Tips for Growing Cosmos

This is the time of year when I’m getting incredibly anxious to just start gardening already! Especially since the other day I heard hundreds of geese returning (3 o’clock in the morning and they’re flying over our home honking their little heads off), and our neighborhood suddenly filled with robins, and you know how they are: it’s singsingsing all the live-long day. It’s almost time to start seeds, almost time to prune the roses, almost time to clean up the garden and almost time to plant early annuals. But not quite. So, I’m twiddling my thumbs, staring out of the window a lot, and gleaning some garden photos to gaze at, like these of our cosmos from last summer.

Cosmos make excellent cut flowers!  (seen here with sunflowers and ‘Knock Out’ roses)

Cosmos Growing Tips:

In my experience, cosmos doesn’t do as well if the soil is too rich which is good news because who has perfect soil in their entire garden? Well, maybe Martha Stewart does, but I know I sure don’t. (Rich soils will only cause the plant to grow tall and lanky and take forever to bloom.) Also, while I’ve read that cosmos doesn’t transplant well, I still start mine in little pots, such as these, sometime in late April or beginning of May, and that way I can just plant the pot and all and not worry about transplant shock or thinning seedlings, which is one of my least favorite gardening chores.

Cosmos prefers sun, but I’ve had success planting them in a shadier area of our yard and still had lots of blooms. Those plants received about 4 hours of mid to late afternoon direct sun. (Of course, the cosmos growing in full sun bloomed even more.) I also like to plant some cosmos as the center plant in a container with trailing annuals around it. Just again, watch that the soil isn’t too heavily amended and rich or it will simply shoot up like a rocket and put out lots of leaves and not flowers.

Cosmos doesn’t like wet feet and is pretty drought tolerant. I rarely water them during the summer relying on the rain to take care of that. Among annuals, it’s lovely combined with zinnias. It also makes a fine companion to those old standby perennials such as coneflowers. They will grow from mid summer all the way until frost. (In fact, most of these photos were taken in mid-late October.)

Cosmos will attract a myriad of butterflies and is also self-sowing so don’t be surprised if more pop up in odd places the following year. It truly is one of the easiest and most rewarding annuals to grow and nowadays there are lots of varieties to choose from. Want more info? This is a great site about cosmos. Need seeds? Try Renee’s Garden for a fantastic selection.


3 thoughts on “Tips for Growing Cosmos

  1. I have to buy my cosmos from garden centre. Only have patio garden and no room to grow from seed. When should I buy plants to put in pots Having garden party first week of July and would like them to be at best. .What is the best type of compost to use. Going on holiday end of May for one week.
    Would appreciate any advise on how to keep after blooming usually just throw away as need pots to grow bulbs.
    Look forward to your advise

    1. Hi there! Whenever I purchase my annuals from a garden center, especially ones that don’t like any kind of frost, I wait until the last possible frost date for my zone. (If you’re not sure what your climate zone is, here is a link for that.) As cosmos do not flower well if the soil is too rich, regular potting soil should work fine. Pinch the young plants to encourage branching and keep cutting the flowers to encourage re-bloom. Hope this helps!

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