Sennas: Garden Gold

Popcorn cassia (Senna didymobotrya) is a tender garden plant for containers and gardens.

Gardeners are just beginning to learn about the benefits of adding bold, golden-flowered sennas to their gardens. These members of the pea family naturally fortify soils with nitrogen in addition to producing large clusters of brilliant gold flowers and lush foliage. They lend tropical good looks to landscapes and beds, and their flowers are also draw pollinating bees and butterflies. Some are even butterfly host plants.

Most sennas are long-blooming. Some are large, shrubby, and need space to grow. Others can be grown as tender perennials that stay small in summer, making them suitable for growing in flower borders or containers. Species exist worldwide, but quite a few are North American natives. Overall, sennas have the benefit of being very resilient and tolerant of high heat. Some are even desert plants perfect for xeriscaping.

Here are just a few attractive sennas to consider cultivating in your landscape or pollinator garden this season.

Sennas for Gardens

Popcorn cassia (Senna didymobotrya, USDA Hardiness Zones 9-11): This has become the most popular senna on the market. It is native to Africa where it grows as a large 6- to 8-foot shrub, but popcorn cassia works well as a tender perennial for containers and gardens. In the heat of summer, it bears nonstop candles of golden flowers that are dark in bud. Its flowers feed bees and butterflies, and it is also a host plant for various sulphur butterfly caterpillars. Cuttings can be taken in fall and overwintered for outdoor cultivation the following season.

Many sennas are host plants for various sulphur butterfly caterpillars, including the cloudless sulphur butterfly.

Feathery cassia (Senna artemisioides, USDA Hardiness Zone 8 to): With fine, silvery foliage and loads of fragrant golden flowers that bloom non-stop, this Australian desert plant grows best in arid to semi-arid regions, though it can also be grown as a container specimen, if provided very sharply drained soil, such as Black Gold Cactus Mix.

Feathery cassia (Senna artemisioides) is adapted to desert conditions.

Maryland senna (Senna marilandica, Zones 4-8): Native to open woods and dry roadsides across the eastern United States, this tall, tough perennial deserves more attention from American gardeners. It forms bushy clumps of compound leaves that may reach between 3 and 6 feet, depending on the selection. In July and August, it becomes topped with large clusters of flowers that may be pale yellow, golden yellow, or pale orange. These are especially attractive to bumblebees, and it is a host plant to sulphur butterflies. The flowers are followed by large, dark, pendulous seed pots. Plant it in spacious perennial borders where a large, impressive garden plant is needed.

Maryland senna (Senna marilandica) is a tall, very hardy North American species.

Silverleaf cassia (Senna phyllodinea, Zones 9-11): Another xeric species from Australia, silverleaf cassia is an exceptionally pretty bushy shrub with slender silver leaves. Its masses of golden flowers bloom from winter to spring. Grow it in southwestern gardens with rocky or sandy soils. It has the potential to be invasive, so plant it away from natural areas.

Silverleaf cassia (Image by Desert Horizon Nursery)

Golden Wonder Senna (Senna splendida, Zones 9-11): In warm-winter regions of the United States this South American tree senna produces large clusters of bright gold flowers from early fall to early winter. The trees can reach 16 feet and are semi-evergreen.

Golden Wonder Senna (Image by Alex Popovkin)

Cultivating Senna

Overall, sennas thrive in full sun. Dryland species require very well-drained soils, but all others will grow well in average fertile soil with moderate to good drainage. Amend the soil of in-ground plantings with plenty of Black Gold Garden Soil amendment, which has added fertilizer and rich organic matter. Container-grown popcorn cassia will thrive in large containers filled with Black Gold Natural & Organic Potting Mix.

Plant any one of these golden beauties in your hot summer garden for resilient plantings sure to draw lots of pollinators to your flower beds and landscapes.

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Big, Bold, Tropical Foliage Plants

Brilliant crotons and cascading Scaevola aemula ‘Blue Fan’ look striking in this container planting.

Big, bold, tropical plants look amazing in summer gardens and large containers and drink up the summer heat and humidity. Ornamental bananas, exotic elephant ears, upright sansevierias, strappy cordyline, and colorful croton are typically grown only indoors or way down South, but they thrive in any place that’s steamy. Placing them in the right spot in summer with the bedding plant companions is part of the fun.

Big Leaves

Codiaeum variegatum

The multi-colored visual pop of croton (Codiaeum variegatum) leaves look good in any bold planting. The Southeast Asian shrub likes it as hot and humid as it gets and looks great in partial shade or sun. Provide it with quality, well-drained potting soil (Black Gold All-Purpose Potting Soil with RESiLIENCE®) and regular water, it will perform well. There are many varieties with leaves that vary in color and size. (Visit the Croton Society webpage to learn more.) The manageable size of croton makes it a good plant to pair in containers with colorful bloomers, such as Lantana camera, cascading Scaevola aemula ‘Blue Fan’, and tropical Hibiscus rosa-sinensis, which has brightly colored disc-shaped flowers.

Cordyline fruticosa 'Kiwi'
Cordyline fruticosa ‘Kiwi’

Tropicals with bold, strappier leaves include the West Pacific native Cordyline, African Sansevieria, and corn plant (Dracaena fragrans). Plant these in beds or large pots for a dramatic impact. The more colorful the foliage, the better. Cordyline fruticosa ‘Kiwi’ has a soft but notable color with its pink-, cream-, and green-striped foliage. For pretty gold and green variegated foliage, choose Dracaena fragrans ‘Golden Coast’ with its leaves striped with gold, dark green, and medium green. The nearly vertical leaves of the drought-tolerant Sansevieria trifasciata look great on their own in a pot or paired with a cascading accompaniment of plants at the base, like Dichondra argentea ‘Silver Falls’ or creeping sedums. 

Bigger Leaves

Elephant ear or ornamental taro (Colocasia esculenta), originates from Southeast Asia and has big leaves that come in lots of attractive colors. Choose extra colorful purple-black cultivars and cheerful chartreuse or gold variants. Bicolors, such as the green-leaved, purple-speckled ‘Mojito’, also make a big garden statement.

Colocasia esculenta ‘Mojito’

Elephant ears are moisture-loving and grow well in wet soils if given the opportunity. They make excellent container specimens and should be planted in an ultra-organic potting soil with a high water-holding capacity, such as Black Gold® Moisture Supreme Container Mix with RESiLIENCE.


Biggest Leaves

Gigantic-leaved plants require tons of space but look spectacular and fun if properly placed in the landscape. Add one plant to a single pot. Abyssinian red banana (Ensete maurelii), with its broad, reddish green leaves, or the massive giant elephant ear (Colocasia gigantea), with its 5-6′ leaves, command visual attention and are best planted where big, focal statements are needed. An open patio area or broad, open

Ensete maurelii

fence line or border would be perfect. The 6-8′, banana canna (Canna ‘Musifolia’), which has reddish leaves much like those of Ensete maurelii, is another impressive easy-to-grow garden plant. Grow these in full to partial sun alongside finer-leaved, colorful companions. Tall amaranths, purple-red-leaved Hibiscus acetocellus, and formidable ornamental grasses are all great choices.

Grow these bold ornamentals if you are seeking to fill space fast and want your garden to feel like a tropical paradise. Once the threat of frost has passed you can plant them outdoors, but don’t expect them to take off until the warm, humid weather of the summer months begins. Then, watch the magic!