Even an exotic plant like the calla can survive our winter unscathed. We show when, where, and how to successfully overwinter Callas and how to properly care for them in the cold season.
The calla ( Zantedeschia aethiopica ) is often also called Zantedeschia. What is meant is an exotic plant that convinces with its large, imposing flowers. As a houseplant in a pot, it can create a jungle feeling in the apartment or office, and it can also decorate the garden with its blossoms in summer. But with one exception, these plants cannot survive the winter outdoors. In this article, we explain how you can keep your Calla for many years.
Are Callas hardy?
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The calla does not come from Ethiopia, as the botanical name Zantedeschia aethiopica would suggest, but from South Africa. There the plant is spoiled with year-round warm temperatures that actually never fall below 20 ° C. Accordingly, Callas are not hardy and cannot overwinter with us outdoors. But, as is well known, exceptions confirm the rule. There is actually a Calla variety that was specially bred for frost tolerance. ‘Crowsborough’ blooms in summer and is said to withstand temperatures down to -20 ° C.
Specifically, this means that in winter the above-ground parts of this winter-hardy Zantedeschia variety freeze off or are cut back by you. The tubers remain in the ground all winter and can sprout again in spring. As Callas are becoming increasingly popular in the garden, it is certainly only a matter of time before new frost-tolerant calla varieties are bred.
Summary: are callas hardy?
- Normal calla varieties are not hardy
- The only exception is the ‘Crowsborough’ variety
- As a tuber, it can withstand freezing temperatures down to -20 ° C
Hibernating Calla properly: Our care tips
From its home in South Africa, the Zantedeschia has no four, but only two seasons: the dry and rainy seasons. Therefore the Calla needs strict growth phases for splendid growth with us. This means that during the growing season in summer it needs the highest possible temperatures and sufficient water, while in winter cool temperatures and drought are necessary. How to create the ideal conditions in winter for both the indoor calla and the calla in the garden, you will find out in the following sections.
When does the calla get too cold?
Callas or Zantedeschias are unfortunately chilblains and are quickly damaged if the temperature is too low. Room callas in the pot get too cold at temperatures below 15 ° C and they should be brought into the warm quickly. Zantedeschias, which are planted out in summer or spend in pots in the garden, require appropriate measures from temperatures below 10 ° C to get through the winter safely. As already mentioned, the only exception so far is the hardy calla variety ‘Crowsborough’, which can withstand temperatures down to -20 ° C.
Overview: When does it get too cold for the Zantedeschia?
- Room calla: From temperatures below 15 ° C
- Garden calla: From temperatures below 10 ° C
- ‘Crowsborough’: As a tuber, withstands frost down to -20 ° C
Wintering Calla: how and where?
The wintering of indoor callas and garden callas is very different. While indoor callas can overwinter as a whole plant, callas are dug out of the garden in autumn and only the tubers are stored for the winter. First, let’s take a look at the best way to overwinter your room calla: Even in winter, the Zantedeschia needs the brightest possible location, for example on the windowsill. However, you should definitely avoid direct sunlight. The temperature becomes critical because it should remain constant throughout the winter and, if possible, not fluctuate. At a constant 10 ° C, the calla in the pot survives the winter unscathed.
Summary: overwintering calla in a pot:
- The brightest possible location, but no direct sunlight
- Ideal temperature: 10 ° C
- No temperature fluctuations
With the garden calla, a few more steps are necessary to get the plant through the winter well. Start the preparation as early as August by completely stopping the fertilization and gradually reducing the watering. At the beginning of October, it is time to dig up the plant’s storage organs, the tubers. Only they are overwintered. Cut all the above-ground parts of the plant back to five centimeters from the excavated callas.
The soil is also carefully knocked off or brushed off the tubers. Now dry the tubers on a grid for two to three days. Then the Zantedeschias are ready to move into their winter quarters. A dark, dry place, such as a basement, is suitable for this. When the callas hibernate, the temperatures should never rise above 15 ° C, the plants will begin to sprout. The temperatures should not drop below 0 ° C, the tubers will freeze to death. Put the tubers in a box filled with dry sand or dry straw. In this way, the calla tubers can rest for the winter and be planted again in the spring.
Hibernate garden calla: Summary:
- Waterless from the end of August, stop fertilizing
- Dig up the tubers from the ground at the beginning of October
- Cut back all the above-ground parts of the plant to 5 cm
- Remove soil
- Let the tubers dry for 2-3 days
- Winter in a box with dry sand or straw
- Store in a frost-free, dark, and dry place
- Temperatures should never exceed 15 ° C
Maintain calla in winter
As already mentioned, winter is the dry season for Calla. That is why it is poured very sparingly. Let the substrate dry out almost completely before you water again – in very small quantities. There is no fertilization at all in winter. Unfortunately, pests often hit zantedeschias during the cold season. You should therefore regularly check the plant for pest infestation. Typical pests on the room calla are aphids ( Sternorrhyncha ) and spider mites ( Tetranychidae ). Wilted leaf margins and discolored leaves, however, indicate root rot, caused by too frequent watering.
If you regularly remove dead plant parts from your houseplant, your calla won’t need pruning. In spring you can slowly prepare the calla for the rainy season by first increasing the temperature to 12 to 15 ° C. Now the plant slowly begins to grow again and therefore needs more water again. But don’t overdo it in the beginning, still water moderately. Garden callas that are overwintered as tubers do not require any maintenance over the winter.
Caring for calla in winter – overview:
- Water room callas only very sparingly
- No fertilization
- Check regularly for pests
- Regularly remove dead plant parts
- In spring slowly increase the temperature to 12-15 ° C
- Constantly increase the amount of water, adapted to the growth
- Callas that are overwintered as tubers do not require any care
If you have hibernated your calla as a tuber, you have two options for wintering the plant out in spring. Either you plant the tubers in the pot first and let them grow in the apartment or you can save yourself this step and plant the tubers directly outside when frost is no longer expected. Planting the tubers in pots first will give the plants an edge and they will start to flower earlier in the year. For this, prepare a pot with potting soil, which you enrich with a fertilizer with an organic long-term effect.
Organic flower fertilizer, which provides all the important nutrients for your calla, is particularly suitable for this. Now the tuber is placed ten centimeters deep in the pot, covered with a substrate, and watered. The calla can then grow well in a light place at room temperature. Water them regularly, increasing the amount of water in proportion to growth. The plant can finally be transplanted outdoors in mid-May.
Alternatively, you can plant the overwintered tubers directly outside at the end of May – whether in the garden bed or the pot is up to you.
How should one hibernate garden callas?
- Get the tubers out of the winter quarters at the beginning of March
- Fill the pot with substrate and fertilizer with organic long-term effects
- Plant the tuber 10 cm deep
- Water well
- Put in a bright place at room temperature
- Increase the watering amount in proportion to the growth
- Plant out in mid-May
- Alternatively, no preparation in spring, but plant the tubers in the middle/end of May directly in the garden bed or the pot outdoors