The 7 Best Fast-Growing Flowers to Plant in July for a Stunning Fall Garden

A Guide to Fast-Growing Annuals for Late Summer Planting

From watering and weeding to entertaining family and friends over a summer barbecue, July can be a busy time in the garden. Nevertheless, if you find yourself wanting to fill some gaps in the borders or empty spaces in your containers before the fall, there is still time to sow some fast-growing annuals for autumnal color.

Often germinating in just a few days and blooming within a matter of weeks, fast-growing annuals can be a cost-effective and efficient way of filling any gaps at this time of year. Over my nearly two decades of professional horticultural experience, I have discovered which annual flowers can be planted now and still have time to bloom before winter sets in.

Furthermore, it is not just flowers you can plant in July; there is still time to sow salads and vegetables this month for harvest later this season. Here are seven of the best options to consider:

Ornamental Cabbage

Also known as ornamental or flowering kale, ornamental cabbage (Brassica oleracea) may resemble its edible relatives but is grown for its striking color and form rather than for food. Perfect for a fall and winter garden, ornamental cabbages are available in shades ranging from cream and pink to blue and purple.

Germinating in around one week in soil with a temperature of 65°F – 70°F, ornamental cabbages can reach maturity in 60-90 days, meaning if sown in July, you could be enjoying their vibrant hues come September.

Ideally suited to a fall planter or the front of a border and available in pink, white, or a mix, Flowering cabbage – Osaka series are available from True Leaf market.

Dwarf Cosmos

Instantly brightening borders, adored by pollinators and florists, it is no surprise that cosmos are a widely grown annual flower.

Typically started in late spring or early summer, you can also sow cosmos in July. However, in order to mature before the winter sets in, you might want to choose a faster-growing dwarf variety such as Cosmos ‘Dwarf Sensation’ available from True Leaf Market rather than the taller Cosmos bipinnatus.

Germinating in as little as one week and flowering in 60-90 days, dwarf cosmos is a great choice for later-season sowing. Sow indoors or outdoors at a depth of a quarter of an inch, water in gently and protect from slugs and snails.

To avoid dispersing seed when watering, a watering can with a fine rose or a gentle setting on a hose spray gun is recommended. The Haws Bartley Burbler watering can with fine spray rose is available to purchase from Amazon.

Amaranth

Grown for cut flowers, as a crop, and as a microgreen, the Amaranthus plant group is made up of both annuals and perennials. However, Love-lies-bleeding, or Amaranthus caudatus, that is prized for its cascading flowers.

Amaranth matures quickly and thrives in the heat; it dies back with the first frost of winter, which makes later sowings possible for those with a mild fall. Maturing in about 10-12 weeks, you will want to sow it as early in July as you can to allow it time to bloom.

Requiring light to germinate, make sure they have contact with the soil, but do not cover. Sow in cell trays and place in a propagator or heat mat, such as the VIVOSUN heat mat with digital thermostat available from Amazon, set to 65°F to 75°F until seedlings appear then pot on as they grow.

Plant out in full sun and keep the soil moist. Love lies bleeding seeds are available to purchase from Amazon.

Dill

Botanically known as Anethum graveolens, florist’s dill is so called due to its use as a cut flower. It produces fine and feathery foliage upon which grew elegant clusters of tiny yellow flowers.

Low maintenance and drought tolerance make dill an easy-to-grow annual to sow in July. You can sow it directly outdoors into a prepared seedbed that receives full sun, or sparingly in a pot under cover. Cover the seeds very thinly with soil and keep moist until germination occurs, usually within 10 days.

With experience of growing it as a cut flower commercially, florist’s dill tends to flower more quickly when given as much sun and heat as possible, making a July sowing ideal in warmer areas.

Maturing in 65 days, you can purchase dill seeds – ‘Bouquet’ from True Leaf Market.

French Marigolds

Cultivated for their vibrant orange, red, and yellow flowers, French marigolds (Tagetes patula) are a great addition to a vegetable patch for their natural pest-controlling characteristics.

Whether planted in a container, front of a border, or in a greenhouse, Tagetes keep blooming all summer long until the first frost of the fall. Adding some warm color to a hot border or a fall display, French Marigolds are easy to grow and care for.

Faster-growing than African marigolds, Tagetes can be sown outdoors or undercover in July and tends to germinate within 1-2 weeks. Blooming in as little as 50 days, if sown in early July, you could be enjoying its striking blooms before the end of August.

Developing maroon and yellow flowers, Naughty Marietta French marigold seeds are available to purchase from Botanical Interests.

Cornflowers

Perfect for a wildflower garden, cornflowers, or bachelor’s buttons are among the most stunning blue flowers to grow.

Typically planted in the spring, you can also sow Centaurea cynus in July, albeit with a shorter flowering season. Thriving in full sun and poor soil, sow them where they are to grow, and, in the right conditions, they will bloom within 10 weeks from sowing.

Alternatively, you can sow them in a pot using a seed mix such as Miracle-Gro Seed Starter Potting Mix available at Walmart. For a change from the commonly grown blue cornflowers, why not try ‘Black Magic’ bachelor’s button Seeds available from Botanical Interests, for its striking and unusual deep maroon flowers.

Baby’s Breath

One of the best fast-growing plants with tiny flowers is baby’s breath (Gypsophila). Adored for its panicles of minute white or sometimes pink flowers, Gypsophila adds a delicate and airy feel to any pot or border.

Furthermore, as a quick-maturing annual, it can bloom in as little as 50 to 60 days from sowing.

With a dislike of being transplanted, direct sowing is generally preferred, and needing light to germinate, should not be covered with soil, but merely pressed gently into damp soil. Once germinated, thin plants to 12-18 inches apart and avoid fertilizing, as this can lead to more leafy growth and fewer flowers.

With its delicate pink blooms, Gypsophila ‘Gypsy Deep Rose’ seeds are available to buy from True Leaf Market.

With all this talk about fall color, you may be thinking about what you can sow in the fall for an early spring display next year. From hardy annuals to perennial options, our best flowers to sow in the fall are full of varieties you can sow for healthier and stronger plants and an earlier display next year.