A Gardening Journal

Giant Calla



This year, I added pots of callas to the tank that normally gets just pots of papyrus.  Finally—it's October, for heaven's sake!—the callas are in bloom.  Thank goodness I wasn't relying on plenty of flowers June through September, when this water garden—right by the terrace—is in full view of every single visitor.  OK, I was relying on them.  Silly me:  Big white callas are cool-weather bloomers.


Now I know that October is just the beginning of their flowering season—and in a week they'll all go back in the greenhouse where no one will see their peak flowering but me.  Sigh.


Another disappointment:  This cultivar is 'Hercules', which the nursery (Kartuz, in California) describes as being enormous, people-high, even.  But on the East Coast?  Not: Here's their additional comment at the plant's listing: "It seems that climate has a lot to do with the eventual size of calla lilies."  'Hercules' may be huge in the Bay Area, but he's just plain-old-calla size in Rhode Island.  Humph.


True, from any direction and at any size, calla flowers and leaves are exciting in New England. 




For a better chance next season of having callas in Rhode Island that really will get people-high even though they're not swanning about San Francisco, I'll try 'White Giant'.  Then we'll see if Hercules is the biggest guy on the block or not.



Here's how to grow this iconic water-loving perennial:

Latin Name

Zantedeschia aethiopica 'Hercules'

Common Name

Giant Calla


Araceae, the Arum family.

What kind of plant is it?

Rhizomatous herbaceous perennial.


Zones 7 (some sources say 6) - 11


Thickly growing in weed-proof colonies that, given encouragement, will expand to sizable swaths of groundcover.

Rate of Growth

Fast when happy.

Size in ten years

'Hercules' reaches maximum size (alas for me, in Rhode Island) only in cool-Summer climates with frost-free Winters:  San Francisco, say, where it can become five feet tall and spread indefinitely if growing in rich mud alongside still fresh water.  Back East, in containers sunk into a water garden for the Summer, it's still quite vigorous but the foliage isn't even two feet tall.  Abloom in the greenhouse in the Fall into Winter, the flowers are only a bit taller.


Thick and tropical. 

Grown for

its foliage.  The eagerly upward-pointing leaves have thick stems, and are a rich green that powerfully sets off the brilliant white flowers.  The plants grow so thickly overall that they make a great groundcover. 


its flowers.  Huge white "cowls" six inches across and tall, forming an inverted "Ming the Magnificent" cape around the yellow and, frankly, phallic spadix. These are the long-stemmed callas that long-stemmed movie stars, socialites, and heiresses in 1930's black-and-white comedies received as bouquets of dozens.  It's a flower of drama but also one that calls into question your pristine character; I'm sure callas drove Aubrey Beardsley as wild as they did those movie stars. 


its enthusiasm.  If you can provide enough water, a mild climate, and, usually, some shade in the afternoon, callas can prosper to the point of weediness.

Flowering season

Where hardy in-ground, flowering in cooler weather.  In low-land subtropics where it's scorching in Summer and cooler but mostly frost-free in Winter (Florida, say), flowering in late Winter and Spring and sometimes again in the Fall.  In high-elevation tropics (Quito, Ecuador, say), where temperatures are always cool but are also frost-free, flowering can be year-round.


This habit of cool-weather flowering also persists when callas are kept growing year-round in containers that are Summered outdoors:  You'll have plenty of foliage all Summer but few if any flowers.  You'll have plenty of foliage and flowers during the Winter provided the plants get enough light and water.


Rhizomes can be overwintered bare-root and dormant (and are usually purchased this way, too).  When potted up for warm-weather use they usually don't flower until—you guessed it—temperatures start to cool off in late Summer and Fall.


White callas, then, are not the plant to grow for specifically Summer display.  (Callas with colorful flowers, though—see "Variants" below—are much more likely to bloom in warm weather.)


In Zone 8 and up, callas are fully hardy and prefer afternoon shade unless they have absolutely unlimited water.  Farther north, callas do best with more and more sun—provided, though, that they, too, can enjoy all possible water.  Callas will grow in rich beds provided you water enough, but it's much easier to grow them in water gardens, in containers whose tops are at water level or submerged a couple of inches.

How to handle it

The iconic exotic glamour of calla flowers, plus the lush "easy"—and I mean in a moralistic way—growth of the foliage, taints the entire plant as a tropical interloper in temperate gardens in the same way as palms.  Both are exciting and effective in containers, where they are, clearly, not part of the year-round horticultural decor.  But both are a bit suspect growing in the ground outside of blatantly subtropical climates even when they're quite hardy. 


Growing callas in containers, then, is definitely the way to have your cake and eat it, too.  Callas need so much water, though, that it's not really practical to grow them in containers unless they're sitting in water or even submerged a couple of inches.  Fortunately, such shallow submergence is just what callas crave.  Then their thick vertical foliage arises (seemingly) directly out of clear water, pointing strongly upward until the dense growth of the fast-increasing colony forces the perimeter leaves into a lush outward lean. 


It's a beautiful and bosomy display in itself, and when the flowers appear (in cooler weather only), the show is guaranteed to be show-stopping—at least for those of us who don't live where callas are truly hardy.  Some places in Australia are so beset with naturalized colonies that they are battled like weeds.  In Northern California callas can also be "just part of the furniture," at home in ditches as well as moist woods.  In these climes, callas are as ho-hum as the agapanthus that crowd the parking-lot islands or the oleander that grows by the miles along the highways.


Callas can be kept in growth year-round as long as they're frost-free, but are hardy enough to be killed back to the ground for the Winter and survive until Spring even in the "real" Winters of Zone 7 and, maybe, even into Zone 6.  As usual, though, the constant water that enables the lush growth in frost-free months helps rot the dormant rhizomes in the quite-frosty-indeed months.  Below Zone 8, then, if you're not already growing your callas in containers it's better to dig them up in Fall.  You can pot them up for continued growth (and flowering) in Winter—in which case go ahead and cut most of the leaves off before you even dig the clumps up:  Their thick stems will snap the moment you try and handle the plants, and new leaves will grow quickly, anyway.


Or gently free the rhizomes from most of the soil and spread them out on newspaper to dry (i.e., "cure") for three weeks in a gentle environment: one that's frost-free with decent but not breezy ventilation, and that's light but not in direct sun.  Then store them in slightly-dampened peat moss in a cool (low 40's or even high 30's) basement.  Pot up in rich soil in late Winter so they can sprout indoors; submerge in the outside water garden after Spring is settled and benign. 


Standard "florist" callas, like 'Hercules' and 'White Giant', are cool-weather bloomers that don't provide more than lush foliage (lovely as it is) to Summer gardens.  Callas in containers that are overwintered in greenhouses can bloom beautifully when they receive the cool (down to fifty or even lower) night temperatures they crave, but they are also susceptible to mealy bugs and, when it's too hot and dry, spider mites.  Either overwinter your callas in a very cool greenhouse, then, or store them in the basement as bare-root rhizomes; see "How to Handle It" above.


The taller cultivars (including 'Hercules') don't seem to achieve maximum (or, often, even notable) height outside of cool-subtropical climates; enjoy them as giants only in Northern California and the Pacific Northwest, then, but not Southern California, nor back in the sweltering East.   


Callas offer the same too-tempting potential to hybridizers as coneflowers: Every year there's another cultivar with even more surprising and—at least to calla luddites like me—inappropriate coloring.  Already, spathes (the flaring Ming-the-Magnificant hood; the flowers themselves are on the phallic spadix) can be had in pink, green-white bicolor, lavender, purple, orange, butter-yellow, and ebony.  Leaves can be spotted or all-green.  Some cultivars are billed as notably taller or shorter.  To me, all the colorfully-flowered callas look more like houseplants.  Leave me just a few of the various 'White Giant' cultivars; you're welcome to the rest.


On-line and at nurseries.


Where not hardy, by division in Spring; where hardy, by division in Spring or Fall.  

Native habitat

Zantedeschia are all native to South Africa; 'Hercules' originated from Western Hills Nursery in Northern California.  

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