Tender climbers
Joan Millard

I often think that our name ‘Hardy Plant Society’ is a misnomer. Hardiness of plants has shifted the boundaries somewhat over the past few years and we are able to grow plants outside all year, which used to be termed half-hardy and needed winter protection. Of course there is always the exception, as we found with the very severe winter of 2008/9. There were certainly a few casualties then. Most of us are interested in tender as well as hardy plants, if not great fans of the ‘bedding varieties’. The plants which I want to talk about are definitely of the very tender type but, to my mind, well worth the extra trouble they require for their glorious displays all summer long.

Each year in March I try sowing a few tender climbers in seed trays. They need to be sown in a warm place, preferably in a heated propagator to get them started. Seeds which I have been successful with include ipomoea (morning glory), thunbergia (black-eyed Susan), cobaea (cup and saucer plant) and rhodochiton (purple bell vine). Ipomoea always germinate easily and rapidly and so could be left until late March for propagation. The others I find more variable for germination, some taking several weeks and some, in my own experience, Eccremocarpus scaber in particular, never making it.

When the seedlings are a couple of centimetres high they need to be pricked out into larger pots, I normally plant three to a 9 cm pot. They still need to be kept warm, a south facing windowsill is ideal, so long as they are moved at night if there is any chance of cold. In the case of Cobaea scandens it is recommended that each seed is placed into a separate pot from the start, probably to avoid early disturbance. This particular plant I found difficult to germinate, even though I waited for the recommended 28 days. It seemed that the seeds rotted before germination – any ideas on avoiding this? In the end, after two or three attempts I raised three seedlings! Unfortunately only one of these came to full fruition once planted out. It went straight into garden soil on a trellis along with sweet peas, but what a strong, prolific plant it was, bearing many of those lovely ‘cup and saucer’ flowers. Each large flower is a subtle mix of cream, pale purple, through to a deeper purple. One needs to get an eye in as it is not easy to spot, but what a delight once seen! The ‘cup’ falls away in time, leaving the pale green calyx or ‘saucer’ which stays on the plant. Since this plant was a late starter, unfortunately I did not get any ripened seed from it.

Once potted on the seedlings will probably grow apace and need to be supported by small sticks so that they can twine around. This is where the fight to keep up with growth starts in earnest. Once they get into their stride, most climbers vigorously do what they are meant to do, that is, climb. Unless watched carefully they can get out of control and twine around anything that comes to hand, the next plant’s support, the standard lamp, the furniture, etc. They reach out with their tips for any contact they can find. I find the best approach once they get to this stage is to plant each pot-full, with as little disturbance as possible, into a larger, permanent pot, 30-33 cm diameter is ideal. Each large pot could take up to half-a-dozen small pots if desired or two or three into a slightly smaller pot, still large enough to take tall supports. At the same time incorporate an obelisk into the pot, a light bought one or one made with bamboo canes, making sure that it is not too high to move through the outside doorframe when the time comes. It is tempting to use decorative terra-cotta or ceramic pots but bear in mind the weight for moving around. I have settled for plastic after straining the back in previous years. Of course, you must have room somewhere light and warmish to accommodate these large pots. My conservatory is ideal for this, even if it means that we are peering through foliage until such time as the pots can be moved outside. Of course, this cannot happen until there is no danger of frost. I normally reckon on the first week of June. The pots are then moved outside to positions where there is further support for them to climb, or onto a sunny patio with just the support of a wigwam-like frame. I find that plants do better if left in their pots rather than planted into the soil as watering is more easily controlled.

The easiest climbers to grow are the ipomoeas, each flower lasting for just a day, to be replaced by many more the next day. Nothing like its thuggish cousin, the wild columbine, ipomoea comes in colours from sky blue, blues through to purples and even crimson. They need a warm, sunny summer to perform at their best. Even then they are rarely as prolific as those we see in Mediterranean climes. However, they can give a good show and will go on flowering until late September if the weather holds. I sometimes find that they have more leaf than desirable for the amount of flower but this is probably due to wet conditions. Ideally they need to be planted where there is plenty of room to climb as they can cover large areas. Mine were kept in their 33 cm pot against a fence which also had honeysuckle growing along it and looked amazing intermingling.

Another variety of ipomoea is I. lobata, which was previously called Mina lobata. Although this is the same genus as the previous plant, it has an altogether different, more delicate appearance. Still very prolific, the flowers are borne in small one-sided, tubular red and yellow racemes. Give this climber plenty of height, perhaps next to a trellis and it will climb ever higher all summer.

The length of flowering for these climbers varies with the plant and with weather conditions. Most like it hot but also require sufficient water. By starting them off early indoors, they bloom earlier and will often last until the weather cools in autumn. Hopefully they will produce seed for collection and sowing next year but sometimes with a poor summer this does not happen.

First published in the Berkshire Group Newsletter, January 2010
and subsequently in Cornucopia Issue 27.
© Copyright for this article: Joan Millard

This article was taken from a copy of Cornucopia that was published in 2011. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.