Help Cosmos Flowers Thrive In Garden Containers With A Simple Gardening Tip

If you're looking for cheery, colorful annuals with a reputation for being quick and easy to grow for beginner gardeners, look no further than cosmos flowers (Cosmos spp.) In fact, the standard gardening advice for growing cosmos is to avoid over-watering or over-fertilizing these flowers. The Mexico natives are prone to mildew or stem rot if overwatered and may produce fewer blooms if over-fertilized. This is actually what makes them such a great low-maintenance addition to your flower beds. These annuals will flower from spring through summer when planted in dry, nutrient-poor soil that's allowed to dry out between watering.

However, growing these daisy-like flowers in containers requires a little more care than the average hardy plant would need if you were growing it in the ground. The soil in containers tends to leach nutrients and, depending on the mix you use, lose moisture faster than it would in the ground. So even a poor, dry, soil-loving plant like cosmos flowers benefits from a light application of fertilizer and more careful watering when growing in a container. While a little more effort is needed to take care of cosmos plants growing in a container, it's still possible to overdo it. So, make sure to feed your cosmos sparingly and water them only when the soil has dried out.

The easy-to-grow cosmos flower can become a little more finicky in a container. Too much fertilizer can result in a leafy plant with few blooms. Too little fertilizer and the container soil might become too nutrient-poor even for the minimal nutrient requirements of these hardy flowers. To start, choose potting soil that doesn't already have fertilizer or compost mixed in. Instead, prioritize a mix with good drainage and add fertilizer yourself so you can adjust the amount to suit your flowers' needs.

To compensate for nutrient loss in containers without over-fertilizing your cosmos flowers, opt for a slow-release fertilizer, like Jobe's Organics Slow Release Plant Food, so the plant doesn't get a hefty dose of nutrients all at once. It also helps to dilute the fertilizer or apply about half the recommended amount. Add this to the potting soil at the start of the season. You can apply another diluted dose in summer or, if growing from seed, just before the first buds appear. But don't fertilize more than once or twice in a growing season. 

Since frequent watering is part of the reason container soil leaches nutrients so quickly, it's also important to avoid over-watering. The soil should be kept moist while seeds germinate and cut back once you see the seedlings pop up. From then on, water your cosmos sparingly and allow the soil to dry out in between watering. This will reduce the risk of disease while minimizing the amount of fertilizer that drains out of your pot.