How to Grow Cobaea Scandens From Seed

Cobaea scandens, sometimes known by the common names of the “Cup and Saucer Vine” or “Cathedral Bells”, is a stunning climbing plant that can be easily grown from seed. 

Cobaea scandens is half-hardy, meaning that in most temperate areas the vines will die over winter. As a result, to maintain an attractive display it is normally necessary to grow new Cobaea scandens plants from seed every year.

Fortunately Cobaea scandens is a reasonably easy plant to grow. In this article I’ll discuss my own experiences of growing Cobaea scandens from seed, which is something that anyone with a little spare space can accomplish. 

Warning: Cobaea scandens seeds are poisonous. When trying to grow Cobaea scandens from seed be sure to take suitable precautions. Use gloves or wash your hands when coming into contact with the seeds and suitably protect children and pets. 

How Do You Plant Cobaea Scandens Seeds?

In my experience Cobaea scandens germinates very readily, which is a real benefit for the passionate gardener. Unlike some other seeds that either require careful preparation or huge amounts of patience it seems Cobaea scandens germinate easily and quickly when given the right conditions. So what are these conditions?

Select a Large Plastic Flower Pot

Cobaea scandens grows surprisingly quickly once it gets going. What’s more, as a vine it’s tendrils will grab onto anything placed near the pot. Planting lots of Cobaea scandens seeds in a single small container can lead to a real mess some weeks down the line as they will have all plaited together into an uncontrollable mess.

In my experience a better option is to place individual seeds into individual pots. This way they can be kept separate and their growth can be easily controlled by moving around the pots as necessary. 

Due to the speed of growth I recommend a pot of at least 6” for each seed. While I appreciate that not all seeds will germinate, this does mean that those that do can be easily managed. 

The rate of growth means that smaller pots can be quickly overwhelmed, requiring regular repotting. While repotting isn’t the end of the world, it does add to the effort required to grow Cobaea scandens while also risking damaging the seedlings themselves. 

Fill the Pot With Multipurpose Compost

Cobaea scandens does well in rich, free-draining multipurpose compost. I choose a peat-free option for it’s environmental benefits. Fill up the chosen plant pot to around an inch from the top and gently firm down. 

You may wish to water the pot at this point, or leave until the seeds themselves have been planted – both options will work just fine. 

Gently Position the Seeds

Place the seeds onto the surface of the compost, one per pot. 

Cover With Compost Twice the Depth of the Seed

Cobaea scandens does not need light to germinate so feel free to well-cover the seeds. They like moist conditions to germinate so a decent covering of compost can help to keep the seeds damp in their sensitive early days of growth. 

Water Thoroughly

You want the compost to be moist without being sodden. Possibly the easiest way to achieve this is to place the pots into a tray of lukewarm water. The compost will then soak up all the water necessary. Half an hour should do it. 

Remove the pots and place them to one side so any excess water can drain away. At this point you’re ready to move on to the next step.

Place into a Plastic Bag

To maintain a moist growing environment I like to cover the pots. If you have clear plastic bags big enough then place the entire pot inside. If not I simply lay clear plastic over the top of the pot and fix in place with masking tape. Masking tape works well as it remains “sticky” so it is easy to peel back the plastic to check on your Cobaea scandens seeds, then replace it afterwards. 

Place in a Warm Room

Lastly, and most crucially, Cobaea scandens seeds need warmth to germinate successfully. Place them on a warm south-facing windowsill in your house or into a heated propagator. A temperature of 20-25’C is ideal for the germination of Cobaea scandens.

Now all you need to do is cross your fingers and wait. Check the pots regularly and, if necessary, spray on a little more water from a houseplant mister to keep the soil moist at all times.

How Long Do Cup and Saucer Vine Seeds Take to Germinate?

Cup and Saucer Vines tend to be very quick to germinate. It can take as little a week for seedlings to start showing their heads, though if it takes a little longer then you shouldn’t worry too much.

Each spring I plant a whole host of seeds – including both flowers and vegetables – and almost without exception my Cup and Saucer vine seeds are some of the first to germinate. 

Bearing in mind the rate of growth once they have germinated this means you’ll need to be ready for them when they appear! 

When to Plant Cobaea scandens Seeds

Cobaea scandens is normally grown as an annual. While it grows as a perennial in its native country, snow and frost will normally kill Cobaea scandens in temperate regions. 

This means that the best time to plant Cobaea scandens seeds is in early spring. This gives the plant time to get established before the best of the weather appears, and gives a long flowering season. 

Once Cobaea scandens starts flowering it will continue to do so almost non-stop till killed by winter temperatures. This means that the sooner you start your plants the longer the flowering season you will enjoy. 

Depending on when the last frosts are in your region Cobaea scandens seeds are best planted between March and May. Even seeds planted later may still have enough time to flower when given the ideal growing conditions. 

Caring for Cobaea Scandens Seedlings

Cobaea scandens seedlings grow surprisingly rapidly. Fortunately they need little in the way of specialist care. Put simply, they like a warm and sunny position, be that a windowsill or a greenhouse. They also appreciate generous watering, though avoid water-logged conditions at all costs. 

The trick is really keeping your Cobaea scandens seedlings in the best of health until the last frosts have passed, which could be as late as May in some parts. As a climber it can be worth giving them some support to grow up. This prevents them falling over and attempting to latch onto other plants. 

A frame is easy enough to construct with a few pieces of garden cane and a few cable-ties. 

Once you’re confident that the last frosts have passed they can be planted out in their final flowering position. Mine do best when grown up a south-facing fence, where the timber of the fence naturally creates a warm little microclimate, and they are bathed in sunshine all day long. 

When planted out, as when grown in pots, be sure to give your Cobaea scandens some support. Try growing them up a trellis or a plant net to ensure they have something to attach their tendrils to. 

Why Is My Cobaea Scandens Not Flowering?

Cobaea scandens is normally quite free-flowering. Once your Cobaea scandens plant starts to flower it will likely continue to do long after most other plants have finished. My Cobaea scandens vines are often still in flower in September, October and even November when the weather has been reasonably mild. 

If your Cobaea scandens is not flowering then there can be a number of things worth considering…

Age/Size

Cobaea scandens takes some time to reach “flowering size”. Start seeds early in the spring and it still might be late summer before the plants are big enough to start flowering. If you’re worried that your Cobaea scandens isn’t flowering in May or June it may simply be a case that you need to be a little more patient yet – don’t give up hope!

Sunshine Levels

Cobaea scandens appreciates a sunny position. When I compare the specimens grown against the south side of my fence with those on the east-facing side there is little doubt that those getting the most sunlight grow faster and more vigorously.

If you’re concerned that your Cobaea scandens isn’t flowering then it might be worth considering if there are any other nearby plants that you could prune back to maximise the sunlight reaching the leaves of your Cobaea scandens.

Temperature

Cobaea scandens like a warm environment. It doesn’t have to be tropical, but the warmer the better. 

This is all well and good, but it means that the results can vary year-to-year for those of us living in temperate regions. A notably cool or wet summer can mean that your Cobaea scandens never reaches it’s potential. 

In contrast, reliably warm and sunny summers can see your Cobaea scandens absolutely covered in flowers. 

If in doubt try planting Cobaea scandens where it will get lots of sunshine – and therefore warmth. Planting them against a wall or fence can also help to increase the temperature for your plant. 

Nutrient Provision

Having grown Cobaea scandens in all sorts of areas around my garden my results demonstrate that Cobaea scandens seems to do best when it is grown in rich soil with lots of nutrients. If your Cobaea scandens won’t flower then consider adding some fresh compost or fertilizer around it’s roots and water in well to release these nutrients. 

Watering

While Cobaea scandens doesn’t seem to like boggy conditions, it does use a considerable amount of water to put on such a growth spurt. In hot summer weather it can be worth watering your Cobaea scandens daily, if not more than once a day, to ensure it has all the water it needs.

Cobaea scandens Seed Pods & Collecting Seeds

While Cobaea scandens is normally propagated from seed, there is no denying that Cobaea scandens seed tends to be rather expensive. 

Cobaea scandens flowers readily, however getting fertile seeds from your garden-grown plants can be next to impossible. A vine that has been covered in flowers for months on end will still typically fail to produce any fertile seeds. 

The issue seems to be a lack of fertilization. There have been suggestions that Cobaea scandens flowers may naturally be pollinated by bats or other animals not present in our temperate region. 

Some growers claim the only way to succeed with producing and gathering Cobaea scandens seeds is to manually pollinate the flowers. To do this use a soft paintbrush, gently moving from one open flower to the next, and repeating the process regularly throughout the season. If you’re lucky, some pollination will occur and you might just end up with some Cobaea scandens seeds to collect.

In truth, for most of us, it’s unlikely we’ll ever produce our own Cobaea scandens seeds, so it’ll probably be necessary to just buy some more from your favourite seed supplier next spring. 

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