Cosmos Flowers

Growing cosmo seedlings indoors

Zone 11763 | caitlinnnq10 added on April 8, 2018 | Answered

I live in New York and have no choice but to keep my cosmos inside until about may 15th when danger of frost passes. I originally had the cosmos in small seed cells, but once roots stuck out I moved them to 3 inch pots. They are growing way slower than they did in the cells and it’s been almost a week since transplant. I’m very new to gardening so what I’m really wondering is what should the next step be.. Are these seedlings going to be able to stay in 3 inch pots for long? Is it normal for there not to be much growth after transplant? Also, when they are full grown what is a practical pot height for these cosmos? Do their roots grow very deep in soil? If anyone can help I appreciate you so much. Just want to know the best way to grow these beauties.

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Answered on April 8, 2018

A sulking plant is common even a week after transplant. Cosmos are known not to like this disturbance which is why some gardens feel there is no advantage to starting them indoors. Keeping them in a cool environment with minimal fertilizer and adequate supplemental lighting will help keep them from outgrowing their 3 inch pots. Tall cosmos, over 4 ft, are not appropriate for containers and are likely to flop. All plants in containers develop deeper roots since lateral spread is contained. A 10-12 inch container for each 3-4 ft. cosmos should be enough.

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