How Deep to Plant Cosmos Seeds: A Growers Guide

Cosmos are one of the most reliable flowering annuals around, thriving in a single growing season and giving you plenty of colorful blooms come summertime. If you’re planning on growing them, then you should know how deep to plant cosmos seeds.

Beginners of cosmos plants will have nothing to worry about, as cosmos seeds typically germinate quickly even if you put them too deep. That said, the right depth at which to plant cosmos seeds is half an inch into the soil, quickly followed by a thorough soaking to activate their growth.

How Do I Plant Cosmos Seeds?

how deep to plant cosmos seeds

You can start cosmos as soon as spring rolls around and when all the danger of frost has passed. Cosmos seeds can be sown outside directly into the ground, or in containers or seed starting trays about four weeks before the last frost date in your region.

Cosmos are tough and hardy plant specimens, and they do not require any soil preparation at all. You can use a sterile soil medium that’s been reused for growing cosmos, and the plants will still thrive. Make sure it drains well and doesn’t collect too much water or moisture.

Cosmos seeds are about an inch long and very thin. To sow cosmos seeds, you should dig up around half an inch of soil, place them in and cover the top lightly with the same medium. Observe a space of 8 inches in-between for smaller varieties and about 10 to 12 inches for the larger types. Water them in well and remember to spray to keep the soil constantly moist. In about 5-7 days the seedlings should emerge.

The planting site is just as important for the cosmos. If you want lots and lots of daisy-like blooms, put them in an area that gets plenty of sunlight. The more direct sun you can give, the better. Cosmos only want one thing, and that’s light, even if the soil is poor and you don’t water them regularly.

Can Cosmos Be Planted Deep?

how deep to plant cosmos seeds

Cosmos seeds do not need a lot of soil contact to germinate. You can sow the seeds no more than half an inch deep, or a fourth of an inch if possible. Any deeper and you run the risk of the seed trying to reach for the light and expending all of its energy in the process.

You can sow two or three in a spot and thin them out a week after they germinate. Curiously enough, you can sprinkle the cosmos seeds on the ground, then sprinkle some dirt or garden soil on top and spray with water. Watch out for the seedlings and bring them outdoors if in trays or containers so they can get essential sunlight.

The best temperature range to germinate cosmos is around 60 to 75 degrees F, and the best temperature for growing cosmos plants is above 50 degrees F. When transplanting, it’s generally okay to plant cosmos deeper if they get too leggy.

Cosmos can be grown in containers and garden beds provided that they’re in the right depth. There are a lot of options you can choose to plant with cosmos.  You can start them in a seed tray, then move to a 12-inch container with a wide base once the seedlings have three sets of true leaves or are around 6 to 8 inches in height. Move the pots to a sunny spot to continue optimal growth and flowering.