The cup and saucer plant (Cobaea scandens) is also called Cathedral Bells. It is originally from Mexico. It is a perennial vine that is treated as an annual in cool climates. It grows as a perennial in zones nine to eleven. Leaves are dark green and alternate with three pairs of leaves. At the end of the branch is a tendril to use to hold it to the object it is climbing. Large flowers on long slender stems start out as green then develop into a deep purple. The cup and saucer plant can grow to around twenty feet in a season. It spreads three to six feet. The flowers occur in late summer and early fall.
The cup and saucer plant needs to be planted in full sun. It appreciates some shade in the afternoon in hot climates. Cup and saucer needs well-drained, fertile soil. To achieve that, till the area where you are planting the plant to a depth of six inches. Add three inches of compost, then till that in until it is spread throughout the soil. The compost adds fertilizer to the soil and also helps keep water from pooling around the plant. Cup and saucer does not like wet feet. The soil must be kept moist but not soggy or the cup and saucer plant will get root rot.
Cup and saucer is propagated by seed. It should be started inside eight to ten weeks before the last frost. Cup and saucer plants are difficult to germinate. Fill four inch peat pots with a sterile potting medium. Nick the long side of the side with a knife. Plant the seeds with the longest edge down. Barely cover the seeds with the potting medium. Use a heating mat to keep the soil temperature 70 to 75 degrees F. Germination takes ten to fourteen days. Plant more plants than you want to have because the seeds are hard to get to germinate.
When you are ready to transplant your cup and saucer plants, you will need to harden them off first so they do not die when put outside. Place the peat pots with the cup and saucer plants in a sheltered area where they get plenty of sun. Leave them out for two or three hours then bring them back in. Over a week’s time, gradually lengthen the time the pots are outside until they are outside all day. Now they are ready to transplant. Leave them in their peat pots and plant them 24 to 36 inches apart. Water well after you transplant the plants.
If you do not want to start the cup and saucer plants inside, you may sow them outside after all danger of frost has past. Sow them on prepared ground near a trellis or wall they can climb. Barely cover them with soil after you sow the seeds. The seeds will germinate in ten to fourteen days. The flowers will be delayed until early fall if you use this method of planting them.