bloom won't be able to go to seed. When you first plant cosmos, make sure trees or buildings don't shade the area.

Too Much Water

• This is a problem you may not be able to avoid. Cosmos drop their seeds to the ground where they wait for conditions to be right to sprout. If the soil the seeds lie in stays soggy for long periods of time, the seeds will rot. To lessen the likelihood of this problem, work sand into the area where cosmos grow. This improves water drainage and loosens the soil.

Temperature Changes

• Your cosmos will germinate in the spring once the temperatures start to warm. If a cold snap hits your area after the seedlings emerge, the frost can damage the seedlings to the point that they won't recover. The only solution to this is to place a heavy sheet or thin blanket over your cosmos seedlings if freezing temperatures are predicted.

Birds

• Birds love cosmos seeds. It is unlikely they will be able to eat all the thousands of seeds from a healthy cluster of cosmos. However, if your plants only produce a few blooms, it is possible that birds could gobble up all the seeds. To ensure your cosmos bursts with blooms, keep them in full sun, don't fertilize them and never overwater them.