Overwintering calla lilies: how this exotic species survives the cold season

Even an exotic plant like the calla lily can survive our winter unscathed. We show when, where and how to successfully overwinter calla lilies and how to properly care for them in the cold months.

The calla lily (Zantedeschia aethiopica) is often also called zantedeschia. It is known as an exotic plant that appeals for its large, imposing flowers. It can be kept both as a houseplant in a pot to add a jungle vibe to the home or office or to decorate the garden in summer. Unfortunately, however, these plants can not spend the winter outdoors. In this article, we explain how to keep your calla lily for many years.

Are calla lilies hardy?

The calla lily does not originate from Ethiopia, as its botanical name Zantedeschia aethiopica would suggest, but from South Africa. There, the plant is spoilt with year-around warm temperatures, which actually never fall below 20 °C. Accordingly, calla lilies are not hardy and cannot overwinter outdoors in our country. But exceptions prove the rule, as we all know. For example, there is actually a calla lily variety that has been specially bred for frost tolerance. ‘Crowsborough’ blooms in summer and is said to withstand temperatures as low as -20 °C. Specifically, this means that in winter the above-ground parts of the plant of this hardy variety of zantedeschia freeze off or are cut back. The tubers remain in the ground all winter and can resprout in the spring. As calla lilies continue to grow in popularity in the garden, it is surely only a matter of time before new frost-tolerant calla varieties are bred.

Summary: are calla lilies hardy?

• Normal varieties are not hardy
• The only exception is the ‘Crowsborough’ variety
• Its tubers can withstand sub-zero temperatures down to -20 °C

Tip: Pay attention to your calla lily to make sure it is a genuine Zantedeschia aethiopica. It is easily confused with the marsh calla (Calla palustris), also called dragonwort, which, in contrast to the zantedeschia, is native to the northern hemisphere and very hardy.

Overwintering calla lilies: our care tips

In its native South Africa, the zantedeschia does not get four, but only two seasons: the dry and the rainy season. Therefore the calla lily also requires strict growth seasons for magnificent growth in this country. This means that during the growing season in summer it needs the highest possible temperatures and enough water, while in winter cool temperatures and drought are needed. Let us show you how to create ideal winter conditions for calla grown both indoors and outdoors.

When does it get too cold for the calla lily?

Callas or zantedeschias are unfortunately susceptible to frostbite and are quickly damaged if temperatures are too low. Indoor callas in pots get too cold at temperatures below 15 °C and should be brought into the warm quickly. Zantedeschias that are planted out in summer or spend them in pots in the garden need appropriate measures from temperatures below 10 °C in order to survive the winter safely. As already mentioned, the only exception so far is the hardy ‘Crowsborough’ calla lily variety, which can withstand temperatures as low as -20 °C.

Overview: When is it too cold for the zantedeschia?

• Indoor calla: From temperatures below 15 °C
• Outdoor calla: From temperatures below 10 °C
• ‘Crowsborough’: survives frost as a tuber up to -20 °C

Overwintering calla lilies: how and where?

Overwintering indoor and garden calla lilies is seriously different. While indoor callas can be overwintered as a whole plant, garden callas are dug up in autumn and only the tubers are stored for the winter. First, let us take a look at how best to overwinter your indoor calla lilies: Even in winter, the zantedeschia needs a location that is as bright as possible, for example on the windowsill. However, you should avoid direct sunlight at all costs. The temperature becomes critical, because it should remain constant throughout the winter and, if possible, not fluctuate. At a constant 10 ° C, a calla in a pot will survive the winter without damage.

Summary: Overwintering indoor calla lilies

• Bright location without direct sunlight
• Ideal temperature: 10 °C
• No temperature fluctuations

Garden callas require a few more steps to get through the winter. Start preparing as early as August by completely stopping fertilisation and gradually decreasing watering. Then, in early October, it is time to dig up the plant’s storage organs, the tubers. Only these will be overwintered. From the excavated callas, cut back all above-ground plant parts to five centimetrea. Carefully tap or brush off the soil from the tubers. Now dry the tubers on a rack for two to three days. Then the zantedeschias are ready to move into their winter quarters. For this purpose, choose a dark, dry place, for example, a cellar. When overwintering callas, temperatures should never rise above 15 °C, otherwise the plants will begin to sprout. However, the temperature should not fall below 0 ° C, otherwise the tubers will freeze. Place the tubers in a box filled with dry sand or dry straw. This allows the calla lily tubers to rest over the winter and be planted out again in the spring.

Overwintering outdoor calla lilies: summary

• From the end of August, water less, stop fertilising
• In early October, dig the tubers from the ground
• Cut back all above ground plant parts to 5 cm
• Remove soil
• Allow tubers to dry for 2 – 3 days
• Overwinter in a box with dry sand or straw
• Store in a frost-free, dark and dry place
• The temperature should always be below 15 °C.

Caring for calla lilies in winter

As already mentioned, winter is the dry season for calla lilies. That is why they should be watered very sparingly. Allow the substrate to dry out almost completely before watering – in very small quantities. Also avoid fertilising during the winter months. Unfortunately, zantedeschias are often attacked by pests in the cold season. Therefore, regularly check the plant for pest infestation. Typical pests of indoor calla lilies are leaf aphids (Sternorrhyncha) and spider mites (Tetranychidae). Wilted leaf margins and discoloured leaves, on the other hand, indicate root rot, caused by watering too frequently. If you regularly remove dead plant parts from your houseplant, your calla lilies will not need pruning. In spring, you can slowly prepare the calla for the rainy season by first increasing the temperature to 12 or 15 °C. Now the plant will slowly begin to grow again and therefore needs more water. But do not overdo it in the beginning, still water moderately. Garden calla lilies, which are overwintered as tubers, do not require care over the winter.

Calla lilies care in winter – Overview:

• Only water indoor calla lilies very sparingly
• No fertilisation
• Regularly check for pest infestation
• Regularly remove dead plant parts
• In spring, slowly increase the temperature to 12 – 15 °C
• Gradually increase watering – growth adjusted
• Callas that are overwintered as tubers, do not require care

Tip: always wear gloves, because all plant parts of calla lilies are poisonous.

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If you have overwintered your calla lilies as tubers, you have two options for putting out the plant in the spring. Either plant the tubers in a pot first and let them grow indoors, or ignore this step and plant them directly outdoors when frost is no longer expected. If the tubers are planted in pots first, you’ll give the plants an advantage and they’ll begin to bloom earlier in the year. To do this, prepare a pot of potting mix, which you should enrich with a fertiliser with slow-release effects. Our Plantura Flower Food is particularly suitable for this, as it contains all the important nutrients your calla lily needs. Now the tuber should be placed in the pot ten centimetres deep, covered with substrate and watered. The calla can then grow well in a bright place at room temperature. Water it regularly, increasing the amount of water in proportion to their growth. Finally, in mid-May, the plant can be transplanted outdoors.

Alternatively, you can plant the overwintered tubers directly into open ground at the end of May – either in garden beds or in pots.

How should you overwinter outdoor calla lilies?

• Remove tubers from winter storage in early March
• Fill a pot with substrate and a long-acting organic fertiliser
• Plant tuber 10 cm deep
• Water well
• Put in a bright place at room temperature
• Steadily increase watering quantity in proportion to growth
• Plant out in the middle of May
• Alternatively, do not plant indoors in spring, but plant tubers directly into garden beds or outdoor pots in mid/late May.

Not all plants need to be overwintered with as much effort as the calla lily. Many perennials are hardy and can easily survive the cold season in the garden.