Bloom machines: No fuss flowers to plant now
Calibrachoa and its close relative petunia love the heat, says DERYN THORPE, and are just as comfortable in a pot, basket or vertical garden as they are in the ground
For reliable colour throughout spring and summer, it’s hard to go past petunia and calibrachoa. Gardeners usually buy them as annuals, but they are actually short-lived perennials. They bloom year-round in warm climates, and in cool areas keep on flowering until serious frost arrives.
These undemanding plants flourish and flower most abundantly in sunshine but put up with semi-shade when planted in free-draining soil. They don’t like wet foliage or wet feet so let them dry out a bit between waterings to avoid problems.
There are 25 calibrachoa species and 35 annual and perennial petunias, all bar one originating in tropical South America. The exception is a calibrachoa that comes from southern parts of the US. All are in the nightshade (Solanaceae) family and are closely related to tobacco.
Originally called petunia, calibrachoa were renamed when a Dutch geneticist discovered chromosomal differences. He selected the name calibrachoa, which is pronounced cali–bra–co–a. I don’t know about you, but I find it a bit of a mouthful. The name honours a Mexican professor of pharmacy. Many people get around the tricky name by referring to them as million bells, which was the release name chosen by the Japanese biotechnology firm that introduced new strains of plants to the masses in the 1990s.
The best way to describe calibrachoa is that it looks like a petunia with miniature flowers. These are sprawling or prostrate plants with leaves less than 25mm long. Their small flowers have a short tube at the base and come in an astonishing range of colours (except true blue), which includes bicolours, veined flowers and double-flowering forms.
What’s really important is their vigour and ability to flower – indeed, few plants can out-flower a calibrachoa hybrid and, unlike petunia, they do not need to be deadheaded. Flowers are borne almost continuously when there’s adequate light and warmth and, while some have a more mounding form than others, all varieties trail gracefully.
Plants are usually produced by tissue culture and sold in pots or hanging baskets, but seed is available online if you want to try to grow them from scratch.
By contrast, all gardeners know petunias and easily recognise these low, spreading plants with downy, slightly sticky, rounded leaves and big funnel-shaped flowers with five fused lobes. The petunias we buy for annual colour are hybrids, bred mostly from P. axillaris and P. integrifolia, which were first hybridised in the 1830s.
Flowers come in all colours except true blue and orange, and can be single or double. Some have bicoloured flowers, contrasting veins and frilled edges. Many are sold in punnets of mixed colours that suit mass planting but plants can also be purchased in single colours to create your own colour scheme. See box (opposite) for interesting new petunia colours.
Some hybrids, especially premium spreading forms, are more expensive as they are grown vegetatively (from cuttings) while those raised from seed are cheaper. Packets of seed are also sold in nurseries.
Petunias flower best when deadheaded frequently, removing the portion directly below the flower where seed develops.
The flowers are damaged by overhead watering (including heavy rain), however today’s varieties are more water resistant and usually spring back after a drenching.
Both calibrachoas and petunias need a moist, well-drained, humus-rich soil. For best growth, incorporate compost in the soil prior to planting out seedlings. Spread organic mulch around them to conserve moisture. Both flower most profusely in full sun, though they take some shade in hot areas, especially in the afternoon.
To create a well-branched plant and encourage spreading growth, particularly with petunias, tip-prune the plant as it grows. As plants age, they can get leggy (develop long stems) but this is easy to fix. Simply cut them back (you can remove up to half the plant) and then watch them shoot back and become much bushier, with a fresh crop of flowers.
Petunias are traditionally used for colour at the front of garden beds, and since Victorian times have been popular
for providing massed colour. Varieties come in a number of widths, so check the planting information on the plant tag to work out how closely to space them.
Don’t just think about planting them in garden beds, as petunia and calibrachoa are perfect for pots, window boxes and hanging baskets, or spilling down from garden walls, where their trailing habit can be displayed to full advantage. Use them in strategically placed pots near your front door or living areas to create a continuous splash of colour. Remember to water them daily in summer.
I like to use both in mixed baskets as the ‘spiller’ element, adding upright plants such as regal pelargonium, grassy Carex ‘Feather Falls’ and perennial nemesia, which all like similar growing conditions.
While both plants like to dry out between waterings, when grown in fibre-lined hanging baskets the biggest challenge is to keep them moist. To conserve moisture, line them with plastic with three drainage holes before filling with premium potting mix.
The only pests that attack these plants are slugs and snails. They are also quite disease resistant but may get powdery mildew at the end of their lifespan, which means that it is time to pull them out and place them in the bin, not the compost.
Calibrachoa and petunias are heavy feeders. I prefer using a slow-release fertiliser for flowering plants and choose one that is active for nine months. Plants will flower more abundantly with fortnightly feeds of a liquid fertiliser containing fish and seaweed.