10 Tall Annual Flowers that Make a Strong Impact

Verbena (Verbena Bodariensis)
Jacqui Hurst / Getty Images

We often think of annuals as quick filler, but there are many annual flowers that are quite tall and striking on their own. There are several annuals that are tall enough for the back of the border and bold enough to make their own statement. Although some are hard to find in the garden center, they can all be grown from seed, and since they are annuals and rushing to set their own seed, they grow quite quickly.

Here are 10 tall annuals you can consider that will make a strong statement in your garden.

  • 01 of 10

    Floss Flower (Ageratum Houstonianum)

    Ageratum houstonianum
    Marie iannotti

    Most of the ageratum plants sold in garden centers are compact, short plants with blue/purple flowers, generally used for edging garden beds. These are not the only ageratums available, although the larger varieties are sometimes pushed out of the limelight. The Ageratum houstonianum offers varieties ranging from 6 inches to 30 inches. An excellent taller cultivar is A. houstonianum 'Blue Horizon', which forms an attractive blue haze when planted in clusters. It is extremely appealing to butterflies and other pollinating insects.

    Ageratum like regular water. Allow the soil to dry between waterings, because the plants can be prone to crown and root rot. To prevent botrytis, water them in the morning to give the leaves a chance to dry off. Deadhead the spent flowers to keep the plants reblooming throughout the summer.

    • USDA Growing Zones: 2 to 11; normally grown as an annual
    • Color Variations: Blue/purple (pink and white cultivars also available)
    • Sun Exposure: Full sun to partial shade (prefers some afternoon shade to prevent burn-out)
    • Soil Needs: Moist, well-drained soil
  • 02 of 10

    Amaranth (Amaranthus Spp.)

    flowering love lies bleeding (Amaranthus caudatus)
    Justus de Cuveland / Getty Images

    Several species within the Amaranthus genus are commonly known as "amaranth" or "love-lies bleeding." An excellent tall species is A. caudatus, which can grow to 3 to 5 feet tall, with long panicles of dangling flowers. Another tall species is A. hypochondriacus (prince's feather), which grows to about 4 feet, with flowers held in upright panicles in shades of red, purple, gold, and green. Finally, there is A. tricolor, sometimes knows as "Joseph's coat" or "summer poinsetta", which has unremarkable flowers but lovely green leaves that break into a tropical part of tropic colors, from red to purple to gold.

    All the amaranths are quite easy to grow from seed; in cooler climates, start them indoors then transplant into the garden when the seedlings reach 6 inches or so.

    • USDA Growing Zones: 2 to 11; normally grown as an annual
    • Color Variations: Red
    • Sun Exposure: Full sun to part shade
    • Soil Needs: Moist, well-drained soil
  • 03 of 10

    Castor Bean (Ricinus communis)

    Castor oil plant -Ricinus communis-, fruits, Europe
    Guenter Fischer / Getty Images

    Castor bean is often avoided as a garden plant form because the seeds are extremely poisonous and the leaves can be an irritant. These plants contain ricin, a toxin that has been used as a bio-weapon, though it rarely causes death in its unrefined form. If you have young children or pets, this is not the plant for you. But if you do not have young garden visitors, castor bean provides many ornamental features.The star-shaped leaves are what draws in most gardeners. Their deep purple color alone made the plant worth growing. But they also have interesting seed pods and the newer varieties have more attractive flowers in red and pink. The plants can easily top 10 feet, and sometimes keep growing to 15 feet.

    To get the largest plants, either buy seedlings or start seeds early, 6 to 8 weeks before last frost. As with most tall growing plants, castor beans need to be allowed to grow without interruption. Keep moving them into larger pots as they fill out their old ones. Make sure they have plenty of heat and sun and harden them off gradually.

    • USDA Growing Zones: 9 to 11; normally grown as an annual
    • Color Variations: Greenish-yellow; cultivars with red flowers are also available
    • Sun Exposure: Full sun
    • Soil Needs: Rich, moist, well-drained soil
  • 04 of 10

    Spider Flower (Cleome hassleriana)

    Cleome in Bloom
    Marie Iannotti

    Cleome is a genus known collectively as spider flower, with cultivars of C. hassleriana as the most common variety sold commercially. Spider flower starts blooming early and gets better as the season rolls along. The first blooms begin when the plants are only about 1 foot tall. As the plant grows in height, more flowers form at the top of the plants. Although height depends on the variety you are growing, most can grow to 4 to 5 feet, branching along the way and producing even more flowers.

    You can direct sow cleome seeds, and the plants easily self-seed in the garden, though they may be slow to germinate. If you want earlier blooms, or to extend the season even longer, you can start seed indoors, 6 to 8 weeks before your last frost date.

    • USDA Growing Zones: 9 to 11; generally grown as an annual
    • Color Variations: White, pink, lavender, rose
    • Sun Exposure: Full sun to part shade
    • Soil Needs: Medium-moisture, well-drained soil; prefers slightly acidic pH
    Continue to 5 of 10 below.
  • 05 of 10

    Cosmos (Cosmos bipinnatus, C.sulphureus )

    Close-Up Of Pink Flower
    Paul Harsch / EyeEm / Getty Images

    Cosmos is one of the most undemanding annual flowers you can grow. You can start seed indoors to get an early start, but it is easiest to direct sow in the garden by broadcasting any time around your last frost date. There are two common species of cosmos:

    • C. bipinnatus has feathery foliage and daisy-like flowers with yellow centers. You will find them in an assortment of colors and sizes, so if you are looking for tall plants, be sure to read the seed packet. Some varieties can reach up to 4 feet in height.
    • C. sulphureus is a taller plant, growing to 6 feet, with yellow or orange flowers.

    Cosmos will repeat flower even without deadheading. However, the plants will last longer if you either deadhead or wait until flowering declines and shear back the whole plant by about half. Cosmos readily self-seed. Some gardeners find this a nuisance, but the volunteers are easy enough to pull out, while young. If you leave the plants standing through winter, you will find that birds love their seeds.

    • USDA Growing Zones: 2 to 11; normally grown as an annual
    • Color Variations: White, pink, red, yellow, orange
    • Sun Exposure: Full sun
    • Soil Needs: Medium-moisture, well-drained soil
  • 06 of 10

    Kiss Me Over the Garden Gate (Persicaria orientale)

    Persicaria orientale
    Francois De Heel / Getty Images

    There are several notable Persicaria species and some, like Persicaria polymorpha, are perennial. P. orientale, also known as "kiss me over the garden gate" or "knotweed," is a quick-growing annual type with spikes of purple-pink flowers that bloom above the foliage. (This plant is not related to the invasive Japanese knotweed.) You can direct sow or start seed indoors, 4 to 6 weeks before the last frost date. They are very quick growers and can reach 6 to 10 feet in a matter of weeks. Persicaria needs regular moisture; mulching is recommended.

    • USDA Growing Zones: 2 to 11; normally grown as an annual
    • Color Variations: Purple-pink
    • Sun Exposure: Full sun to part shade
    • Soil Needs: Medium-moisture, well-drained soil
  • 07 of 10

    Flowering Tobacco (Nicotiana sylvestris)

    Nicotiana sylvestris
    David Q. Cavagnaro / Getty Images

    Flowering tobacco is yet another stately, old-fashioned flower that has been overshadowed by shorter varieties. It can grow to 6 feet and produces a jasmine-like scent in the evenings. During the day, the flowers partially close and no scent it released, but it makes up for it at night. Because of this habit, these are great plants for a patio or deck where you spend time in the evening. Flowering tobacco is easy and quick to grow from seed. Do not cover the seed with soil, because it needs light to germinate.

    • USDA Growing Zones: 10 to 11; normally grown as an annual
    • Color Variations: Yellow-green to white, pink, red
    • Sun Exposure: Full sun to part shade
    • Soil Needs: Rich, moist, well-drained soil
  • 08 of 10

    Sunflower (Helianthu annuus)

    Teddy bear sunflowers
    Image Source / Getty Images

    Sunflowers may well be among the first flowers you think of when you go looking for tall annuals. Annual sunflowers used to be late bloomers, but new varieties that are "day-neutral," meaning they do not require long days to start setting buds—these begin blooming in mid-summer. The traditional yellow sunflowers are still popular, but now you can also find cultivars in rich burgundy, deep mahogany, and many bi-colors. The flowers can be huge, up to 1 foot in diameter.

    You can start seed indoors 2 to 4 weeks before your last frost date, but sunflowers do not like their roots disturbed, so plant them in peat or paper pots that can be planted directly into the garden. Sunflowers grow so quickly, though, that is it easy enough to sow the seeds directly into garden soil. Note that this plant self-seeds so readily that it is considered a noxious weed in parts of the Midwest.

    • USDA Growing Zones: 2 to 11; grown as annuals
    • Color Variations: Yellow with brown centers; cultivars are also available with burgundy and brown flowers
    • Sun Exposure: Full sun
    • Soil Needs: Moist, well-drained soil; tolerates poor, dry soil
    Continue to 9 of 10 below.
  • 09 of 10

    Tithonia (Tithonia rotundifolia)

    Mexican Sunflower (Tithonia)
    Marie Iannotti

    Mexican sunflower, also known as torch flower, is not a popular in gardens lately, but it's likely to make a comeback, since this cheery, bright orange flower is easy to grow and is virtually pest-free. The species typically grows to 4 to 6 feet in height, though dwarf cultivars are also available. It loves hot days and does equally well in high humidity or drought conditions.

    Tithonia takes awhile to start blooming. To speed things along, you can start seed indoors 6 to 8 weeks before the last frost. It needs some light to germinate, so press the seeds against the soil, rather than covering them.

    • USDA Growing Zones: 2 to 11; normally grown as an annual
    • Color Variations: Orange-red with yellow centers
    • Sun Exposure: Full sun
    • Soil Needs: Dry to medium-moisture soil
  • 10 of 10

    Tall Verbena (Verbena bonariensis)

    Verbena (Verbena Bodariensis)
    Jacqui Hurst / Getty Images

    Tall verbena, sometimes known as Brazilian vervain, is an unusual plant that forms a low clump of leaves, then sends up tall, bobbing stems with clusters of purple flowers. On its own, it is not a show stopper, but let it weave its way through your garden and everyone will be asking you what it is. Tall verbena can grow to 4 to 6 feet tall. It has a branching habit that you can encourage by pinching the young plants back when it is about 6 inches tall. The plants tend to self-sow throughout the garden, but the volunteers are easily removed and can be transplanted elsewhere if you wish.

    • USDA Growing Zones: 7 to 11; grown as an annual in colder climates
    • Color Variations: Rose, violet
    • Sun Exposure: Full sun to part shade
    • Soil Needs: Moist, well-drained soil