How to overwinter pelargoniums
When I started gardening, pelargoniums were grown from cuttings and it was an annual ritual to dig up, dry off and save the plants or to take cuttings in August to keep them for the following season. All that changed when plant breeders produced reliable, colourful strains that would flower well the first year from seed. Many of the plants you buy in late spring will be grown from seed but more will be grown from cuttings, produced in vast numbers by commercial nurseries. The cuttings are sent to local nurseries that grow them on ready for sale in May and June. It has to be said that all these new kinds are compact, short-jointed and usually have large, double flowers. But I still prefer some of the older kinds which are more vigorous and, to my eyes, have more character and appeal.
Pelargoniums can withstand cold winter temperatures, down to almost 0c, if they are dry. Cold and damp is the real problem. There are several, traditional ways to keep them over winter. If you are content to suffer pots on house windowsills you can pot them in autumn and the plants will continue to grow and bloom all winter, depending on temperature. In very sheltered areas, in towns and cities and by the coast, pelargoniums may survive the winter outside.
The old-fashioned way to overwinter plants, if you are nor able to pot them and keep them in a frost-free greenhouse, is to lift them in autumn, lay them out to dry and then store them, dry, over winter. Now this is pretty brutal and not all plants will survive. Some varieties won’t put up with this, but more vigorous kinds may. The plants are allowed to dry out, so that most leaves drop off and then the plants are wrapped in newspaper, or stuffed in boxes with some straw of even hung up in a shed. In spring, the plants will look awful but can then be potted, cut back and started into growth again. you can then take cuttings of the new shoots, if desired. What is absolutely essential is that the plants are NOT cut back in autumn. Any pruning cuts will start to rot and the stems die back. Fungal black rot or grey mould will spread down the stems and kill the plants.
A better way to maintain your stock is to take cuttings in August. These should root quickly and the young plants take up minimal space in the greenhouse or on the windowsill during winter and they can be potted in spring and make good plants to put out in May. Depending on the variety, if these are well rooted, they will survive low temperatures, close to 0c. My plants (below) have survived a cold greenhouse that did drop to just below 0c and damaged a few other plants but not the pelargoniums. There is a balancing act between keeping the young cuttings dry and moist enough to keep them just ticking-over.
Winter in the greenhouse is always a dilemma. We keep it closed to keep it as warm as possible and to maintain any heat we provide, but we must ventilate it whenever possible or moisture levels rise and grey mould becomes a problem (below). Pick over the plants regularly and always remove any mouldy leaves as soon as you can. On sunny, dry days, let some fresh air in to reduce fungal problems.
A greenhouse in winter is also a perfect place for pests to shelter from the weather. The young leaves on the pelargoniums above are showing slight curling which is a sure sign that aphids are present. The dilemma here is whether to spray or not. I don’t want to wet the leaves any more than necessary so I will just go over the plants and squash the pests.
Yes, they are a challenge!
It is annoying that if ours get frosted, they seem to do so early in the season, necessitating cutting them back prematurely. They live in the ground outside all year, since they do not need the protection of a greenhouse, but do not have enough sense to lay low through winter. They regenerate new growth just fine, but it is a bit stretched, and can get tattered from winter storms, such as those that are in the news now. If ignored and not pruned back, their new growth can partially rot below the old growth like it does in a greenhouse in other climates, except that it is under old growth. Even if they do not rot, and do not get frosted, the old growth must still get cut back without damaging the new growth. It seems to be almost as complicated as just taking new cuttings annually.
That does sound complicated. But they are so colourful, for so long, that they are worth a bit of effort.
Well, if all else fails, I can cut them back and get them to start over. I hate to cut back new growth, but have done it before.