10 Tall Annuals for 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. These 10 plants 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 surprisingly quickly.

  • 01 of 10

    Ageratum Houstonianum

    Ageratum houstonianum
    Marie iannotti

    Maybe you are familiar with the shorter ageratum varieties sold in garden centers. They have the familiar blue flowers in a compact size. It is easier for growers to ship compact plants and for garden centers to display them, so larger varieties often get pushed out of the limelight.

    Ageratum houstonianum is not a new introduction, but many of its newer cultivars top out at 4 to 6 inches. Ageratum "Blue Horizon" can quickly grow to 30 inches in height and a cluster of these plants will form a blue haze that attracts butterflies and other pollinating insects.

    They can burn out in the hot sun and often fair better with a little partial shade at least in the afternoon. 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.

    Find a spot where they will be happy growing, keep them deadheaded, and the plants will repeat bloom throughout the summer.

  • 02 of 10

    Amaranthus

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

    There are several notable Amaranthus that make an impact in the garden. Old fashioned love lies bleeding or Amaranthus caudatus, can grow 3 to 5 feet tall with long panicles of dangling flowers.

    Amaranthus hypochondriacus, prince's feather, grows to about 4 feet and has flowers held in upright panicles in shades of red, purple, gold, and green.

    Another popular species is Amaranthus tricolor, which you may know as Joseph's coat or summer poinsettia. The flowers are not much to see, but when the plant starts to flower, the green leaves break up into a party of tropical colors from red to purple to gold.

    All of these plants can be grown quickly from seed, although you might want to start them indoors and wait to transplant the seedlings when they reach at least 6 inches tall.

  • 03 of 10

    Castor Bean

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

    Castor bean, Ricinus communis, is often shied away from because the seeds are extremely poisonous and the leaves can be an irritant. If you have young children, this is not the plant for you. 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.

    To get the largest plants, you will need to either buy seedlings or start seeds early, 6 to 8 weeks before your 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.

    To get your plants to shoot up, give them a soil rich in organic matter and plenty of water. Castor beans plants can easily top 10 feet. Many plants will keep growing up to 15 feet.

  • 04 of 10

    Cleome

    Cleome in Bloom
    Cleome is called spider plant because of the "legs" reaching out of the flowers. Marie Iannotti

    Cleome hassleriana, or 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. You will probably get some self-sown flowers if you grew them the year before. However, they do not tend to germinate until the soil warms up. 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.

    Cleome does not usually have pest problems, but they do have another growing caveat. Some people think their musky odor is a bit too much like a skunk. Not everyone detects this odor. In fact, cleome is even used as a cut flower. But you might want to check them out before you plant it in yours.

    Continue to 5 of 10 below.
  • 05 of 10

    Cosmos

    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 anytime around your last frost date.

    Cosmos 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.

    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 will self-seed. Some gardeners find it a nuisance, but they are easy enough to pull out, while young.

    Leave the plants standing through winter. Birds love their seed.

  • 06 of 10

    Kiss Me Over the Garden Gate

    Persicaria orientale
    Kiss Me Over the Garden Gate has spiky pinkish flowers that dance above the leaves. Francois De Heel / Getty Images

    There are several notable Persicaria species and some, like Persicaria polymorpha, are perennial. Persicaria orientale, also known as kiss me over the garden gate or knotweed, is a quick growing annual with spikes of purple-pink flowers that bloom above the foliage.

    You can direct sow or start seed indoors, 4 to 6 weeks before your 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.

    It is called knotweed because of the nodes or joints along its stem. It is no relation to the invasive Japanese knotweed.

  • 07 of 10

    Nicotiana

    Nicotiana sylvestris
    Nicotiana sylvestris can quickly reach 5 ft. tall, with the wonderful bonus of fragrance. David Q. Cavagnaro / Getty Images

    Flowering tobacco, Nicotiana sylvestris, 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.

  • 08 of 10

    Sunflowers

    Teddy bear sunflowers
    Teddy bear sunflowers. Image Source / Getty Images

    Sunflowers are probably the first flowers you think of when you go looking for tall annuals. Annual sunflowers, Helianthus Annuus, used to be a late bloomer, but there are some new varieties that are day neutral, meaning they do not require a long day length to start setting buds that begin blooming in mid-summer.

    The traditional yellow sunflower still charms, but you also find them in rich burgundy, deep mahogany, and many bi-colors.

    You can start seed indoors 2 to 4 weeks before your last frost date, but they do not like their roots disturbed, so plant them in peat or paper pots. However, they grow very quickly and seed that is direct sown will catch up to the plants you started indoors.​

    Continue to 9 of 10 below.
  • 09 of 10

    Tithonia

    Mexican Sunflower (Tithonia)
    Tithonia flowers are quite a bit smaller than those we associate with sunflowers, but they are certainly profuse. Marie Iannotti

    Tithonia rotundifolia, Mexican sunflower or torch flower, seem to have disappeared from gardens lately. That is a shame because this cheery, bright orange flower is easy to grow and virtually pest free.

    The plants can reach 5 feet in height, although the plant industry keeps introducing "dwarf" varieties. Give tit a moderately rich soil and then stand back and watch it grow. The plant loves hot days and does not mind humidity or a brief drought.

    Tithonia takes awhile to start blooming. To speed things along, you can start seed indoors 6 to 8 weeks before your last frost. It needs some light to germinate, so press the seeds against the soil, rather than covering them. The seedlings grow fast and will need to be repotted in larger pots regularly or they will become stressed and try to go to seed.​

  • 10 of 10

    Verbena bonariensis

    Verbena (Verbena Bodariensis)
    Jacqui Hurst / Getty Images

    Verbena bonariensis, tall verbena or Brazilian vervain, is an unusual plant that finds its way through your garden. It 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. 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 and the following year you may have more than you need, but it is easy enough to pull out and adapt well if transplanted elsewhere. Do not panic if you do not see it early in the season. The seed does not germinate until mid-spring.