Top Vertical or Spiky Flowers to Grow in Your Garden

by Erin Marissa Russell

Like vertical flowers or spiky flowers? Here are some options for you. Gardeners who put lots of thought and planning into their garden schematics have a foolproof rule for designing stunning compositions. The back row of a flower bed should feature tall plants for a dramatic backdrop, medium-height blooms fill out the middle, and plants on the border at the foreground should be the smallest.

This simple approach to planning a garden results in a display that shows each flower off to maximum effect, because plants are arranged by height with the shortest ones closest to the viewer.

Taken as a whole, a bed with flowers staggered by height gives a balanced impression, drawing the gaze up and down along the visual field, where viewers find something interesting to behold no matter where they look. Blossoms that sit high atop long stems won’t hide more squat specimens from view with this gardening strategy, either.

As a general rule, gardeners following this system choose flowers that are at least two feet tall for the back row, 18 to 24 inches in the middle, and shorter than 18 inches in the front border. By far the most fun flowers to select and shop for are the lanky stunners that stretch toward the sky. Not only do the tallest plants fill the most vertical space—because they’re larger in general, these statuesque flowers tend to also have the biggest blooms, lighting up the back row with vibrant swaths of color.

Keep reading for our picks to add height as well as high drama to your garden layout with spiky vertical flowers. We’ll also include care instructions for each plant we recommend so you can get an idea of how the flowers we select will fit into your garden, your routine, and your climate.

Angel’s Trumpet Flowers

The angel’s trumpet plant is actually a small tree, and at peak conditions, they can stretch to 30 feet high. Yours is more likely to range between 15 and 20 feet once it’s established in your garden. However, it’s common to see up to six feet of growth in an angel’s trumpet tree’s first year. If you choose to grow angel’s trumpet in a container, you can expect your plants to reach four to 15 feet. Also called brugmansia, the tree’s sheer height isn’t the only way it can add vertical intrigue to your garden. The blooms themselves hang from the branches in pendulous bells and appear from early summer through fall, measuring between six and 10 inches.

While they’re producing new growth, be sure to give your angel’s trumpet plants plenty of water. In container gardens, a self-watering pot can help keep these thirsty trees hydrated. If they’re producing pale leaves, wilting, or falling prey to disease or infestations, lack of water is often the culprit. Otherwise, choose a spot with fine, well-draining soil that’s rich and fertile. Add a layer of mulch to help keep moisture available for the plants. Use an all-purpose fertilizer once a month from spring to early fall, and take measures to protect angel’s trumpet plants from snails and slugs.

The angel’s trumpet comes from South America, so it’s a subtropical plant that does best in USDA growing zones 9 through 12. It’s possible to cultivate these beauties in chillier climates, though. When the weather starts to dip toward freezing, stop giving fertilizer to angel’s trumpet plants and decrease your watering regimen. Then just dig them up before the first frost in your area, maintaining as much soil around the roots as you can, then store them in a dry place that will stay below 50 degrees Fahrenheit. Cellars or basements can be an ideal location for overwintering.

Water your angel’s trumpets a few times during the winter while they’re in storage. Ideally, you’ll want to keep the root ball just moistened. When you reintroduce these trees to your garden the next spring, just loosen the roots with your fingers or a gardening trowel to encourage new growth. Be advised that the angel’s trumpet’s beauty has a dark side—compounds contained in the plant called tropane alkaloids have serious health risks if ingested, including hallucination, paralysis, and even death.

Cannas Flowers

Cannas are some of the most iconic flowers you can choose, known for their palm-like leaves and cane-like spires in bronzy burgundy or glossy deep green. The flowers are clustered petals of flame orange that sit atop spires that stretch as tall as a man. Their striking blooms adorn the garden beginning in late spring. A smattering of canna lilies along the edges of your garden is akin to lighting colorful floral torches around the perimeter.

Plant canna lilies outdoors at the beginning of the summer, at the same time you’d sow tomato plants. If your climate doesn’t offer a lot of time in the growing season, you may choose instead to start your cannas indoors in containers. To plant cannas in the garden, loosen about 12 to 15 inches of soil in the chosen location. Position each rhizome with the eyes facing up in a hole two to three inches deep and spaced one to four feet away from other cannas. Cover newly planted rhizomes with soil and press it down firmly. If you choose to plant from seeds instead of rhizomes, be aware that cannas tend to have low germination rates and will require filing or an acid bath to pierce the seeds’ tough exterior.

The needs of canna lilies are simple: provide them with plenty of sun and moist, rich soil, and they’ll require little else of you. Water heavily during dry periods and continue to water throughout the summer whenever your area receives less than an inch of rain. Stake taller plants as needed, and deadhead spent blooms to encourage fresh flowers. Once a stalk stops producing blooms, you can cut it to the ground so other cannas nearby get extra light, or you may choose to maintain the foliage, which will flourish until the first frost. Be vigilant for common ailments of cannas: slugs, snails, spider mites, caterpillars, rust, fungal leaf spot, bacterial blight, bean yellow mosaic virus, and tomato spotted wilt virus.

In USDA growing zones 7 through 10, you can leave cannas in the ground throughout the winter. A heavy layer of mulch over the ground where cannas are planted will help to protect them against chilly weather as well as locking moisture into the soil for them. Gardeners in other zones will need to lift rhizomes out of the garden and store them, spaced apart so as not to touch, in peat or leaf mold kept just moist in a frost-free location. Those in the deep South of the United States should let cannas grow for three to four years at a time before digging up cannas to separate the roots and nourish the soil or move to a fresh spot. When dividing the roots, make sure to keep at least one node on each new piece for new leaves to sprout from.

Castor Bean Flowers

Castor bean plants are beloved by gardeners for the dramatic, statement they make in the garden. The plants can stretch up to 10 feet tall in just one season, and they feature leaves as large as dinner plates. In addition to its size, the castor bean’s foliage is unique for its tropical range of hues. Leaves can appear in shades of blue or burgundy. The castor bean bursts into bloom with red inflorescences eight to 18 inches tall, and these female flowers are followed by more delicate white male flowers The spiny seed pods may be white, green, or red, but all mature to a brown hue. The combination of these unique qualities make castor bean an eye-catching accent plant to provide height in your garden.

Be advised that the castor bean’s seeds are quite poisonous due to the ricin they contain—eating four of them can kill an adult, while ingesting less than that has serious consequences, including vomiting and convulsions. Animals and birds are also susceptible to poisoning if they ingest castor bean seeds. These plants should be grown out of the reach of children, or at a minimum, flowering spikes should be trimmed if children will be near the plants.

There are plenty of common choices for vertical or spiky flowers to add to your garden, such as sunflowers, gladiolus, or hollyhocks. We’ve selected these to present because they’re little-known treasures that many gardeners may not be aware of. We hope you’ve found a few new options for your garden.