How to Grow Callas
Calla blooms are romantic blooms. Maybe it’s the soft, elegant lines of the tender half cones, or maybe it’s just because a bunch of these expensive flowers means somebody really cares about you; but there is no doubt that callas lend an air of exotic romance to the florist’s vase.
Gardeners are just as capable of adding that allure to their gardens if they pay attention to the native environment of Callas, which hail from the warmer, wetter regions of South Africa.
Protect them from frost, give them a constantly moist spot, and then dig and overwinter them if you’re in a growing zone north of Zone 8, and you too will be able to make your own romance in the garden in a range of colors from passionate red to purest white.
When & Where to Plant Callas
Plant rhizomes of callas in the late spring, when danger of frost is plant, covering with 1-2 inches of rich, humusy potting soil.
Select a part-shade spot in an area that benefits from constantly moist soil such as the edge of a pond, or in a container water feature. If planting in pots, use an organically-rich potting soil that drains well but retains moisture.
In zones where it can overwinter, such as in the Pacific Northwest, the white species type (Zantedeschia aethiopica) will not only spread but can be considered a bit of a pest. Unless dug in colder zones, it will perish when the temperatures plunge and must be brought inside. Growth is significantly lessened in this case.
Light: A partly-shaded spot is ideal, as too much direct sun on leaves and flowers can burn them. However, the plant needs light to bloom well, so deep shade is not a good option.
Soil: Callas need organically-rich, heavily fertile soil that is on the moist side to thrive. Average moist soils will also be tolerated, but dry soils will not.
Spacing: Space rhizomes 4-6” apart when planting a clump together, and space 12-18” away from other plants. If planting in pots, plant 2-3 rhizomes per 10-inch pot, or one per 6 inch pot.
Planting: Plant in spring when all chance of frost is over and nights have warmed. If you have a greenhouse or warm, well-lit area in your home, you can start the rhizomes earlier to put out plants in full growth when nights are warm.
How to Grow Callas Throughout the Season
Growth Habit: Species Calla such as Z. aethiopica can grow as tall as 2-3 feet, with shiny, undulating leaves that resemble large arrows. The flower is an arum type bloom that consists of a spathe – usually in white - and a yellow spadix. Colorful cultivars in shades from yellow to almost black to deep red are usually shorter (from 12-18”) and less hardy, with variations in foliage stippling. In warm climates, Callas will spread into large clumps, in colder climates they must be treated like an annual or dug and overwintered indoors.
Staking: No staking is necessary.
Watering: Watering is crucial when it comes to Callas. Keep them moist from the time they are planted until after they bloom and start to die back, when you can gradually withhold water. In dormancy during the late fall/winter months they should be kept just damp to prevent desiccation.
Fertilizing: Fat, rich soil is preferred when it comes to Callas. Plant in a compost-rich soil and feed with a balanced slow release organic fertilizer during the growing season.
Mulching: Mulch can help retain moisture in the soil, and is therefore recommended. Keep mulch away from the crown of the plant to discourage rot.
Callas: End of Season Care
Generally, the white species Calla are hardy to Zone 8, and foliage will remain green after flowering, to die back as days get colder or soils get drier. Many of the colorful hybrids are not as hardy and enter a period of dormancy after flowering.
Trimming & Pruning: Calla will not re-bloom if deadheaded (spent blooms trimmed off), but old blossoms will disfigure foliage as they die back, so removing them is recommended. Many of the colorful Calla cultivars will go dormant not long after flowering.
Dividing & Transplanting: If dividing larger clumps of Calla in warmer climates, dig the clumps and gently pull them apart. Use a sharp knife to divide them and replant. If dividing smaller, overwintered pots, look for offsets in the winter or early spring, cut them apart and let the cuts callus to prevent rot. Pot them up in rich soil in the spring so they can be monitored and set out in the garden when they get bigger.
Pests & Disease: Thrips can be an issue with Callas, as can several types of bacteria rot which will affect the rhizome and the crown of the plant. Infected plants must be discarded. Fresh, clean potting soil is recommended to prevent problems with disease, as is using clean, sharp knives to divide rhizomes and letting them callus over before replanting.
Additional Concerns: In warm climates (Zones 9-11) species Calla (white) will vigorously spread via seeds and rhizomes. All parts of Calla lilies are poisonous, and the sap can cause contact dermatitis in some people.
Callas: Extra Info
Design Advice: Callas make a wonderful accent for a pond garden, thriving in the marginal space between dry land and water, but can also be used within the pond itself, adding an exotic feel to water gardens.
Sink smaller pots of red callas into larger pots which contain the canna lily ‘Pretoria’ – setting off the deep red blooms of the Calla with the variegated yellow-green foliage of the canna. As the callas go dormant (after blooming), you can pull them, store them, and replace with shade-blooming annuals like begonias.
In warmer climates, use the taller species of Calla in unexpected places such as tucked into the corner of a wall or near a downspout where moisture is trapped and/or abundant. The background of the house or wall will set off the lovely, unusual foliage, and give them a boundary against which to grow.
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