Smoothie Thunbergia By Jack Williams

This series offers growers unique colors and a choice of form — climbing or trailing.

Thanks to the efforts of people like the breeders at Sahin in The Netherlands, new colors of this popular vine are now available for growing and selling.

Watching the world of plants it is easy to see that vines are hot. Among the species available in vines is thunbergia; you know, that old-fashioned annual vine known to gardeners as “black-eyed Susan vine.” Clear, single colors like yellow and orange are already found in the commercial market. Thanks to the efforts of people like the breeders at Sahin in The Netherlands, new colors of this popular vine are now available for growing and selling.

The Smoothie series offers unique multi-color blooms in shades of pale yellow to red in bi-color patterns and distinct new colors, such as lavender-pink. These new colors were introduced to the market during 2004/05 and will be found throughout North America this spring. When grown as vines, thunbergia can be trained to climb and cover either lattice or bamboo sticks positioned in the pot. A popular and easy way to grow thunbergia is to use bamboo sticks to form a tri-pod structure on which plants can attach themselves and grow upwards. The resulting vines are not only attractive, but also very tough and able to withstand harsh conditions. These plants make outstanding climbing forms but can also be used to create trailing plants of substantial length, making this species ideal to use in large baskets and other high value product forms.


Cuttings can be slow to root, so either allow adequate time in propagation or purchase from licensed rooting stations.

Stick cuttings as soon as possible, as thunbergia are very likely to wilt. Stick one cutting per cell using a rooting hormone containing 3,000 ppm IBA. Maintain bottom heat until roots are visible (70-75° F). This will reduce stress on the cuttings and help speed rooting. Watch cuttings closely, never allowing the cuttings to dry out. If using stem segment cuttings, stick the cutting so the node is making contact with the media. With stem segment cuttings a pinch may not be necessary. When using tip cuttings a pinch is not required, but 7-10 days before transplanting it may be beneficial to improve branching and habit.

Beginning in the third week of propagation plants should be fed once a week with fertilizer containing 175 ppm nitrogen. Plants are ready for transplant in 5-6 weeks.

Growing on

Smoothie prefers sterile well-aerated mixes; the pH should be maintained between 5.8 and 6.2. Constant liquid feed at 200-250 ppm with a balanced liquid fertilizer is recommended. Watch phosphorus and ammonium nitrate levels. If these levels are too high, unwanted vegetative growth may occur. If chlorosis is seen on the new growth use iron sulfate as a drench (avoid contact with foliage) or iron chelate as a spray or drench. Osmocote or other appropriate slow-release fertilizers may be beneficial in supplementing a constant liquid feed program. EC should range from 2 to 2.5.

To encourage more flowers, avoid keeping plants too wet and overly fertilized; mild stress helps encourage flowering.

Once established, thunbergia prefers warm temperatures maintained at 70-80° F days and 60-65° F nights. Lower temperatures will slow growth and reduce flowering. Light levels should be 5,000-8,000 foot-candles. Levels below 5,000 foot-candles will cause stretch and reduce flowering.

Plants should be established pot tight but spaced before foliage touches. A 4- or 5-inch pot with one liner will finish in 10-11 weeks with one pinch at week 5. A 6-inch with 2-3 liners per pot will finish in 11-12 weeks with two pinches — one at week 5 and one at week 7 or 8. A 10-inch with 3-5 liners per pot will finish in 12-14 weeks with 2-3 pinches. Any additional pinches will add an additional four weeks to the growing cycle.

If high light levels are maintained and recommended soil fertility is met, as well as allowing the media to dry slightly between watering, the use of PGRs is probably not necessary.

As stems reach the top of the trellis or bamboo, it is beneficial to train the vines downward again rather than leaving them to wrap around themselves and continue upwards. This encourages more flowering and puts stems in a position to show flowers more predominately.

Watch out for a few pests: aphids, whiteflies, spider mites, leafminer and thrips. Also, keep a look out for root and stem rots.

Why Smoothie?

Every year I create the California Pack Trial schedule for Bridget, Catherine, Rick Schoellhorn and myself. Well, it is that time again, and I’m working feverishly to fit more than 25 visits into one week. It got me thinking about last year’s Pack Trials, and while I’m excited to go and bring back the newest varieties to share with you, there is so much more from the 2004 visit that hasn’t been covered in our Crop Culture Report; the Smoothie series is one.

Raspberry, the only purplish pink thunbergia on the market, and Apricot, a nice shade of orange/yellow with a hint of pink, have versatile habits. They can either trail for a nice hanging basket, or with the help of a lattice or stick, they can be trained into a vine. And, not only is Raspberry a very unique color, it also has added consumer value with the soft, velvety texture of its leaves. How do I know this? Jack made us hug it at Pack Trials. So, after Bridget and Catherine hugged Raspberry, it was my turn, and it was huggably soft, which made our long, trial-filled day a little bit better.

– Carrie Burns

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Jack Williams

Jack Williams is technical advisor at Ecke Ranch, Encinitas, Calif. He can be reached by E-mail at [email protected]

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