Friday 26 August 2016

How to grow Zantedeschia

Mainly about hardy Zantedeschia aethiopica

red calla

Little did I imagine twenty years ago when Steven married Haley and the bride carried Arum lilies which also bedecked the tables that I would ever successfully grow these magnificent cut flowers. At that time I lived in dry Bolton Percy and without using copious watering they would never have thrived. With regard to watering I used to be rather self restricting and if an established  plant needed watering in the garden I felt it to be not worth growing. That included vegetables down on my allotment.
Now in my Seaton Ross garden zantedeshias are littered everywhere and make magnificent strong deep rooted plants that add brilliant white to the garden from May until September. My very deep sandy soil overlies clay that creates a water retentive basin. A huge ancient agricultural drain takes surplus water away and half of my garden boasts that rare condition of all year round well-drained moist soil.I have more than a dozen randomly distributed two to five foot high zantedeschia specimens. 
(Whoops I have written too soon and this August we have run into quite severe drought! My plants look healthy, some are setting seed but there will be no flowers for next month’s Open Day)

My Open Day guests will not be admiring my Zantedeschia ‘Crowborough’
Zantedeschia aethiopica ‘Crowborough’ is an almost fully hardy bog plant that can also be grown in a pond as an aquatic. I have doubts about its long term success in open water but it will certainly survive through the Summer! I would be very interested to hear of anyone who grows it permanently in the water. I tend to think that bog plants such as this arum and my own ten foot high gunnera prefer to be planted next to water but just a little above it where their roots can penetrate down.

My gunnera gets plenty of moisture but never stands in water - other than occasional Winter flooding
French interlude
My pictures of Brenda’s son’s zantedeschia in France provide some evidence of their permanent success in very shallow running water. They are absolutely six foot magnificent. The ancient traditional public laverie spills spring water into a very shallow stream that runs across his land. Needless to tell you I brought a few very small divisions home. With patience very small pieces after a few years made wonderful huge plants.

The water drains from this still used laverie
When Peter moved in I took several divisions from this plant that had established itself naturally and dibbed them into his stream

They soon established and now hold their own against Peter’s brambles and nettles (this was a good day)

In the water they make luxuriant shiny foliage 
and look very fine

Culture of  Zantedeschia aethiopica

The French variety has found my own garden to its liking
The methods of growing the hardy Crowborough variety and similar cultivars is very different to those for the widely available more compact coloured tender hybrids which I will consider below.
'Crowborough' is really quite hardy, especially when established. Mine survived the notorious 2010 ‘double Winter’ with minus eighteen centigrade air temperature registered in both January - March and December. Just!
Very small plants like the one I brought back from France get going better if you give them greenhouse protection for their first Winter.
They thrive in moist soil although many gardeners successfully grow them in ordinary deep  well drained soil. They are best undisturbed and go from strength to strength with each succeeding year. My own grow in a wide range of conditions but the plants in full light do the best.
Although the books correctly tell you that you can lift and divide them this does give the numerous propagules a considerable check. I prefer to notch or tease out pieces with a spade leaving the parent little disturbed. Small pieces can be potted for coddling in a greenhouse and larger divisions can be directly planted. My plants rarely if ever go completely dormant but are best divided in Winter or Spring. For the record my French rooted shoot was taken in August.
Your established plants need plenty of space when they will make strong large specimen clumps.
Do they respond to fertiliser? Are they better with mulching or adding extra organic matter? Probably yes but I never bother. Do they get pest and disease? I have never noticed - except the tiny black insects that show up on the flowers.
Should I let them seed? Probably not and I remove the dead flowers to encourage more. Do they need staking? No.
Growing the coloured hybrids

For fifty years I had ignored the coloured hybrids that are sold as ‘bulbs’ every Autumn and Spring. Early failures with rotting-off tubers and weak spindly growth when directly planted in the garden persuaded me that they were a complete waste of time. Especially so when I knew them not to be Winter hardy and be best started off early with artificial heat. 
Although I do love our heated conservatory, artificial heat for greenhouses has never been the way for me. Many texts wrongly quote rather high minimum starting temperatures as essential for these so called callas. That might be appropriate for commercial cut flower growers but not for me.

Brenda’s son Steven lives in balmy Folkestone and his coloured zantedeschia is permanantly established in the ground

Last year I decided to try some coloured calla cultivars in my unheated greenhouse. ‘Unheated’ is a bit of a misnomer as so called cold greenhouses heat up very well with the sunshine. Even better the warmth is suffused with healthy light. Artificial heat in a greenhouse on dull days very early in the season is not usually a good  gardening option!

I am still on my learning curve. In researching this post I learned that these coloured zantedeschias like it rather drier than the hardy species. Especially when starting in their pots and before new growth appears when the roots can easily rot. Like any plant that grows luxuriantly when they get going they then need plenty of water.
I  grow them in large pots of my own sandy soil enriched with slow release fertiliser and regularly top dressed with my yaramila general fertiliser. Most gardeners chose to liquid feed. My plants are stood outside throughout the Summer.

An advantage of tubs is that they can be temporarily placed next to a wide range of plants
I have fallen in love with these coloured hybrids.
Less strong first year plants bulk up each succeeding year. In my second year I have not chosen to divide them.
I overwintered the dormant tubers last Winter, still in their pots almost unwatered in my unheated greenhouse.
I think I was lucky as it was a very mild Winter! I have written before how I lost tender plants in containers in the 2010 Winter when for example agapanthus survived outside in the ground when those in the unheated greenhouse died. I am confident that my tender zantedeschias would survive in the greenhouse in a normal winter but in fear of a harsh one I will this year overwinter the tubs in my almost frost free garage.

My niece Gail recently admired my coloured callas and reminded me that they were her wedding decoration too.

red calla
They seem to be rather popular at weddings

I wrote about growing agapanthus last year


  1. I have a couple of Zantedeschias growing in pots that overwintered outside last year. Both are quite small. One is standing in a saucer of water and the other is in our puddle pond. A tiny pond the size of a puddle. Neither flower. I had thought of planting one in a basket in our larger pond. It is filtered. so there is some movement of water.
    My sister has a dark purple cala - well several actually that seem to have seeded themselves into troughs in her garden. These have just been left to their own devices. They disappear over winter and then pop up again late spring/early summer. They were bought as houseplants and then consigned to outdoors when they refused to flower. Just one of them has one flower this year.

    1. Fascinating Sue and in the wilds of Wakefield!
      It would be a very interesting post on your blog and we might be introduced to your green fingered sister
      It is also an illustration how sometimes plants establish themselves despite all efforts with stuff bought at a shop

  2. How very interesting Roger. This is a plant I have wanted to grow for a long time.Here no doubt I would have to overwinter them in pots. I have often see them in Victoria B.C. There they are usually in the ground and are not cosseted in any way. In pictures of exotic gardens they seems to often grow in water (ex. Ninfa in Italy).
    They only time I tried, I buried the plant for the winter. When I dug it up in spring instead of one pant there were dozens of tiny bulbs none of which did much of anything.
    Your information will be very useful when I try again. The problem is finding it for sale as they never are carried around here since they are not hardy. Thank you again for all the information.

    1. Thanks Alan.Those bulbs were perhaps too small to get going?
      I must be more alert to looking for zantedeschia growing in water and try and get some pictures to add to the post

  3. My 2 Crowboroughs, one in front white garden and other in back garden, even though where we are is wet wet wet, they are no-where near as large as yours, or any of the photos.

    1. I know how wet you are in Preston Bagpuss!
      I think the size is a factor of my clumps having space to themselves in an open situation and time!
      They will look great in your white border!
      ps my french variety is bigger than Crowborough

  4. I grow both Zantedeschia aethiopica and various types of hybrid zantedeschias – I don’t think my aethiopica is a named variety, at least there wasn’t anything on the label to indicate so, but I have had it since 2011 and it is absolutely enormous. I actually wrote about it on my blog post yesterday, but I didn’t post a very good photo to show the size of the whole plant. Mine is still flowering and has flowered since early June, started 4 weeks later than normal due to the cold spring. Mine doesn’t die down during the winter, just loose some leaves and look a bit sad for a while before it springs into action again. It has lived in a container all the time and doesn’t get moved inside, wrapped or get any special treatment. I feed it with Q4 a few times per year when I remember, but I think the key to a happy, flowering Zantedeschia aethiopica is water, water and more water. I give mine a bath every evening – I fill up the container with water up to the rim and I do this every time I water the garden. Has worked well for all the years I have had it.
    My coloured callas were all started this winter so some flowered this summer, some didn’t. I hope they will be more successful next year as those 3 that flowered this year were absolutely stunning. I kept mine in the shed until I was sure there would be no frost and the temp was above 5 degrees at night. These callas do not get a bath :-)

    1. Thank you for your cultural information HELENE. I visited your post to see your healthy plant and all your other beautiful pictures.
      I did not reveal on my own post that i have five coloured callas in pots but like you only three flowered! Two really healthy plants have produced nothing!

  5. Such beautiful photos!
    I should try to grow coloured callas, especially the pink ones. The white ones are (still) considered funeral flowers here. :)
    In our cold climate, they should be grown in containers and overwintered indoors.
    Thank you for the appealing post! The comments are very interesting as well.

    1. At my age we go to more funerals than weddings Sara!
      Yes a lot of people associate zantedeschias with funerals but I love to see them at weddings.
      I don't like the idea of being restricted by fashion!

    2. PS Informed comments are very much part of a blog.I am proud of some of my regulars and they keep me on my toes.

  6. I planted some Zantedeschia aethiopica in April this year and although I have plenty of green foliage they have not flowered. My soil is not well draining and I live in the south US so it's very humid in the summer, where they are planted they get full sun. Any idea why they have not flowered would be appreciated.

    1. They do not always flower in the first year if they were small plants. Your conditions sound ideal. Better things next year Minnie


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