Cosmos Not Flowering: Why Are My Cosmos Not Blooming

Pink Cosmos Flowers
(Image credit: Sundaemorning)

Cosmos is a showy annual plant that is part of the Compositae family. Two annual species, Cosmos sulphureus and Cosmos bipinnatus, are the ones most commonly seen in the home garden. The two species have different leaf color and flower structure. The leaves of the C. sulphureus are long, with narrow lobes. The flowers from this species are always yellow, orange, or red. The C. bipinnatus has finely cut leaves that resemble pieces of thread. The foliage is quite fernlike. Flowers of this type are white, rose, or pink. What happens though when there are no blooms on cosmos? Keep reading to learn more.

Why are My Cosmos Not Blooming?

Cosmos are fairly easy to grow and generally quite hardy, although some gardeners report that their cosmos did not bloom as expected. Below are the most common reasons for non-blooming in cosmos plants.


Sometimes we get a little overzealous for plant bloom but forget that it takes about seven weeks for cosmos to come into bloom from seed. If you have no blooms on your cosmos, it may be that they are not mature enough to produce bloom. Check the tips to see if they are starting to produce buds before getting too worried.

Over Fertilization

Another reason why cosmos may be reluctant to bloom may be because the plants are getting too much nitrogen fertilizer. Although nitrogen is a necessary nutrient for healthy green growth, too much can be a bad thing for many plants. If your cosmos plant will not flower but has produced a lot of healthy looking leaves, it may be due to overfertilization. If you are presently using a 20-20-20 fertilizer, with 20% nitrogen, phosphorous, and potassium, try switching to a type with less nitrogen. Generally, fertilizers with names such as “More Bloom” or “Bloom Booster” are made with much less nitrogen and more phosphorus to support healthy blooms. Bone meal is also a good way to encourage flowering. It may also be wise to add fertilizer only at the time of planting. If you provide organic compost, most cosmos will do quite well in this fashion. You could give your plants a boost once a month with a non-chemical fertilizer, like fish emulsion with a 5-10-10 formula.

Other Concerns

Cosmos not flowering can also be due to planting old seeds. Be sure that you plant seeds that have not been in storage for longer than a year. In addition, cosmos will not tolerate long periods of cold and wet weather, as they actually prefer it dry. Be patient though, they should still bloom, just later than usual.