How to grow specialist campanulas
There is an ever-increasing range of campanula, from robust rock garden species to tall border perennials and some tender perennials. Here we look at how to grow the more specialist types, mainly focusing on alpines and tender species.
- Long-flowering display, blooming during spring and summer
- Variety of habits from mat-forming, dwarf perennials to herbaceous species
- Some thrive on a sunny wall or bank while others enjoy a scree bed or trough
- Tender species need the shelter of a greenhouse from early winter to spring
- Most will not tolerate winter wet
- Some specialist types are evergreen (lose their leaves in winter)
- Take cuttings in early summer
All you need to know
Choosing specialist campanula
There’s a few specialist campanula that are fairly easy to grow with a few extra growing tips so, when selecting the right one for you, it helps to bear in mind the following things:
- These campanula can be quite small or low growing – 5-30cm (2in-1ft) – so are ideal to grow in shallow containers or at the front of a sharply drained border
- Flower colour is mostly pale blues, pale sapphires, purples and whites. Choose a shade that you like and works with the plants you plan to put it next to
- Deciduous types (those that lose their leaves) are the toughest, hardiest campanula. However, some campanula are tender (mainly the evergreen types) and these are best overwintered in a cool conservatory or greenhouse
- The more unusual campanula have pendent bell to funnel or star-shaped blooms and can be solitary, in onesided racemes or have spreading stems
- Go for campanula that have received the RHS Award of Garden Merit as these have been tested by the RHS in trials and perform well in average garden conditions
- Buy hardy types ideally in early spring. You can buy tender evergreen types at this time too, but you will need to protect them from frost
- You can buy potted plants in flower in summer, but be prepared to keep them watered for the rest of the summer so they establish well
To find campanula that are available to buy near you, or to find a specific plant, use RHS Find a Plant
You can grow all specialist campanula in well-drained gritty soil, in full sun or light shade.
For the front of a border, ideally plant your specialist campanula in spring when the risk of heavy frosts are over (mid to late April). If you are going to grow them in containers, plant at the same level that they are in the current pot.
In their natural habitat, specialist campanula often enjoy the winter protection of deep, dry snow and won't tolerate winter wet. If your soil is not free-draining an option is to grow them in a scree garden, in tufa rock, in gritty, sharply-drained soil in a sink or trough or in a container of loam-based potting compost (John Innes No.1) mixed with up to one-third by volume of grit.
There are a few tender campanula that will need to be overwintered in a conservatory or a cool greenhouse with a minimum night temperature of 5°C (41°F) through the winter months, as they are not frost hardy. They need good light levels and ventilation. Grow these in containers, planting them in a mixture of two-thirds loam-based potting compost (John Innes No.2) with one-third grit or perlite.
WateringYou need to water regularly in the growing season, especially in the first year after planting, aiming to keep the soil moist but not soggy. Once established they will need little watering but, during dry periods in spring and summer, paying extra attention to watering will help the plants flower well and resist disease.
You can feed border plants in spring when you start to see some growth. Use a general-purpose fertiliser, such as Growmore or Vitax Q4 according to the manufacturer's instructions.
For containers, you can use a liquid fertiliser monthly from April, such as Phostrogen or seaweed feed, diluting according to the instructions.
Protect your potted plants in autumn by placing in a light, frost-free place, sheltered from the worst of the winter rains. This might be a cool greenhouse or a coldframe if you live in a cold area, but place at the bottom of a south- or west-facing wall if they are hardy and will stay outdoors.
Evergreen plants and the more tender varieties do need winter protection. You can grow these tender types in containers and moved to a frost-free greenhouse or conservatory for the winter.
You don't need to do much in the way of maintenance other than deadheading individual flowers or cutting off the whole flower spike once the blooms have faded. This will encourage plants to repeat flower and keeps the plants tidy.
Once plants have established – after about three years – you can dig them up and divide into smaller clumps. This is the best way to make more plants of a cultivar as all the new clumps will be exactly the same.
You can propagate species campanula by seed sown in containers and placed in a coldframe in spring. Alpine species should be sown in an open frame in autumn so that the cold weather helps breaks seed dormancy and so encourages germination.
Take tip cuttings from tender species such as C. isophylla in early spring and root with bottom heat by using an electric propagator.
Rust diseases and powdery mildews can be a problem for campanula in soils that easily dry out.
If you are a member of the RHS, you can use our online Gardening Advice service.
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