Thunbergia gardenia vine in bloom.
image by Afrodita_nz:commons.wikimedia.org
Clock vine, or thunbergia, is a genus of tender perennial flowering plants named for the famed Swedish botanist Carl Peter Thunberg. Climbing and vining in their growth habits, thunbergia's bloom size, shape and color can vary widely by varietal. Most varietals are hardy in USDA zones 9a through 11 and they are grown as annuals in cooler climes. Thunbergia performs well when supported on arbors or tuteurs, and is also widely grown in containers and hanging planters.
Plant thunbergia where it receives full sun exposure throughout the day. In warmer and/or drier climates, some midday and afternoon shade is welcome and will not significantly reduce bloom. Provide your thunbergia with a nutrient-rich, well-drained soil that holds moisture. When grown as a perennial, amend the soil with compost and well-aged manure at planting, and scratch more into the surface soil once a year to boost the nutrient content.
Water your thunbergia regularly so that its soil is consistently and evenly moist. Depending on your climate and plant setting this may mean daily watering to watering once every 8 days. Monitor the soil carefully by touch, as you do not ever want it to dry out completely. In very dry climates, mulching around the base of the plant with shredded bark or cocoa hulls will help conserve soil moisture.
Provide sturdy staking for your thunbergia so it can follow its natural tendency to expand. A sturdy fence, arbor, trellising, pergola, garden tuteur form--or even a dead tree stump--will provide the surface that the plant tendrils need, in order to grip and climb. Wind the tendrils around and through the support structure as they grow, and affix them loosely with flexible green plant ties if needed.
Prune thunbergia to control its shape and size or to remove damaged or dead vines. Pluck spent flowers to induce fresh bloom, if they do not fall away on their own. If you leave the flowers to dry on the plant, the seeds will dry and self-sow. Cut back your thunbergia after the first frost, in climates where it does not winter over; and compost or discard the foliage.