I recently received a flowering Zantedeschia hybrid lavender lily whose leaves are turning yellow. I would like to save the bulbs to plant outside. What steps should I follow?
Your message doesn’t indicate where you are gardening, and the answer depends on your climate. It also depends on which species of Zantedeschia you have. Based on the color you mention (lavender), I would guess you have a more tender hybrid.
Just in case you decide to keep your plant indoors, I am including information from The Complete Houseplant Survival Manual by Barbara Pleasant (Storey, 2005), which says that Zantedeschia hybrids grown indoors can be brought back into bloom (inside) in future seasons if you give them a rest period in late summer: “Allow the plants to dry until the leaves wither, clip off the old foliage, and keep the pots very lightly moist in a cool, shady spot. In winter, a fresh pot of soil, along with warmth, moisture, and bright light, will quickly bring them back to life.”
However, you say that you would like to grow your plant outdoors. If the variety you have is especially tender, it may not work, but you can certainly try.
According to Sunset Western Garden Book (2007), in its hardiness zone Zantedeschia can be planted fall through early spring, setting the rhizomes 4 inches deep, and 1 foot apart. If your garden is outside the plant’s cold hardiness zone, you would store the rhizomes when the leaves die back, and keep them over the winter in a cool, dry place, planting them out in spring.
Here is information from the Royal Horticultural Society.
Excerpt:
The tender forms of Zantedeschia are mainly cultivars of Z. elliotiana and Z. rehmannii (also called Elliottiana hybrids and Rehmannii hybrids), but may also include Z. albomaculata and Z. jucunda. These are often referred to as calla lilies.
These tender varieties can be displayed either as houseplants or seasonal outdoor bedding displays. They will flower in summer. If used outdoors, you will need to lift the rhizomes before the first frosts and store them over winter before replanting them next spring when the risk of frost is passed. Store them in trays of compost in a cool, dark, frost-free place such as a garage or shed. (…)
Tender forms: Require a minimum temperature of 10 degrees C (50 degrees F) so need overwintering indoors or in a warm greenhouse or conservatory. Plants that have flowered at Easter can be kept growing over the summer and repotted in spring. Alternatively, they can be allowed to dry out in late June and rested for a couple of months in a dry and dormant state before repotting in late August or early September for an earlier show of flowers.