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

Gardening Australia - - CONTENTS -

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.

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