The name Lobelia conjures up for most gardeners an image of dark blue flowers spilling over the edge of window boxes. But it is actually a large and diverse genus, including perennials for the herbaceous border and even trees, in addition to those grown as annuals for summer bedding.
The latter derive from the southern African species L. erinus, which has deep blue flowers, but breeding has led to the colour range being extended to include reds, pinks, whites and pale lilacs. These summer flowering bedding plants are commonly used to edge borders and in containers, with the trailing kinds especially popular in hanging baskets.
There are also some fantastic herbaceous perennials, with tall spikes of strongly-coloured flowers. For example, L. cardinalis Award of Garden Merit (AGM), L. siphilitica and the felty-leaved L. tupa, which are hardy to at least -10 degsC, and the vigorous hybrids, L. x speciosa, which will survive down to -30 degsC.
New growth may appear during warm spells in winter, which is then susceptible to frost. Winter mulch of leaf mould or straw can provide protection against this. In areas that see harsh winters, the tender species such as L. tupa should be lifted and overwintered in cold frames.
Lobelia should be grown in full sun or light shade in an open position, with some shelter from wind. They can cope with ordinary garden soil but prefer being planted in moist, humus-rich conditions. The bedding plants are raised from seed or cuttings and treated as half-hardy annuals, grown in the greenhouse until planting time when the danger of frost is past. Young plants should be pinched out at around 3cm high to encourage bushiness. Once planted, they will need a thorough watering in dry spells.
The perennials L. siphilitica and L. cardinalis AGM need a moist habitat because they wilt in dry conditions, so are ideally placed next to a pond or stream. The L. hybrids are gross feeders and on poor soil they benefit from fortnightly applications of a balanced fertiliser in spring and early summer. They are typical herbaceous perennials, whose stems should be cut to ground level after flowering.
Lobelia plants are very attractive to slugs and snails and are also susceptible to crown rots. Perennials can be divided in spring or their fresh seed sown in autumn, but species hybridise readily and may not come true.
What the specialists say
Eva Aldridge, partner, Asterby & Chalkcroft Nurseries, Bedfordshire "Hardy Lobelia provide fantastic late summer colour. There isn't much that is showy at that time of year. The only bad thing is that slugs are very partial to them.
"I like L. x speciosa 'Tania' and L. x speciosa 'Monet Moment'. Both are very nice vigorous plants, with large flowers in a good strong colour. L. x speciosa 'Monet Moment' is unusual because it has pale rather than dark pink flowers.
"When it comes to the bedding types, I prefer the cutting-raised Lobelia because they produce larger plants and are more vigorous. The seed-raised types tend to go to straw if they dry out in a basket - I suppose the answer is to keep an eye on your hanging baskets.
"I think this year there may be a run on red and white varieties of Lobelia because people will be wanting to plant patriotic displays to support England this summer in the World Cup."
Diana Brown, partner, Cotswold Garden Flowers, Worcestershire "Lobelia are popular for their colour, the shape of the plant and because they flower from summer to early autumn. There's little negative to say about them. The winter hardiness of each species needs to be considered.
"The nicest one is L. tupa. It's quite hard to find but it has a stunning colour, though it's a bit tender and will die in a harsh winter. It should be propagated by seed. L. x speciosa 'Tania' is also very nice, with dark leaves and crimson-purple flowers. It can be propagated by division. And you mustn't forget L. cardinalis AGM, a good seller for us. It likes damp summers and dry winters, which makes it a bit difficult."
Robert Gamble, owner, Greentiles Nursery, Middlesex "We grow two main series of seed-raised bedding Lobelia - the Regatta series, which produce a trailing plant in colours including white, rose and mixed, and the Riviera bush type in midnight blue, sky blue and white.
"These produce plants similar in habit to Crystal Palace, but they are earlier to bloom. They are some of the more expensive varieties but it's worth it. Lobelia is pretty straightforward to grow. You just need to keep them at around 16 degsC to protect them from frost."
Jackie Nash, second buyer, Buckingham Nurseries "On the whole they look after themselves, just needing a bit of deadheading during the growing season and to be cut back when the new rosettes emerge. They like being kept moist but not sitting in water.
"Our garden centre is on an exposed site, so with L. 'Queen Victoria' we place it in a sheltered position to prevent it getting damaged during the winter. I have a soft spot for this variety - it may have been around for a while, but its foliage really compliments the flowers.
"To promote the new variety L. x speciosa 'Sparkling Ruby' and L. x speciosa 'Hadspen Purple' we put them on the display end of our A-Z benches outside. Lobelia give a good colour late in the year."
Species and cultivars
L. bridgesii is a rarely-seen, highly hardy species from the mountains of Chile, bearing spikes with lots of big pale pink, distinctive flowers, growing to 2m.
L. cardinalis AGM has cardinal-red flowers, between August to October. Rarely survives UK winters because it needs damp summers and dry winters.
L. cardinalis f. alba has spikes of delicately cut white flowers, with just a hint of pink on young flowers, between July and September. Height: 1m.
L. cardinalis 'Queen Victoria' AGM (often referred to as L. splendens/fulgens 'Queen Victoria) has scarlet flowers against distinctive red leaves, from July to October. Height: 75cm.
L. erinus is one of the main species used to produce bedding plants. A herbaceous perennial in the wild, in our climate it is treated as a half-hardy annual. Numerous cultivars have been selected for garden use, ranging from the dark blue 'Crystal Palace' to the red-flowered 'Rosamund' and the double-flowered 'Kathleen Mallard'.
L. erinus var. pendula is the trailing Lobelia from which the popular bedding series Fountain and Regatta are derived.
L. excelsa has large, felty leaves, like L. tupa, and long spikes of pale pink flowers with blue stamens, from June to October. Height: 75cm.
L. laxiflora var. angustifolia has elegant narrow foliage and long tubular orange flowers, with a prominent yellow lower lip, from July to October. Height: 60-80cm.
L. siphilitica has light green leaves and clear blue flowers from July to October. Height: 85cm.
L. siphilitica 'Alba' bears long heads of white flowers from July to October. Height: 85cm.
L. x speciosa 'Dark Crusader' has deep dusky green leaves and big floppy petals of darkest crimson-scarlet between July and September. Height: 85cm.
L. x speciosa 'Fan Tiefrot' (Fan Series) AGM has tall heads of soft pink-red flowers on dark stems between August and September, above dark foliage. Height: 70cm.
L. x speciosa 'Hadspen Purple' (PBR) has vivid purple flowers between July and September, held on upright flowering stems. The leaves are lance-shaped and green, with a purple flush. Height: 70cm.
L. x speciosa 'Kompliment Scharlach' AGM has tall purple stems with scarlet flowers from July to September. Also features dark purplish basal leaves with some on the flower stem. Height: 90cm.
L. x speciosa 'Pink Elephant' AGM is a tall variety with pink flowers between July and October. Height: 1.5-2.5m.
L. x speciosa 'Ruby Slippers' has large velvety ruby flowers from August to October. Height: 1m.
L. x speciosa 'Russian Princess' has deep magenta-purple flowers from July to October, set against dark foliage. Height: 85cm.
L. x speciosa 'Tania' has dark lustrous leaves and crimson-purple flowers between July and October. Its young shoots are pink. Height: 1m.
L. x speciosa 'Vedrariensis' is a tall variety with dark green leaves that become tinted red and bright purple flowers from August to October. Height: 90cm.
L. tenulor 'Blue Wings' has erect, slender stems, bearing large, gentian blue flowers, 2.5cm across. Excellent for summer bedding in a sheltered sunny spot.
L. tupa has broad, downy tobacco-like leaves and tall spikes of red flowers between July and December. Height: 1-3m.