From a botanical perspective, the most critical point to understand is that "white" calla lilies (Zantedeschia aethiopica) and "colored" calla lilies (typically cultivars of Zantedeschia elliottiana, Zantedeschia rehmannii, and hybrids) belong to the same genus, Zantedeschia. This means their fundamental biology and growth cycles are very similar. Both grow from rhizomes, produce their iconic flower structure (which is actually a specialized leaf called a spathe surrounding a central spike of tiny flowers, the spadix), and require a period of dormancy. The primary differences in care arise from the specific environmental adaptations of their ancestral species, which have been carried over into our garden varieties.
The most significant difference lies in their root systems and subsequent water requirements. Zantedeschia aethiopica, the white calla, is naturally found in marshy areas of South Africa. Its rhizomes are adapted to consistently moist, even waterlogged, conditions. As a result, white callas are remarkably tolerant of water and can even be grown as marginal aquatic plants. They prefer their soil to be kept evenly moist throughout their growing and blooming season. In contrast, the colored hybrids originate from species that inhabit more well-drained, seasonally dry slopes. Their rhizomes are more susceptible to rot if left sitting in soggy soil. Therefore, the care for colored callas involves a "soak and dry" approach: water thoroughly when the top inch of soil feels dry, but allow excess water to drain away completely.
While both types require a dormant period, the environmental cues that trigger dormancy differ. The white calla lily often enters dormancy in response to a combination of drought and high temperatures in late summer. In milder climates, it can be semi-evergreen if moisture is provided. Colored calla lilies, however, are more strictly deciduous. Their dormancy is triggered by the natural end of their growth cycle and a reduction in daylight after flowering. As the foliage yellows and dies back in late summer or early autumn, watering should be reduced significantly for both types to allow the rhizomes to rest. However, the colored varieties are more dependent on this dry rest period to initiate flowering the following year.
Both types thrive in full sun to partial shade, but their ideal conditions show subtle variations. White calla lilies can tolerate, and even prefer, partial shade, especially in hotter climates where intense afternoon sun can scorch their leaves. Their moisture-retentive nature helps them cope with heat. Colored calla lilies, on the other hand, generally require more sunlight to produce their vibrant spathe colors. They perform best with at least 6 hours of direct sun per day. In terms of hardiness, Zantedeschia aethiopica is more cold-tolerant, often surviving winters in USDA zones 8-10 if mulched heavily. The colored hybrids are more tender, typically hardy only in zones 9-10, and their rhizomes must be lifted and stored indoors over winter in colder regions.
The nutritional needs of both types are similar but should be aligned with their growth cycles. All calla lilies are heavy feeders during their active growth period. A balanced, water-soluble fertilizer applied every two to four weeks will support lush foliage and strong flower production. The key difference in care relates to the dormancy period. Fertilization must be completely halted as the plants begin to yellow and enter dormancy. Applying fertilizer during this time can harm the resting rhizome. The high-energy production of the vividly colored spathes in hybrid varieties may suggest a slight benefit from a fertilizer with a higher phosphorus content (the middle number in N-P-K ratios) to encourage blooming, but a balanced fertilizer is generally sufficient for both.
