Ornamental · Polemoniaceae
Cup-and-saucer Vine
Cobaea scandens
Give it full sun and a tall, sturdy support, and this fast climber covers a wall in bell-shaped flowers by late summer.
Full sun
Every 3–7 days
75–120 days
USDA 9–11
Overview
Cup-and-saucer vine earns its name from the flower: a deep bell of a cup sitting on a wide, leafy green saucer of a calyx. The blooms open a creamy green and age to a rich violet-purple, so a single vine shows off both colors at once. It comes from the highlands of Mexico, which is why gardeners in cold regions treat it as a tender plant rather than a perennial.
What sets it apart is sheer speed. Started from seed in late winter, it climbs 10 to 20 feet or more in one season, grabbing onto anything in reach with branched tendrils at the tips of its leaves. Give it a fence, an arbor, or a tall trellis and it will cover the lot by late summer.
It asks for little once it is up and running. The main jobs are a strong support, full sun, and a light hand with feeding, since rich soil and heavy nitrogen leave you with a wall of leaves and few flowers. Get the balance right and it blooms from summer until the first frost.
Care
The short version: full sun, a tall sturdy support, and steady, even moisture in fertile but not over-rich soil, with a light hand on the nitrogen so it flowers instead of running to leaf.
Light
Grow this vine in full sun for the most flowers, though it will take a little afternoon shade. A spot against a warm, sunny wall suits it best, since the extra heat pushes both the growth and the blooms.
Water
Keep the soil evenly moist through the growing season and water regularly while the vine is putting on growth. Don't let it dry out fully in hot weather, but make sure the ground drains well, because it won't sit happily in soggy soil.
Soil
It grows in loam, sand, or clay as long as the drainage is good, across a pH of 5.5 to 7.5. Aim for fertile ground rather than heavily enriched soil, since too much richness pushes leaves at the cost of flowers.
Temperature
The vine handles a wide range, roughly 25°F to 90°F (-4°C to 32°C), but it has no tolerance for hard frost. Treat it as tender and get it outdoors only once the cold has truly passed.
Humidity
Ordinary outdoor humidity is all it needs, so there's no figure to chase. What matters more is air moving through the foliage, which keeps the sap-sucking pests it attracts in check.
Feeding
Feed monthly through spring and summer with a balanced or lower-nitrogen liquid feed. Go easy on the nitrogen, because too much grows a leafy plant that flowers poorly, which is the opposite of what you want.
Pruning
Grown as an annual it barely needs pruning. Pinch the young tips to make it branch and tie the stems onto their support as they climb. Where it lives on as an evergreen, cut it back in late winter to shape it and clear any diseased growth.
Repotting
Pot seedlings up as they grow, then plant them out once the frost has passed. For a container plant, shift it to a bigger pot when the roots fill the old one or start creeping out the drainage holes.
Size & spacing
This is a big climber, reaching 10 to 20 feet (3 to 6 m) in a single season with a spread of 3 to 6 feet (91 to 183 cm). Give it that much room and a support tall enough to hold it.
When to plant
This vine loves warmth and frost ends it cold. Start the seed indoors in late winter, set the young plants out only once the cold has passed and the soil has warmed, and the flowers come from summer right up to the first frost.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Start seed indoors about 8-10 weeks before last frost; sow seeds on edge and keep warm (about 68-72 degrees F), germinating in roughly 14 days.
- Plant: Transplant out after all danger of frost has passed and soil is warm.
- Harvest: Blooms summer into fall until frost; flowers open creamy-green and age to deep violet-purple, each cup sitting on a leafy green calyx saucer.
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Most of what goes wrong with this vine is easy to read and easy to fix. The big ones are a plant that runs to leaf instead of flower, sap-sucking pests on the undersides of the leaves, and stems with nothing to climb. Match what you see below and act early.
Plenty of leaves but few or no flowers
When the vine grows lush and green yet sets almost no buds, the usual culprit is too much nitrogen in the soil or feed, which pushes leaves at the expense of blooms. A short, cool season and too much shade hold it back too. Cut back on nitrogen, move it into full sun against a warm wall, and start the seed earlier indoors to give it a longer run.
Fix:
- Reduce nitrogen and switch to a balanced or lower-nitrogen fertilizer
- Site in full sun against a warm wall or trellis
- Start seed earlier indoors (8-10 weeks before last frost) to lengthen the growing season
Vine flops, tangles, or refuses to climb
This is a climber with branched tendrils at its leaf tips, and it needs something tall and sturdy to grab. Without it, the fast stems sprawl across the ground or smother whatever is nearby. Put up a strong trellis, fence, arbor, or wall before you plant, then guide and loosely tie the young stems on until the tendrils take over.
Fix:
- Install a tall sturdy trellis, fence, arbor, or wall before or at planting
- Guide and loosely tie young stems onto the support until tendrils take hold
Curled, stippled, or yellowing leaves with fine webbing
Sap-sucking pests are at work here. Check the leaf undersides for soft aphids, dust-fine spider mites trailing webbing, or a cloud of whiteflies that lifts when you brush the plant. Knock them off with a hard jet of water, then follow up with insecticidal soap or horticultural oil, coating the undersides where they hide.
Fix:
- Spray off pests with a strong jet of water
- Apply insecticidal soap or horticultural oil, covering leaf undersides
- Repeat treatment and improve air circulation
Toxicity
Good news for households with pets and children: cup-and-saucer vine is not toxic. It doesn't appear on the ASPCA's poison lists, and no poisoning has been reported in animals or people, so you can grow it over a fence or arbor without worry. It is grown for show, not for eating.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to grow around cats. A nibbling cat may get a mildly upset stomach from any unfamiliar greenery, but no toxin in this vine poses a real threat.
Dogs None
No toxicity is documented for dogs. A dog that chews a stem or leaf is in no danger, though a big mouthful of any plant can briefly loosen the stomach.
Horses Safe
Considered safe for horses, with nothing on record to suggest the foliage causes harm if a grazing horse takes a taste.
Rabbits Safe
Rabbits can be around this vine without worry. None of its parts carry a toxin known to trouble them.
Livestock Safe
No poisoning has been reported in cattle, goats, or sheep, so the plant is regarded as safe near grazing stock.
Birds Safe
Safe around birds, whether pet or backyard. The leaves and flowers hold no compound flagged as toxic to them.
People Safe
Not toxic to people, and curious children are in no danger from a stray leaf or flower, though it is grown for show rather than the table.
No special handling required; wash hands after gardening as a general practice.
Varieties
The straight species shifts from green to purple as its flowers age, but a few named selections lock in one color. These are the ones worth knowing.
'Alba'
A white-flowered form whose cups stay creamy-white rather than aging to the usual violet-purple.
'Key Lime'
Grown for its flowers, which hold a fresh green to chartreuse lime coloring instead of turning purple.
'Royal Plum'
Carries rich, deep purple flowers for gardeners who want the darkest color the vine offers.
How to propagate
You can raise cup-and-saucer vine from seed for plenty of plants, or take cuttings when you want to keep a particular color true.
SeedEasy
Start indoors 8-10 weeks before last frost; transplant out after frost. · Germinates in about 14 days at 68-72 degrees F; can be slow to start, then grows rapidly.
Most gardeners raise this vine from seed. Sow it on edge and keep the tray warm, around 68°F to 72°F (20°C to 22°C), starting 8 to 10 weeks before your last frost. Germination is slow and takes about 14 days, but once the seedlings catch they grow fast, so move them outside only after the frost has passed.
Stem cuttingsModerate
Spring or summer during active growth · Several weeks to root
Take softwood cuttings in spring or summer while the vine is growing hard. This is the way to copy a named selection true, since seed won't always hold the color, and the cuttings need several weeks to root before they're ready to plant on.
Myths
This exotic, tropical-looking vine must be hard and slow to grow.
The showy bell-shaped blooms make it look fussy, but it is easy and very fast from seed, climbing 10 to 20 feet or more in a single season. In cold climates you simply grow it as a warm-season annual and start over each spring.