Cup and saucer vine (Cobaea scandens) is perennial climber native to subtropic regions. It features purple flowers that are unexpectedly muted. The common names for C. scandens—"cup and saucer" and "cathedral bells"—derive from the shape of its flowers. This is a vigorous vine that is hard to ignore in the landscape. Although C. scandens takes awhile to start blooming, the foliage will quickly make itself at home and create a screen or cover.
The plant has plentiful bright green leaves, oblong in shape. The cup-shaped flowers are pale green as they start to open, but quickly turn purple or white as they fill out. The opening buds have a somewhat unpleasant scent, but the fully opened flowers develop a floral-honey fragrance. The green calyx remains at the base of the flower and becomes the saucer.
|Botanical Name||Cobaea scandens|
|Common Names||Cup and saucer vine, cathedral bells, monastery vine|
|Plant Type||Perennial vine, usually grown as an annual|
|Mature Size||10 to 20 feet; 3- to 6-foot spread|
|Sun Exposure||Full sun|
|Soil Type||Medium moisture, well-drained soil|
|Soil pH||No preference|
|Bloom Time||Seasonal bloomer|
|Flower Color||Green, maturing to purple|
|Hardiness Zones||9 to 11; grown as an annual elsewhere|
|Native Area||Mexico, parts of Peru|
How to Grow Cup and Saucer Vine
Cup and saucer vine grows so quickly that it is usually started from seeds rather than from nursery plants. You can direct seed in the garden after all danger of frost is past, or get a head start by starting seeds indoors 6 to 8 weeks before your last frost of the winter/spring.
The seeds are large, flat, and tough. Soaking them in water the night before planting seems to help speed germination. Germination can be erratic, but you should see sprouts within 2 to 4 weeks. Since the vines will get entangled, you should start them in separate pots filled with ordinary potting mix. You will also find it helpful to insert a twiggy trellis immediately to keep them under control right from the start.
When planting, tuck the flat seeds into the soil vertically, with the longest edge facing down, and barely cover with soil. Don't worry too much about positioning the seeds perfectly, but placing them flat and covering them with soil can cause them to rot. The seeds prefer warm soil (70 to 75 degrees Fahrenheit.) If starting indoors, heat mats or placing the seed trays on top of the refrigerator will accomplish this.
If planting the seeds outdoors, be aware that young cup and saucer vine plants are sensitive to the cold. Give them some protection if the temperature dips. Start training the vines early and they'll take it from there. To control the size, pinch off the stems when they reach the top of your support or eye level. This will encourage branching and bud set. There is no need to deadhead the flowers.
Cup and saucer vine can attract aphids, especially when the plants are young and succulent. Frequent blasts of water or a couple of treatments of insecticidal soap should control them. Older plants can fall prey to spider mites, especially during dry weather. Again, hosing down the plants will help control the pests.
It is said that this flower is pollinated mostly by bats when grown south of zone 7. These flying mammals are generally harmless, and even helpful for controlling insects, but if the idea of bats flitting around your garden disturbs you, you may want to avoid this plant.
This vine needs full sun to bloom well.
Cup and saucer vine is not particular about soil pH, and it grows well in any well-drained soil. It does not need rich soil, although some organic matter will keep it growing and blooming without additional fertilizer.
Keep the vines watered regularly, but don't let the soil remain wet.
Temperature and Humidity
As a summer annual, this vine grows well in just about any growing zone—even Alaska. If grown as a perennial, it will be reliably hardy in zones 10 and 11, but may die off in zone 9.
Go easy on the fertilizer, or you will get a lot of vine growth and few flowers. If necessary, side-dress with compost in mid-summer.
Propagating Cup and Saucer Vine
Cup and saucer vine will readily self-seed, and the seedlings can be transplanted into other locations. The seeds can also be collected for planting wherever you choose. This plant self-seeds very readily, so be aware that it may become invasive under some conditions.
Varieties of Cup and Saucer Vine
It is the native purple-flowering species that is normally grown in gardens, but there is also a white-flowering form, C. scandens f. alba.
This sprawling vine can engulf nearby plants. Use cup and saucer vine when you want a solid cover, or to screen a fence, wall, or ugly view. You can grow it in containers, but you'll need a large one, and it will need to be weighted to hold the weight of the vine and whatever support you include for it.
If you'd like color earlier in the season, you can plant other annual flowering vines as companions.
Smith, Miranda. Gardening: the Complete Guide. Creative Homeowner, 2012
Fell, Derek. Vertical Gardening: Grow up, Not out, for More Vegetables and Flowers in Much Less Space. Rodale, 2011