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6ft tall weed with spiky seed pod

20 Tall Flowers That Make a Strong Impact

There are several annual and perennial flowers that are tall enough for the back of a garden bed and bold enough to make their own statement. Tall flowers help to add structure and depth to a garden bed. They also can be used as a living privacy fence or to hide an unattractive backdrop. Plus, because they’re so large you’ll be able to see them from afar, as opposed to small flowering plants that you can only appreciate up close.

Here are 20 tall flowers that will make a strong statement in your garden.

Floss Flower (Ageratum houstonianum)

The Spruce / Marie Iannotti

Floss flowers can reach around 2.5 feet high with a 6- to 18-inch spread. They produce clusters of fluffy blooms from June all the way until frost. These plants are easy to grow as long as they have even soil moisture with good drainage. Deadheading (removing the spent blooms) is not necessary for continued blooming, but it will make for a tidier appearance. Frost will quickly kill the plants in the fall. In addition, extremely hot summer weather might limit blooming.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: Blue-purple, pink, red, white, bicolors
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Average, moist, well-drained

Amaranth (Amaranthus spp.)

The Spruce / K. Dave

Several species within the Amaranthus genus are commonly known as amaranth or love lies bleeding. An excellent tall flower species is A. caudatus, which can grow to 3 to 5 feet with long panicles of dangling blooms. Another tall species is A. hypochondriacus, which grows to around 4 feet with flowers held in upright panicles in shades of red, purple, gold, and green. All the amaranths are easy to grow from seed. However, they are susceptible to many common garden pests.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: Red, pink, purple, yellow, orange, green
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Average, moist, well-drained

Castor Bean (Ricinus communis)

The Spruce / Evgeniya Vlasova

Castor bean plants are tall flowers that can reach around 6 to 10 feet high with a 2- to 4-foot spread. They grow quickly with glossy green foliage. In the summer and fall they bloom with somewhat insignificant flower spikes. It’s the reddish-brown seed capsules that have the real ornamental value. While this plant provides lots of visual interest to the garden, all parts of it are toxic when ingested to people and animals. So be sure to plant it away from areas with children and pets. Also, situate it somewhere that's protected from strong winds.

  • USDA Growing Zones: 9 to 11
  • Color Variations: Green-yellow, red
  • Sun Exposure: Full sun
  • Soil Needs: Rich, moist, well-drained

Spider Flower (Cleome hassleriana)

The Spruce / Marie Iannotti

Spider flowers start blooming early and get better as the season rolls along. The first blooms begin when the plants are only about 1 foot tall. As the plants grow, more flowers form at the top. Although height depends on the variety you are growing, most can reach 4 to 5 feet, branching along the way and producing even more flowers. You can direct sow seeds, and the plants easily self-seed in the garden. However, that means if you don’t want them to spread you’ll have to keep pulling seedlings as they pop up.

  • USDA Growing Zones: 10 to 11
  • Color Variations: White, pink, lavender
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Slightly acidic, medium moisture, well-drained

Cosmos (Cosmos sulphureus, Cosmos bipinnatus)

The Spruce / Leticia Almeida

Cosmos is one of the most undemanding tall flowers you can grow. There are two common species of cosmos. C. bipinnatus has feathery foliage and daisy-like flowers with yellow centers, and some varieties reach up to 4 feet tall. C. sulphureus is a taller plant, growing to around 6 feet with yellow or orange flowers. Cosmos will repeat flower from summer to fall 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.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: White, pink, red, yellow, orange
  • Sun Exposure: Full sun
  • Soil Needs: Medium moisture, well-drained

Kiss-Me-Over-the-Garden Gate (Persicaria orientale)

The Spruce / Evgeniya Vlasova

Persicaria orientale, commonly known as kiss-me-over-the-garden gate or knotweed, is a quick-growing annual with spikes of purple-pink flowers that bloom from summer to fall above the foliage. The plant reaches around 4 to 7 feet high with a 2- to 4-foot spread. It will attract hummingbirds and other pollinators to your garden. But strong winds can damage it, so it must be in a protected site. Mulching is recommended to retain soil moisture.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: Purple-pink
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Medium moisture, well-drained

Flowering Tobacco (Nicotiana sylvestris)

The Spruce / Autumn Wood

Flowering tobacco is a stately tall flower with its clusters of trumpet-shaped blooms. It can grow to around 5 feet and produces a jasmine-like scent in the evenings. During the day, the flowers partially close, and no scent it released. Because of this habit, these are great plants for a patio or deck where you spend time in the evening. However, they should not be grown near tomatoes or other members of the nightshade family, as they all are susceptible to some of the same plant viruses.

  • USDA Growing Zones: 10 to 11
  • Color Variations: White, yellow-green, pink, red
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Rich, moist, well-drained

Sunflower (Helianthus annuus)

The Spruce / Ana Cadena

Annual sunflowers bloom in the summertime with their broad flowers on upright stalks. Gardeners have several options when it comes to these annuals. The traditional yellow sunflowers are still popular, but now you can also find cultivars in rich burgundy, deep mahogany, and many bicolors. They grow between roughly 3 and 10 feet high. And they don't require much care, though you can remove depreciated foliage for a tidier appearance. Birds love to feed on the seed heads. However, note that this plant self-seeds so readily that it is considered a noxious weed in some areas.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: Yellow, red, brown
  • Sun Exposure: Full sun
  • Soil Needs: Average, moist, well-drained

Mexican Sunflower (Tithonia rotundifolia)

The Spruce / Marie Iannotti

Mexican sunflowers are easy to grow and virtually pest-free. The species typically grows to around 4 to 6 feet tall, though dwarf cultivars are also available. These tall flowers love hot days and do equally well in high humidity or drought conditions. However, they can take a while to start blooming. To speed things along, start seeds indoors six to eight weeks before your area's last projected frost date in the spring.

  • USDA Growing Zones: 2 to 11 (annual)
  • Color Variations: Orange-red with yellow center
  • Sun Exposure: Full sun
  • Soil Needs: Average, dry to medium moisture, well-drained

Tall Verbena (Verbena bonariensis)

The Spruce / Kara Riley

Tall verbena, sometimes known as Brazilian vervain, is an unusual plant that forms a low clump of leaves and then sends up tall, bobbing stems with clusters of flowers. It can grow to around 4 feet tall and blooms from summer to fall. The plant is excellent at attracting butterflies to the garden, and it can tolerate many soil types as long as there is good drainage. The plant tends to self-seed throughout the garden, so you must be on top of removing seedlings if you want to limit its spread.

  • USDA Growing Zones: 7 to 11
  • Color Variations: Pink-purple, lavender
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Average, moist, well-drained

Hardy Hibiscus (Hibiscus moscheutos)

The Spruce / Leticia Almeida

Hardy hibiscus, also known as swamp mallow, is a shrub-like perennial that’s native to wet soils, such as river banks. In the summertime, it blooms with showy flowers that have five overlapping petals. And it grows to around 3 to 7 feet high with a 2- to 4-foot spread. This plant tolerates heat and humidity quite well and can be used in a rain garden. It’s important never to let its soil dry out and to protect it from strong winds.

  • USDA Growing Zones: 5 to 9
  • Color Variations: White, pink
  • Sun Exposure: Full sun
  • Soil Needs: Rich, moist

Joe Pye Weed (Eutrochium purpureum)

The Spruce / Adrienne Legault

The tall flowers of Joe Pye weed arrive in the summertime and persist through early fall. The tiny blooms come in attractive clusters and have a pleasant vanilla scent. They’re known for attracting butterflies to the garden. This plant can reach around 5 to 7 feet tall and is easy to care for. Just make sure the soil doesn't dry out, or the leaves can scorch. Joe Pye weed looks best if you have the space to group several plants for more ornamental impact.

  • USDA Growing Zones: 4 to 9
  • Color Variations: Pink
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Rich, moist

Hollyhock Mallow (Malva alcea)

The Spruce / Evgeniya Vlasova

Hollyhock mallow grows to around 2 to 4 feet tall with a spread of less than 2 feet. It features five-petal flowers that stretch around 2 inches across and bloom in the summer to early fall. Butterflies love the flowers. To promote more blooming, remove the spent flower spikes. While it brings lots of ornamental value, this perennial does tend to be short-lived. But it can self-seed fairly well to produce new plants.

  • USDA Growing Zones: 4 to 7
  • Color Variations: Pink
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Medium moisture, well-drained

Delphinium (Delphinium spp.)

The Spruce / Autumn Wood

Delphinium, also known as larkspur, is a large genus of flowering plants that come in varying sizes. The Pacific Hybrid group includes tall flowers that grow to around 4 to 8 feet high. The flowers bloom in the summer clustered together on columnar flower spikes. While these plants offer lots of visual interest in the garden, they are fairly high-maintenance. They usually need staking to keep them upright, along with deadheading and pruning of spent growth.

  • USDA Growing Zones: 3 to 7
  • Color Variations: Blue, violet, pink, white
  • Sun Exposure: Full sun
  • Soil Needs: Rich, medium moisture, well-drained

Canna (Canna spp.)

The Spruce / Adrienne Legault

The Canna genus includes tropical and subtropical plants with showy flowers. On average, they grow between 1.5 and 8 feet tall, though exact height depends on the variety. The flower spikes rise above the foliage during the summer. These plants add rich, warm colors to the garden. But they have poor cold tolerance and must be brought indoors if the temperature nears 40 degrees Fahrenheit.

  • USDA Growing Zones: 7 to 10
  • Color Variations: Red, orange, yellow, pink, white, bicolors
  • Sun Exposure: Full sun
  • Soil Needs: Rich, moist, well-drained

Elecampane (Inula helenium)

The Spruce / Evgeniya Vlasova

Elecampane is a flowering perennial that’s part of the aster family. Its blooms have a sunflower-like appearance but with very thin petals. The flowers stretch around 2 to 3 inches across and appear from mid-summer to early fall. The plant overall can reach around 3 to 6 feet high. It’s tolerant of a variety of soil conditions. But it might need staking if it gets too tall.

  • USDA Growing Zones: 3 to 7
  • Color Variations: Yellow
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Moist, well-drained

Red Hot Poker (Kniphofia uvaria)

The Spruce / Evgeniya Vlasova

Red hot poker, also known as torch lily, provides unique visual interest to the garden. Its small, tubular flowers arise on spikes above the blue-green basal foliage in the late spring to early summer. They start out red but mature to yellow. The plant itself grows to around 3 to 4 feet high with a slightly smaller spread. Red hot poker is fairly easy to maintain. But it’s important to watch out for poor drainage, as soggy soil can kill it.

  • USDA Growing Zones: 5 to 9
  • Color Variations: Red/yellow
  • Sun Exposure: Full sun
  • Soil Needs: Average, medium moisture, well-drained

Monkshood (Aconitum napellus)

The Spruce / Autumn Wood

Monkshood has an upright growth habit, reaching around 2 to 4 feet tall with a 1- to 1.5-foot spread. Clusters of small, hooded blooms arise in the summer above the dark green foliage. This plant needs moist but not soggy soil, and its soil also never should dry out. It doesn’t have any serious issues with pests or diseases. However, all parts of the plant are toxic via ingestion and skin contact, so take care when working with it.

  • USDA Growing Zones: 3 to 7
  • Color Variations: Blue-purple
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Rich, moist, well-drained

Foxglove (Digitalis purpurea)

The Spruce / Evgeniya Vlasova

Foxglove generally reaches around 2 to 4 feet tall, though it occasionally can hit 5 feet. The flower spikes arise from a rosette of foliage at the plant’s base in the late spring. Several long, tubular blooms are grouped on the spikes, which attract hummingbirds to the garden. This perennial is short-lived and won’t produce flowers until its second year. It also can look a bit ragged by the late summer. Thus, many gardeners remove their foxglove plants after they’ve flowered and released their seeds for new plants.

  • USDA Growing Zones: 4 to 8
  • Color Variations: Pink, purple, white
  • Sun Exposure: Full sun to part shade
  • Soil Needs: Average, medium moisture, well-drained

Sneezeweed (Helenium autumnale)

The Spruce / Adrienne Legault

Sneezeweed is a clump-forming plant that grows to around 3 to 5 feet high with a spread of 2 to 3 feet. In the late summer, it blooms with daisy-like flowers that stretch roughly 2 inches across. They can persist until frost in the fall, bringing interest to the garden at a time when many other plants have finished blooming for the season. This plant does require some pruning maintenance, including deadheading to promote further blooming. Once flowering is done for the season, cut back your sneezeweed by half.

Invasive Plants

Nonnative species are also referred to as introduced, exotic, or alien species. The National Park Service defines nonnative as species that occur in a given place as a result of direct, indirect, deliberate, or accidental actions by humans. Plant species that are brought into an area as food, fiber, or ornamental landscape plantings can “jump the fence” and become established in the wild. In extreme cases, invasive nonnative species can displace native species, thereby degrading the integrity and diversity of native communities.

Purple Loosestrife

Purple loosestrife (Lythrum salicaria) appears to be a pretty flower but is actually an invasive European weed that thrives in wetlands. It was introduced in the 1800s to the northeastern United States as an ornamental flower. This perennial weed, 1-2 meters tall, chokes out native plants and forms dense stands that are unsuitable as cover, food or nesting sites for most native wetland animals.

Long flower spikes turn infested wetlands into a sea of purple during July and August, but this beauty is deceptive. The display of color scatters wetlands with enormous quantities of tiny seeds that remain viable for years.

Eradicating an established stand is difficult because of an enormous number of seeds in the soil. One mature plant can disperse 2 million seeds annually. The plant is able to resprout from roots and from broken stems that fall to the ground or into the water.

One area within the park where purple loosestrife can easily be seen is to the immediate west of Nebraska Highway 14 along Verdigre Creek between Niobrara and Verdigre.

Purple loosestrife can be managed by chemical and manual removal but lately many conservationists have been using a biological control approach. Three insect species from Europe—a weevil and two beetles—have been introduced to control this exotic weed. So far, results have been promising.

Salt cedar / Tamarisk

Most salt cedars, or tamarisks, (Tamarix aphylla) are deciduous shrubs or small trees growing to 12-15 feet in height and forming dense thickets. They are characterized by slender branches and gray-green foliage. The bark of young branches is smooth and reddish-brown. As the plants age, the bark becomes brownish-purple, ridged and furrowed. These alien plants were introduced to the western U.S. in the early 1800s as ornamental shrubs, and were planted extensively in the 1930s for erosion control.

Salt cedars are a fire-adapted species and have long tap roots that allow them to intercept deep water tables and interfere with natural aquatic systems. A mature plant can consume up to 200 gallons of water per day, and its fallen leaves add salt to the surface soil. Both of these effects can be detrimental to native species.

Its aggressive growth and ability to survive fires, droughts, flooding, cold temperatures and cutting makes this plant difficult to eradicate. A variety of methods have been used in the management of salt cedar, including mechanical, chemical and biological, with the most effective management being a combination of the three. The National Park Service treats and eradicates salt cedars as soon as they are discovered within the park.

Leafy Spurge (Euphorbia estula)

Leafy Spurge

Leafy spurge (Euphorbia esula) is a creeping perennial that reproduces from seed and vegetative root buds. Accidentally introduced in the early 1800s from Eurasia, this noxious weed, from 1 to 3 feet tall, can be found in prairies, pastures and roadsides.

Leafy spurge is taking over prairies and pastures throughout most of the Missouri River Basin. It has depleted many native species by usurping nutrients, shading native plants, and producing its own toxins. The plant is not eaten by cattle except when all other forage is absent; in these cases, digestive distress or even death has been reported. Contact with the milky sap can cause temporary blindness. Sheep and goats will eat spurge with no ill effects and can even develop a preference for it.

Leafy Spurge is capable of reproducing quickly; it has small clusters of yellow flowers along a smooth vertical stem. It is difficult to control due to its extensive root system, 15 to 25 feet deep. The root system has vast nutrient stores that enable it to recover from almost any control effort. Managing leafy spurge is best done using a combination of control methods over a period of years. Biological methods like root-boring beetles and grazing sheep can deter spurge although not as fast as herbicides. Several types of herbicides can be sprayed for spurge.

Canada Thistle

Canada thistle (Cirsium arvense) is a creeping perennial that reproduces from vegetative buds in its root system and from seed. Long recognized as an agricultural pest, it has become an ever-increasing problem in natural areas—along riverbanks, on sand dunes, and in wetlands up and down the river.

A relative of the sunflower, it was introduced to the U.S., probably by accident, in the early 1600s. It reduces habitat for native species by diminishing shade, along with sucking up vital nutrients from the soil. Canada thistle is capable of producing a three-foot long rhizome (lateral roots) which can regenerate more sprouts. This “noxious weed” is identified by a lavender flower pod, prickly leaves, and a spiny stem that can reach up to four feet. It produces an abundance of bristly-plumed seeds which are easily dispersed by the wind.

Control can be achieved over a number of years through a variety of methods, including hand-cutting and mowing. The application of herbicides is more effective than mowing and burning when eradicating the weed. Due to its perennial nature and extensive root system, entire plants must be killed in order to prevent re-growth from rootstock.

Musk Thistle

Musk, or nodding thistle (Carduus nutans) is an aggressive, biennial herb with showy red-purple flowers and painful spiny stems and leaves. Mature plants range in height from 1 ½ to 6 feet tall and have multibranched stems. Leaves are dark green, coarsely lobed, with a smooth waxy surface and a yellowish to white spine at the tip. The spiky flower buds are distinctive. Each plant may produce thousands of straw-colored seeds adorned with plume-like bristles that are then spread by the wind.

Wildlife and livestock don’t eat this plant; therefore, selective grazing leads to severe degradation of native meadows and grasslands as animals focus foraging on native plants, giving musk thistle a competitive advantage. In its first-year rosette stage, the plants may reach up to four feet in diameter, crowding out prairie and pasture plants. Musk thistle easily spreads rapidly in areas subjected to frequent natural disturbances such as landslides and flooding.

A native of western Europe, musk thistle was introduced into the eastern US in the early 1800s and has been declared a noxious weed in many states. Musk thistle is threatening lands along the river’s banks and flood plains with its ability to overrun native grasses. Control of this plant is very difficult as its seed remain viable in the soil for over ten years.

Hand pulling is most effective on small populations and can be done year-around, though it is most effective before the development of seeds. Chemical and biological control options can be applied but each method has its drawbacks.

Russian Olive

Russian olive (Elaegnus angustifolia), also known as oleaster, is a shrub or small tree that can grow to 30 feet in height. Six feet of growth per year is not unusual. First cultivated in Germany in 1736, Russian olive was introduced into the U.S. in the late 1800s and was planted as an ornamental and for wind breaks. It subsequently escaped into the wild. One can easily recognize Russian olive by its dense covering of small silvery leaves.

Many birds eat the small cherry-like fruit and drop the seeds to the ground, which assists in the spread of the shrub. This invasive plant can be found along streams and in open fields. Many native areas have been dominated by the shrub’s ability to reproduce and deplete soil nutrients.

Once established, Russian olive is difficult to control and nearly impossible to eradicate. Most efforts to control it have been met with limited success. Cutting trees and then spraying or burning the stumps has proven to be an effective means of control. Total removal with heavy equipment has also proved successful.

Eastern Red Cedar

Other Invasives

Many other imported plants have become invasive or are potentially invasive. One is the Spiny Plumeless Thistle, recognized by the spiny ribs on the bloom stalk and reported to hybridize with Musk Thistle. Russian Thistle first appeared in Bon Homme County, South Dakota mixed with crop seed. The dried plants became the tumbleweeds that were symbolic of the drought of the 1930s.

Other nonnative invasives include hoary cress, yellow starthistle, common bindweed, Eurasian water milfoil, and various varieties of toadflax and knapweed.

All of these species can have a negative impact on natural areas, as well as on crop and pasture land.

A native plant, Eastern Red Cedar, has also become invasive. Since today’s pastures are seldom, if ever, burned as the native prairie was, these trees often take over grazing land.