Popcorn Cassia (Senna didymobotrya) — In-Depth Care Guide

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Senna didymobotrya, also known as Popcorn Cassia, is a plant originating from the tropical regions of Central and Eastern Africa.

Now recognized as a Senna, it was originally categorized as a Cassia and that part of the name has stuck, hence it’s common name, Popcorn Cassia.

The popcorn aspect of the name comes from the unique scent produced by rubbing the foliage.

The scent is sometimes referred to by the slightly less appealing term ‘wet dog’. 

Senna didymobotrya is a perennial that displays spikes up to 30 cm high, which are covered in bright yellow, roundish flowers that emerge from dark buds and resemble popcorn once they open up.

Blooming in late summer, Senna didymobotrya adds a late shot of vibrant color to the garden.

The leaves are pinnately compound, meaning each leaf is divided into smaller leaflets which grow on either side of the central stalk.

It is sometimes grown as a green manure but its striking flowers, fast growth time and relatively easy maintenance make it a regular in gardens too.

Despite being native to hot climates, Senna didymobotrya is suitable for growing in cool climates.

Occasionally grown as a multi-branching shrub or tree of up to around 8 meters tall, its standard size is around 2-4 meters and it is often kept short to get the most from its flowers.

In cooler climates where it gets too cold over winter, it can be grown as an annual.

 

 

Senna didymobotrya care

Senna didymobotrya  is a relatively easy plant to care for and can last for years in the right conditions. It likes direct sunlight, plenty of water and free-draining soil to flourish. Apart from its unique scent, it is favored for its bright yellow flowers which keep your garden in color until late summer and you can enhance this by adding fertilizer once a month through the growing season. It can be grown indoors or outdoors, in borders or pots. Naturally occurring in tropical climates, it will do best in hotter climates but can be grown as an annual in cooler temperatures so can be enjoyed by people anywhere and everywhere.

 

Where to grow your Senna didymobotrya

Senna didymobotrya can be planted in a border among annuals and other perennials. It is best placed towards the back of the border due to its height and rapid growth, but it needs plenty of direct sunlight.

This plant displays large feathery foliage which complements other large-leaved plants perfectly. Its unique leaf structure also adds extra interest to a colorful border.

Alternatively, Senna didymobotrya can thrive in a container as a specimen piece.

It will also grow well in a greenhouse or conservatory where it will relish a position with full sun.

 

Watering

Your Senna didymobotrya will require plenty of water but must be kept in well-draining soil. If planted in a border it is best to water thoroughly once a week rather than a little every day.

As a guide, when watering you should aim to provide sufficient water for it to penetrate to a depth of around 15 cm. This is to ensure the roots are encouraged to reach down for water as the week goes on and will encourage a healthier plant.

This is particularly important in the first year of the plant’s life. Be careful not to water too frequently as this can lead to root rot and can starve the roots of oxygen which they need to for strength.

Once it is fully established, Senna didymobotrya should be drought-tolerant, although for optimum health and vibrant blooms It should be watered as directed.

When growing Senna didymobotrya in pots or containers, make sure there are drainage holes in the container and that you place a layer of stones or gravel at the base of it before adding soil.

You should water sufficiently for it to start coming through the drainage holes. 

If you are growing your plant outside, bear in mind the amount of rain that falls. If you get more than 2.5cm of rain in a week, you may not need to water the plants manually.

Of course, this depends on other environmental conditions such as the temperature and the amount of sunlight it is exposed to.

If you are unsure, check the soil for moisture levels to help you decide whether manual watering is necessary. The same process applies to Senna didymobotrya grown indoors.

Wherever possible, water plants early in the day or late in the afternoon to conserve water and reduce plant stress.

You should water early enough in the afternoon that the water has sufficient opportunity to dry from the leaves of your plant before nightfall. Moisture on the leaves overnight can cause rot or fungal infections.

 

Temperature

Senna didymobotrya is a sun-loving plant that enjoys temperatures of 80-90°F. It can withstand cooler climates but if temperatures begin to regularly drop below 40°F, growth will slow down significantly.

If night time temperatures fall below 30°F, the plant may benefit from being overwintered indoors. It will not take kindly to being exposed to frosts.

The other option is to put it into a semi-dormant state.

This can be done by cutting the plant back to around half its size and then placing it in a pot which is kept in a cool garage with a light breeze for the duration of winter.

Do not water your plant while it is in a semi-dormant state. 

 

Humidity

Senna didymobotrya requires high levels of humidity so ideally it should be above 60. When kept indoors, it is unlikely that you will be able to achieve these levels of humidity – or that you would want to – so consider that when working out your watering schedule and adjust it accordingly.

If you are growing Senna didymobotrya outside and live in an area of high humidity, it should thrive and grow well. In less humid areas it may not grow as quickly but should still stay healthy provided you care for it well. 

 

Fertilizing

Senna didymobotrya grows best in rich soil. To encourage healthy blooms, fertilize once a month with a water-soluble fertilizer (such as 20-20-20) during the growing season.

The application of fertilizer should replace a regular watering and not be an additional soaking.

Make sure you stick to the guidelines and measure it out carefully as too much fertilizer can burn your plants and prevent them from growing.

 

Air circulation

Good air circulation is important for Senna didymobotrya to prevent fungal infections and rot. The plant is most susceptible to these types of problems in its infancy and should be given plenty of space around it for air to flow.

It is recommended that plants are placed at least 60cm apart. Originating from tropical areas, in its natural habitat it will be subjected to heavy downpours followed by extreme heat which will help dry the leaves and prevent water from gathering in crevices.

If the area you live in does not naturally replicate this, you will need to ensure there is plenty of space for air to circulate. You may also need to dry the leaves manually if it cannot be done by natural air circulation and the heat of the sun.

If kept indoors, the plant will benefit from full sun but should also be given a regular flow of fresh air. This can be achieved via an open window or by being placed outside in the warmer weather if possible.

Not only will this help to dry the leaves, it will also provide your plant with the oxygen necessary to promote photosynthesis.

If growing Senna didymobotrya inside make sure you do not place it too close to an HVAC system or heating unit as this could cause it to dry out. 

 

Propagation

Senna didymobotrya can be grown from seed or from a root cutting. If you are growing it as an annual, it is best to grow if from a root cutting.

Root cuttings should be planted outside in spring after all risk of frosts has passed. As a guide, it is usually planted out around the same time as tomatoes. Root cuttings should be placed around 60cm apart and watered thoroughly once they are in the ground. 

If you want to grow Senna didymobotrya from seed, you will need to collect the seed pods which appear shortly after flowering.

The pods look similar to pea pods and typically grow to around 12-15cm in length. Each pod houses 16 smooth bean-like seeds which should be collected and stored. 

When spring comes around the seeds should be sown shallowly indoors. Prior to sowing, soak them in water for 24 hours to increase germination speed.

They should be kept indoors until all danger of frost has passed and then planted outside, spaced 60cm apart. 

 

Common problems with Senna didymobotrya

Senna didymobotrya is not generally prone to any significant pests or diseases but if too dry can be affected by aphids and if too wet can be susceptible to fungi.

One of the most common problems faced by people growing Senna didymobotrya is environmental conditions. If you do not live in an area that enjoys warm temperatures throughout the year, you may struggle to grow it as a perennial.

If that is the case, simply collect the seed pods after flowering and sow them the following year, remembering to start them off indoors in around February.

Alternatively, you can purchase root cuttings in spring after the last of the frosts and still enjoy this delightful and colorful plant as part of your summer garden.

 

Frequently asked questions about Senna didymobotrya

 

Why is my Senna didymobotrya not flowering?

If your plant is not flowering, the likelihood is that it is being kept in an unsuitable environment. Make sure it is in an area where it gets plenty of direct sunlight every day. The soil should be moist but not soaking and your Senna didymobotrya shouldn’t be exposed to temperature below 30° Fahrenheit as this will damage any emerging buds. 

 

How do I make sure my Senna didymobotrya survives the winter?

Senna didymobotrya is a naturally sun-loving plant. In hot climates it can be overwintered naturally but if the temperature regularly falls below 30°F you will have to overwinter it indoors in a pot or by making it semi-dormant. In cooler climates, Senna didymobotrya is usually grown as an annual rather than a perennial. 
 

Is Popcorn Cassia poisonous?

Despite its pleasant popcorn aroma, Popcorn Cassia (Senna didymobotrya) is poisonous and should not be eaten. In its native East Africa, it is believed to have medicinal properties but these are not officially recognized by any medical authority and the plant should not be consumed in any way.

 

Conclusion

Senna didymobotrya has become a popular plant in recent years as it is a very attractive plant that adds form and color throughout the spring and summer.

As an annual, it adds bright colors to the garden either as part of a border or in a container.

Provided it is given plenty of sunlight, rich soil and ample water, Senna didymobotrya should thrive and produce heavy blooms of stunning yellow flowers which are equally at home in a multi-colored arrangement or monochrome display.

Monochrome borders or containers require other elements in addition to color and Senna didymobotrya has those in abundance.

From its height to its stunning dark flowers which bring color as they unfurl, to the leaf structure and seed pods, this is a plant that adds texture as well as color to your garden.

If planting it as a perennial, the first two years will require the most attention.

After that time it should be fully established and your only real consideration will be providing it with sufficient water during the summer months and possibly overwintering it if temperatures dip significantly over winter.

It also produces many seeds which are not only aesthetically pleasing but can be stored to propagate more plants when conditions are right.

Wherever you choose to grow it, Senna didymobotrya will bring joy, interest and a pleasant aroma anytime you rub the leaves.