7 Fast-Growing Flowers You Can Sow in Summer

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Sulphur cosmos

“What flowers can you still plant from seed?” At a talk I gave last weekend on flower gardening at my local library, that was the most-asked question. In response, here are seven easy-to-grow flowers you can sow in summer for great color from late summer til frost. Best of all, you will have healthy young plants coming along when spring flowers begin to fail.

Filling autumn with flowers may be easier than you think. Rather than twiddling with seed starting mix and containers, you have the option of direct-sowing seeds, or growing seedlings in a cushy nursery bed. Direct-sown seeds germinate quickly when planted in warm soil that is kept constantly moist. Plan to use a shade cover to maintain good germination conditions.

The seven flowers listed below, in alphabetical order, germinate quickly and make rapid new growth, two essential talents for summer-sown flowers. When grown in a nursery bed, seedlings can be carefully lifted and transplanted during a period of cloudy weather. Why wait? For the cost of a few seeds, you can infuse fresh colour into every corner of the garden during summer’s second half.

Garden balsam thrives in partial shade

Shade-Loving Garden Balsam

Garden balsam (Impatiens balsamina) is also known as touch-me-not, because the ripe seed pods explode at the slightest touch. Two hundred years ago, it was hugely popular as a tropical flower anyone could grow. The only flower on this list that adapts well to shade, garden balsam often naturalises in hospitable spots. Native to India, garden balsam thrives in humid heat, and starts blooming in a few short weeks.

Direct-sown calendulas are lush enough to work as an end-season cover crop

Calendula for Covering the Ground

Calendula can go from seed to bloom in only six weeks, so it is a perfect fit for spaces in need of an autumn facelift. Sow seeds outdoors in a shady spot in July, and start moving them into beds and containers after summer’s heat has peaked. Autumn-grown calendulas produce a lush cover of leaves, so I have even used them as a weed-choking cover crop in the vegetable garden.

Fast and easy sulphur cosmos produces a bumper crop of seeds

Please Bees and Butterflies With Sulphur Cosmos

Sulphur cosmos are the easiest flowers to sow and grow in the summer garden. Blooming in shades of yellow and orange, sulphur cosmos prospers in heat that causes regular cosmos to melt down with disease. Direct sow seeds in early June, just before rain is expected, and you will see seedlings within a week. Extra seedlings are easy to lift and transplant. Bees and butterflies often visit sulphur cosmos blooms, and then the plants produce seeds that are easy to gather and save for replanting in subsequent seasons.

Marigolds are a beautiful way to rehabilitate soil where diseases are present

Marigolds to Improve Soil

Marigolds should never be underestimated as a source of fabulous autumn colour. Summer-sown plants of small-flowered dwarf French marigolds (Tagetes patula) in shades of orange, yellow and mahogany often hold back until nights lengthen in late summer, and then burst into bloom as leaves begin to fall. The roots of this species help stimulate the soil food web while starving out problem nematodes, so French marigolds also can be considered a healing plant for troubled sections of the garden.

Summer-sown nasturtiums continue to grow until freezing weather arrives

Autumn Salads With Nasturtiums

Nasturtiums that grow from seeds shed in the garden the previous season often do not appear until early summer, because nasturtiums germinate best in warm soil. However, the plants suffer in high heat, so wait until late July to sow seeds for autumn blooming. Grow summer nasturtiums in lean soil to keep them from growing scads of leaves rather than flowers. Nasturtium leaves and flowers that grow in cool autumn weather are tasty additions to salads.

Summer-planted sunflowers may not reach the same heights as spring-sown ones, but they will bloom vigorously

Short but Sweet Sunflowers

Sunflowers can be phenomenally successful in late summer, with one caveat: The display must face south. In any season sunflowers are likely to twist so they face the setting sun, but as late summer sun become weaker and days shorter, sunflowers become even more resolute about following the sun. Summer-planted sunflowers will start blooming in about eight weeks, on plants that may be shorter than the same varieties grown in spring.

Disease-resistant narrow-leaf zinnias are late summer stars

Insect-attracting Zinnia

Zinnias planted in spring often decline in late summer due to old age and powdery mildew, so I always start more seeds in June as late summer replacements. I start seeds in small containers, outdoors in the shade, so the plants will be easy to transplant to where they are most needed. Small-flowered narrow-leaf zinnias are especially good for this use because they resist disease and need less water than large-flowered zinnias. Bees and butterflies love them, including migrating monarchs that pass through where I live in late September. The monarch migration is the last big event in my flower gardening season, staged with substantial support from summer-sown flowers.

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