8 Fast-Growing Flowering Giants – For Easy Garden Privacy with Gorgeous Blooms

Imagine the tiniest seeds you sow now, in April, rising into a living tower of color and wow-factor in your garden by summer. Think vertically in your yard this year, and before you know it, that little seed will be an epic visual showcase for a border, a showy privacy screen, or a high-impact curbside focal point. These towering tall flowers show that big impressions start small. Whether you are looking to create a living wall of color at the back of a border, block a neighbor's view, or simply feel hugged by your garden, these picks show that verticality can be a beautiful thing.

Planting in layers is a thrilling way to take your gardening to the next level. Layering plants by height creates a unique visual appeal and helps you highlight the attributes of each plant. Tall plants are statements that anchor beds and borders, draw the eye up, and help to create depth. Use the back of the border effectively, and you create a lush backdrop that also makes shorter ornamentals pop. Taking advantage of every vertical inch helps you to create a space that feels established and intentional.

Start these tall plant ideas in April, and you’ll be surprised how quickly you can admire their towering blooms. If you’re after beautiful ornamentals that double up as privacy screen flowers, delivering color, structure, and seclusion, these are the sky-high bloomers to sow this month. Onwards and upwards!

Gorgeous Giants for Every Boundary

To reach the dizzy heights, these towering flowers need a head start. Most are fast-growing annuals, though we have included a few biennials and short-lived perennials that behave like giants in their first or second years. April sowing allows the root systems to establish deeply before the summer heat kicks in, providing the resources necessary to fuel 8-10 feet (2.4-3m) of upward growth in a single season.

Depending on variety and hardiness zone, you can sow outside or start indoors and transplant out later. Check your area’s last frost date to determine if you need to sow indoors and to decide when to transplant. If you are planting against a fence or wall, ensure tall plants have enough airflow. Don't jam plants against the edge, or you'll invite mildew. Also, avoid planting where there is wind exposure. Sort out stakes in spring, while there is less risk of root damage. These fast-growing beauties need a solid foundation and support to stand proud and reach their full potential.

You’ll need a site with 6-8 hours of direct sunlight for these gorgeous giants. Because they grow so much in a short time, regular feeding is also a must. Knowing your soil pH ensures these tall flowering plants can absorb nutrients. Test soil before sowing, using a meter like the Yamron 4-in-1 Meter from Amazon. If need be, amend with a little coarse sand or perlite to ensure the site is well draining, especially for red hot pokers or delphiniums. So, let’s check out our 8 high-impact beauties.

1. Sunflowers

As well as being the epitome of summer joy, sunflowers (Helianthus annuus) are classic tall border plants that flower from midsummer to fall. For the most striking transformation from little seed to towering flowers, grow giant sunflower varieties. Cultivars like ‘American Giant’ or ‘Cyclops’ can reach 8 feet (2.4m). Heirloom varieties like ‘Mammoth Grey Stripe’ produce massive heads spanning a foot across, providing a heavy-duty focal point that doubles as a bird feeder in the fall. Plant some “happy” with the lovely sunflower seed options available at Burpee, including Kong, Sunforest Mix, American Giants, and Candy Mountain.

Growing these sunflowers is easy. They grow best from seeds sown directly outside once the soil has warmed to 60°F (15.5°C). If you have a short growing season, you can start them indoors in peat pots (as they dislike root disturbance). Plant these easy annual flowers in a row in your sunniest corner to create a temporary summer hedge, and stake to help them grow straight and strong. Don't forget that their heavy heads will follow the sun, so ensure the faces will be looking toward your seating area. Pair these tall yellow flowers with climbing nasturtiums to cover their scruffier lower leaves.

2. Mexican Sunflower

The Mexican sunflower (Tithonia rotundifolia), is the unsung hero of the summer border. Reaching 6 feet (1.8m) tall, this annual is a pollinator magnet, particularly for monarch butterflies. Unlike the common sunflower, tithonia branches out, creating a bushy, wide screen covered in velvety, intensely orange or red daisy blooms. Cultivar ‘Torch’ is an award-winner known for its prolific flowering and heat tolerance. Start seeds indoors to get these striking flowers going sooner. Once transplanted, they’ll want full sun, good drainage, and only occasional watering.

When growing for a border, give these tall orange flowers plenty of horizontal space, at least 2-3 feet (60-90cm) apart, since they are as wide as they are tall. Don’t over-fertilize, as too much nitrogen leads to lush leaves but few flowers. They thrive in lean soil and are incredibly drought-tolerant once established. For a fiery display, plant with tall purple salvia varieties or zinnias. Their stems are brittle, so they appreciate being sheltered from high winds or supported with a light cage. Buy Sow Right Seeds Mexican Sunflower Seeds from Amazon for prolific orange blooms from midsummer until the first hard frost.

3. Delphiniums

Delphinium, aka larkspur (Delphinium spp.), provides a regal stature that few other flowering ornamentals can match. One noteworthy variety is D. elatum, which sends up architectural spikes that can reach 7 feet (2.1m) high. Hues can also be next-level brilliant. Cultivars like the ‘Pacific Giant’ series offer breathtaking cobalt and sky blue flowers, as well as tall purple flowers in shades of lavender, indigo and violet, often with a contrasting bee (center). Delphiniums bring a formal, English-cottage feel to any border, boundary or fence line, and flower from early to midsummer.

When growing delphiniums, they are mostly hardy in zones 3-9, and grown as short-lived perennials (or annuals in the south). Provide rich, moist, well-draining soil and a mulch to keep roots cool, and make sure they get some afternoon shade in warmer climates. Don't plant them in a windy spot without a trellis or some sort of windbreak. Staking is also important, as the flower spikes are top-heavy and will snap easily. These delicate giants are perfect companions for a rose border or foxglove planting. Buy Delphinium ‘King Arthur’ Seeds from Walmart for a burst of brilliant deep blue-purple along your border or boundary line.

4. Hollyhocks

Hollyhocks (Alcea rosea) are the quintessential cottage garden skyscrapers. Growing up to 8 feet (2.4m) tall, they bloom sequentially from the bottom up, creating a long-lasting pillar of vivid color with large flowers from June through August. From frilly apricot ‘Chater’s Double’ to moody, chocolate-burgundy ‘Blacknight,’ these towering plants offer a variety of textures. Traditionally grown against walls, they are the perfect masking plant for unsightly sheds, crumbling walls, or utilitarian fences, creating dazzling screens of mixed color in hues of yellow, orange, pink, purple, and white. One unique variety called ‘Blacknight’ is practically black.

When growing hollyhocks, ensure excellent air circulation and space flowers 18 inches (46cm) apart to prevent hollyhock rust, a fungus that affects lower leaves. Don't be afraid to sow them in April. While many are biennials (blooming in the second year), modern strains will bloom the first year if started early enough. They love deep, rich soil, but make sure you factor in excellent drainage. Surround with lower-growing perennials like cranesbill geraniums to hide the stalks. Buy ‘Country Mix’ Hollyhocks from Burpee for a jamboree of color. Once established, they’ll reseed each year to give you summer after summer of striking flowering screens.

5. Amaranth

Amaranth, specifically ‘Love-Lies-Bleeding’ (Amaranthus caudatus), offers a completely different silhouette for vertical gardening and privacy screen landscaping. Instead of flowerstalks pointing upwards, its heavy, crimson tassels “weep” from 5-8-foot (1.5-2.4m) stems. This magnificent edible and ornamental all-star presents with velvety magenta clusters that spill in elegant fashion through summer into fall. Cultivars like ‘Hot Biscuits’ offer rich copper tones, while ‘Coral Fountain’ provides softer, pinkish hues.

You can start amaranth seeds indoors or outside. They need full sun or a little shade in warmer climates. The soil can be poor; in fact, soil that is too fertile can hinder flower production. Water only if you’re getting less than an inch (2.5 cm) of water per week. They are incredibly tough and can handle the humidity of the south and midwest with ease. Deadhead regularly to encourage new growth. Perfect for a red garden, you can also pair them with ornamental grasses for a prairie-inspired privacy border. You can buy ‘Love Lies Bleeding’ Seeds from Amazon.

6. Red Hot Poker

If you’re after drama and impact, these tall red flowers can create a vibrant shield of color around the edges of your yard from late spring to midsummer. Red hot pokers or torch lilies (kniphofia) bring a torch-like glow to a border or boundary. While a few varieties stay small, archetypal giants like classic ‘Prince Igor’ (orange-red) reach 6 feet (1.8m). Their unique, spiky texture contrasts beautifully with soft-leaved plants. You can also get gold and white varieties like ‘Lady Luck’ kniphofia. As perennials in zones 5-9, they provide a permanent vertical structure year after year.

Sow seeds directly outside in warmer areas or start indoors in cooler climates. Plant these high-risers in the sunniest spot you have, and ensure the planting sites are relatively deep for these long-rooted ornamentals. Make sure the soil is well draining. Hardy in zones 5-9, they are excellent for attracting hummingbirds, making them a living bird feeder for your yard. Plant in clusters of three for a vivid explosion of color like a fireworks display frozen in time. Buy Red Hot Poker Seeds from Amazon.

7. Castor Bean

The speed of growth associated with the vibrant castor bean (Ricinus communis) is staggering, as is its climb skyward. This striking annual can reach 10 feet (3m) in a single season, producing massive, dark star-shaped leaves. Cultivar ‘Sanguineus’ features blood-red stems and bronze leaves. Castor bean provides a dense, leafy mass that is unsurpassed for a summer privacy screen. Both female and male flowers appear on the same plants in summer and fall. As a bonus, the flowers develop into attractive, spiky seed pods in the fall.

Every part of the plant is toxic, so it’s not ideal if you have pets or small children – and you need to wear gloves when handling seeds. Give transplants a spot with full sun and rich, moist soil that drains well. If soil is poor, use a balanced slow-release fertilizer every month. Because it grows so fast, this statement ornamental is a heavy feeder. It looks spectacular paired with other tropical-looking plants like cannas or elephant ears for a backyard-resort vibe. Buy Mountain Valley Seed Company Castor Bean Seeds from Walmart for the ultimate fast-growing privacy screen.

8. Flowering Tobacco

Species of nicotiana can be amazing for scale as well as fragrance. Tall types include N. alata and N. sylvestris, which can become a giant, sending up stalks 5-6 feet (1.5-1.8m) high and topped with exploding stars of fragrant trumpets. Growing nicotiana, you’ll find it is the perfect moonlight garden plant, as the scent is most intense at dusk. It adds a sophisticated, airy height that doesn't feel heavy or bulky, while still providing an effective boundary through summer in hues of red, pink, white, yellow and green. Try ‘Heaven Scent’ Nicotiana Seeds from Burpee for curtains of color draped on stalks 8 feet (2.4m) tall.

Grow as an annual and start seeds indoors in spring. It will grow quickly from seed, but be aware that it is toxic. Transplant seedlings a couple of weeks after the last frost in a spot with full sun and good drainage. They prefer moist, rich soil and can handle afternoon shade better than the other giants on this list. A simple, stylish wooden trellis will help guide stalks along a wall. Water regularly to keep the soil moist, and use a balanced fertilizer for optimum flowering. Pair with silver-foliage plants like ‘Silver Mound’ Artemisia to enhance the ethereal evening glow. Don't be surprised if flowering tobacco self-seeds. If they like a spot, they’ll return for years.

Shop Towering Flowerers

The sky’s the limit with these gorgeous giants – and April is the perfect "get set" moment for kickstarting a summer of vertical stunners. Whether you are looking for the classic drama of a sunflower or the exotic hues of amaranth, these epic flowering stunners will help you create a living screen of flower power in your border.

Sowing Secrets for High Summer

Sowing in April (indoors in the north or outdoors in the south) allows these plants to maximize the period where they focus on building stems and leaves. If you wait until June, many will feel stressed and may bloom prematurely at a shorter height. By starting now, you’re giving them the runway they need to really take off.

When sowing near a boundary, remember the drip line. Walls often create a rain shadow where the soil stays bone-dry even after a storm. Plant at least 12-18 inches (30-45cm) away from the structure and supplement with manual watering. To avoid stunting, check the spacing requirements on the seed packets. It’s tempting to crowd them for a thicker screen, but overcrowded giants will compete for nutrients and wind up spindly. Give each huge plant the best chance at reaching for the skies!

Don't move indoor-sown seedlings outside until the last frost has passed, and remember to harden off. Add stakes at the time of planting to avoid stabbing the root ball later. Mulch in May to retain the moisture these high achievers crave. A 2-inch (5cm) layer of finely shredded bark mulch is the best bet for most towering flowers, such as Back to the Roots Organic Premium Mulch, which you can get from Amazon. Keep a good few inches away from the stems of hollyhocks and Mexican sunflowers, though, to ensure plenty of air circulation and prevent fungal hiccups.

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