Ornamental · Polemoniaceae
Cup-and-saucer Vine
Cobaea scandens
Hand it full sun and a tall, sturdy support, and this fast climber will drape a wall in bell-shaped flowers by late summer.
Full sun
Every 3–7 days
75–120 days
USDA 9–11
Overview
So where does the name come from? The flower, of course: a deep bell of a cup that sits right on a wide, leafy green saucer of a calyx. The blooms start out a creamy green and slowly turn a rich violet-purple, which means one vine often shows both colors together. It's from the highlands of Mexico, and that's exactly why folks in colder spots grow it as a tender plant instead of a perennial.
The real headline here is speed. Start it from seed in late winter and it'll climb 10 to 20 feet or more in one season, grabbing whatever's nearby with those branched tendrils at the tips of its leaves. Give it a fence, an arbor, or a tall trellis, and it'll cover the whole thing by late summer.
Once it's up and going, it doesn't ask for much. What it really wants is a strong support, full sun, and a light touch with the feeding, because rich soil and heavy nitrogen just leave you with loads of leaves and hardly any flowers. Get that balance right, though, and it'll bloom 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, and go light on the nitrogen so it spends its energy on flowers instead of leaves.
Light
Give this vine full sun if you want the most flowers, though it'll put up with a little afternoon shade. A spot against a warm, sunny wall is just about perfect, since that extra heat gets both the growth and the blooms going.
Water
Keep the soil evenly moist all through the growing season and water regularly while it's putting on new growth. Don't let it dry out completely when it's hot, but make sure the ground drains well, because it won't be happy sitting in soggy soil.
Soil
It's happy in loam, sand, or clay as long as the drainage is decent, anywhere across a pH of 5.5 to 7.5. Go for fertile ground rather than super-rich soil, since too much richness pushes leaves and skimps on flowers.
Temperature
It copes with a wide range, roughly 25°F to 90°F (-4°C to 32°C), but it just can't handle a hard frost. Treat it as tender and only move it outside once the cold has properly gone.
Humidity
Regular outdoor humidity is all it needs, so there's no number you have to hit. What matters more is air moving through the leaves, which helps keep those sap-suckers it attracts under control.
Feeding
Feed it 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 barely flowers, which is the opposite of what you're after.
Pruning
Grown as an annual, it hardly needs any pruning. Pinch the young tips to get it branching, and tie the stems to their support as they head up. Where it lives on as an evergreen, cut it back in late winter to tidy the shape and clear out any diseased bits.
Repotting
Pot the seedlings up as they grow, then plant them out once the frost has passed. If it's in a container, move it to a bigger pot when the roots fill the old one or start poking out the drainage holes.
Size & spacing
This is a big climber, getting up to 10 to 20 feet (3 to 6 m) in just one season with a spread of 3 to 6 feet (91 to 183 cm). Give it that much room and a support tall enough to take it.
When to plant
Here's the thing: this vine loves warmth, and a cold snap is what finishes it off. Start your seed indoors in late winter, only set the young plants out once the cold has passed and the soil's warmed up, and you'll get flowers from summer right through 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 pretty easy to spot and easy to sort out. The usual suspects? A plant that's all leaves and no flowers, little sap-suckers hiding under the leaves, and stems with nothing to climb. Find the match below and jump on it early.
Plenty of leaves but where are the flowers?
Got a big green vine and barely a bloom in sight? Usually that's too much nitrogen talking, since it tells the plant to make leaves and skip the flowers. A short, cool season or too much shade can hold it back too. So ease off the nitrogen, move it into full sun by a warm wall, and start your seed a bit earlier indoors next year to give it more time.
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 flopping over instead of climbing?
If it's sprawling around rather than heading up, it just hasn't found anything to grab. This one climbs with branched tendrils at the tips of its leaves, and it really wants something tall and solid to hold onto. Give it nothing and those quick stems will wander across the ground or pile onto whatever's next door. Put up a sturdy trellis, fence, arbor, or wall before you plant, then guide and loosely tie the young stems until the tendrils get the hang of it.
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
Leaves curling, speckled, or yellowing with a bit of webbing
When leaves curl up, get speckled, or turn yellow, there's a good chance tiny sap-suckers have moved in. Flip a leaf over and you'll often spot soft aphids, dust-sized spider mites with their fine webbing, or whiteflies that puff up into a little cloud when you nudge the plant. A strong blast of water knocks loads of them off, and then insecticidal soap or horticultural oil on the undersides handles the stragglers.
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 if you've got pets or kids running around: cup-and-saucer vine is not toxic. It doesn't show up on the ASPCA's poison lists, and there's no record of it poisoning animals or people, so you can let it cover a fence or arbor and not give it a second thought. It's grown for looks, not for the dinner table.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Cats are fine around it. If one decides to nibble, it might get a slightly upset stomach the way any new leaf can do, but there's no toxin here that'll actually hurt it.
Dogs None
Nothing toxic for dogs to worry about. A dog that chews on a stem or leaf isn't in any danger, though wolfing down a big mouthful of any plant can leave the stomach a little loose.
Horses Safe
Horses are good with it, and there's nothing on record saying the leaves cause trouble if a grazing horse grabs a taste.
Rabbits Safe
Rabbits can hang around it just fine, because none of its parts carry a toxin that's known to bother them.
Livestock Safe
No poisoning's ever been reported in cattle, goats, or sheep, so it's considered safe to have near grazing animals.
Birds Safe
Birds are safe with it too, whether they're pets or just visiting the yard, since the leaves and flowers don't hold anything flagged as toxic to them.
People Safe
It's not toxic to people, so a curious kid who grabs a stray leaf or flower is in no danger, though it's really grown for the show rather than for eating.
No special handling required; wash hands after gardening as a general practice.
Varieties
The plain species shifts from green to purple as the flowers get older, but a few named picks stick to just one color. These are the ones worth knowing about.
'Alba'
This is the white one, with cups that stay a soft creamy-white instead of deepening into the usual violet-purple.
'Key Lime'
Here the flowers keep a fresh green to chartreuse lime color rather than going purple as they age.
'Royal Plum'
If you're after the moodiest color, this one brings the richest, deepest purple the vine can manage.
How to propagate
Want a bunch of plants? Grow cup-and-saucer vine from seed. Want to hold onto one particular color? Take cuttings instead.
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.
Seed's the way most folks grow this vine, and it's the easy route. Pop each seed in on its edge, keep the tray nice and warm at 68°F to 72°F (20°C to 22°C), and get going 8 to 10 weeks before your last frost. It's a bit slow to sprout, around 14 days, but once those seedlings wake up they really take off, so hold off planting them out until the frost is well and truly gone.
Stem cuttingsModerate
Spring or summer during active growth · Several weeks to root
Fallen for a certain color? Take softwood cuttings in spring or summer while the vine's growing hard, because that's how you copy a named selection exactly, and seed won't always keep the color true. Just give the cuttings several weeks to root before you plant them on.
Myths
A tropical-looking vine like this has got to be hard and slow to grow.
Sure, those big bell flowers make it look like a handful, but it's actually easy and seriously fast from seed, climbing 10 to 20 feet or more in just one season. If your winters are cold, you just grow it as a warm-season annual and start fresh again come spring.