Sunday, 27 September 2015

Growing hardy cacti outside in the UK

Home on the range

This opuntia was completely undamaged by 18 degrees centigrade of frost for three weeks in 2010

You might think growing cacti outside all the year round was nye on impossible in York! You might be right!
For several years now I have had a degree of success with growing cactus outside. Cactus were my childhood passion!
My first plant ever was a cereus barrel cactus. It was quickly followed by the succulent Sedum rubro-tinctum, a rather insignificant plant but one that fascinated me because the globular succulent leaves would root and then grow. It is easy to forget the thrill of rooting ones first cutting. I subsequently grew a dozen or so cactus for several years in my parents barely heated conservatory. When I went to horticultural college I put such childhood things behind me. Marilyn my sister took over my collection and it's remnants survive in her house to this day!

Now in my dotage I have been growing cacti outside for several years.Today, I am being rather self indulgent. Hardly anyone shares my interest and nobody read my previous post. What is the point of having a blog if I cannot write for myself?
All these have proved to be hardy and have been completely outside for several winters now

Just occasionally a visitor shows an interest. Cactus growers are very peculiar and dedicated people. I love them all, they are fascinating folk!
Allan in Orkney used to grow magnificent cactus at Askham Bryan College. He is my editor in chief and I regularly receive an e-mail missile with my latest spelling mistake which I immediately change. I had better watch what I say today!

About my indulgence
I originally researched on the net about hardy cacti and discovered there were several sources such as the Cactus Shop. I mean true cacti and although I also grow other succulents they are not my subject for today.
Unfortunately the Cactus Shop lumps cacti and succulents together.
Cacti are all members of the family cactaceae and include the very different desert and epiphyte species.
I discovered that certain cacti are very cold hardy indeed, coming from very cold places such as high in the Andes. Such habitats are either very dry in Winter or are under a blanket of snow. The difficulty of growing cactus in the UK is winter rainfall and high humidity. Worse the fluctuating conditions of moisture and temperature. If cacti don't like their Winter conditions they soon turn to mush!

The site that I chose was at the foot of the south wall of the house. Desert cacti must have lots of sunshine. I judged that the slight overhang of the roof would to a small degree shelter them from the worst of the winter rain. No matter that the site was a hardcore path! This was my most successful site but with hindsight had the soil had been a little richer but still very well drained, my cacti would have developed more quickly. Desert conditions although dry can be surprisingly fertile.
This really is quite deep hardcore covered with gravel. I do infiltrate a little soil when I plant
I have perhaps a dozen different cacti that have successfully over wintered outside in my garden. Some for several years now. Opuntias, the prickly pears have been the most reliable bankers. I emphasise that they need to be carefully selected. Those from the garden centre are unlikely to survive outside. I did however recently increase my stock of Notocactus leninghausii at Aldi!

Both the notocactus and the echinopsis are lifted into my cold greenhouse for the worst three months of the winter
Although I continue to grow many varieties completely outside, for others I have changed my technique. I bring them into my unheated greenhouse from mid December until the end of March. They love their nine months outside and grow better than any left in the greenhouse but by giving them this mid Winter protection I can grow a wider range of varieties that thrive.
I just dig them out in mid December using a hand fork or spade. Indeed because of their nasty spines anything other than my hands! I no longer plunge them in pots when I plant them and it is a very speedy operation to deposit them loosely in pots or plastic seed trays and to prop them vertical with extra soil when I bring them inside.
They will remain like this unwatered for three months. This notocactus is said to only survive four degrees centigrade of frost but it has survived two winters now
When lifted their roots will usually be wet. They will receive no more water until a week or so before they are planted outside in March. The time of planting varies a little with variety, nature of the season and whim. All I give them in Winter is an open unshaded position in my unheated greenhouse.

Unheated greenhouses in the UK are described as cold greenhouses. They will usually be several degrees above outdoor temperatures especially when the cold outside lasts for a short period such as a cold night.
Where there is continuous severe cold over long periods in Winter (unusual in these parts) then the cold does penetrate and the inside of the greenhouse will be similar to outside. In the exceptional Winter of 2010 my greenhouse temperature was – 15 degrees C for several days. The benefits at such times are wind protection and dry conditions. As there is no internal heat source in such circunstances bubble insulation is useless. Some of the truly hardy cacti withstand down to -20 degrees C.

Outdoor management
Cacti have simple requirements providing they have plenty of light. Good drainage is essential but ordinary well drained soil is absolutely fine. Don't waste money with cactus compost when any gritty mix will amend a heavy soil. Because yanking out once a year rather restricts their roots I do sometimes water them in dry spells in Spring. I also water the ones permanently planted under the roof overhang. I also feed them by top dressing with my usual NPK fertiliser - especially those growing in my hardcore!

Pictorial post

Readers will know of my admiration for hybrids! The fragile pads sometimes become detached and will root to rapidly increase clump size
The flowers of echinopsis are only open for a couple of days A huge range of colours are available
Brenda criticizes me when I let nigella seed everywhere! In this case she is right as it is important that cacti receive the maximum light. Any volunteers for weeding? Try a trowel
You might imagine fine hairs exacerbate problems of wetness. They seem to do the opposite
This opuntia permanently thrives well in full sun in ordinary garden soil.
Hardy opuntia associates with sempervivum, creeping thyme, dwarf dianthus and heuchera


New plants are easily propagated from pieces merely popped in! Most of my cacti are propagated inside in pots of my ordinary sandy garden soil
I later pulled the competing delosperma away
All my cactus have a gravel mulch which is said to be beneficial with regard to Winter wet
Rooted Maihuenia poeppigii cuttings planted to make a ground cover. It is the hardiest cactus that I know
This picture is for Po Simpson (the moonshot man). The name might suit him!

Silver torch or woolly torch cactus stands 10 degrees of frost but won’t stand Winter wet

Mistakes I have made
I originally bought about sixty different hardy cacti from a range of suppliers. All small plants. Cacti on the net are really quite cheap and I spent no more than £200. Some were no more than unrooted cuttings and as a Yorkshireman I only buy one plant of each!
I attempted to remember their names and failed.
I now regret leaving several outside for the first Winter when they were still very small. Most turned to mush. Larger plants seem to do better and before risking them I should have propagated spares in my cold greenhouse.

Although echinopsis need to be brought into the unheated greenhouse in Winter many fine varieties are available and I should have tried more. It’s not too late!

I did push the barriers with regard to sunshine and lost some to poor light. Only the maximum will do.

Although it was not necessary to amend my own sandy soil, I do recommend that gardeners with heavier soil amend it with grit and coarse sand. It is often beneficial to create a raised bed and plant on the plateau. I think had I planted in my sandy soil rather than retain my hardcore at the base of the house my plants would have faired better.
My only wall with the root overhang actually faces south/south west. A significant difference from south. We get superb morning light – a south/south east aspect would be excellent. Unfortunately it often clouds over by lunchtime. Worse a few of my shrubs cast a little shade when the sun is low in the sky. It is really important that cacti are in full sun.
I really feel at home on the range
More about my hardcore

I have added a link on how Edinburgh botanic garden grow hardy cacti in a simple plastic shelter

24 comments:

  1. Really amazing you can grow cacti outside, I'm sure the soil is far too wet here. I have a few ones in my conservatory I bought them as very tiny ones, but now after about 40 years they have grown rather big and they are difficult to handle. When I was young I was an Epiphyllum collector until the heating fell off in a harsh winter......

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  2. Well done on keeping them so long Janneke

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    1. roger , please tell me the name of the cactus in the second picture down . bottom right . with the big spikes

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    2. I think it is cylindro-opuntia imbricata

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  3. To be frank Roger I would only put cacti outside to kill them and you are telling me that this is not always possible! In the same way as my first love alpines, it is not the temperatures, as you know even deserts have massive diurnal ranges, it's the damp. I think we make a big mistake thinking that more exotic plants such as cacti or for that matter orchids are much different from the more familiar things we grow.

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    1. I think I detect you don't like cacti very much Rick!
      Are not some cacti alpine?

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  4. Thanks a million for all the good info. Really helpful. Soo much appreciated.

    All the best. Adrian

    P. S. Loose the background on website. Really hard to read :) no hard feelings.

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    1. Not sure what device you are using Kayzen but it always is clear to me.
      Anyone else with Adrian's experience please let me know.

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    2. Will consult my betters Kayzen!

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  5. Can I ask for some advice? I kept my cacti and aloes outside all yer in a custom made greenhouse. Last week I took them inside say about a week ago. Now would like to take them back to the new greenhouse I built. Will it kill them it is about 3-6 degrees at night here in London.

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    1. The cacti I have written about in this post have been chosen as hardy ones - at least standing down to -5 centigrade and those permanently outside much more.
      An actual temperature of 6 is fine for many cacti but it is the minimum later you have to consider

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    2. Built a greenhouse and will buy a heater :) don't wanna risc it. Will post a photo of my collection

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    3. Yes a normal collection should ideally be always frost free.
      It is very difficult for small heaters to hold temperature on a very severe frosty night but usually with cacti all is well!

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  6. too much rain here methinks (Scotland) but loving your cacti, I would consider moving to Tenerife to have some of their specimens in my garden but my OH would poo poo that idea

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    1. The 'hardy ones' would love your long summer days but not survive your long Winters!
      I imagine there is plenty of scope if you have a cold greenhouse to bring them in in Winter for perhaps four or five months where if completely unwatered they would be dormant.

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  7. our garden was recently washed away by the river. a new retaining wall was built and backfilled with 3" clean stone hardcore - some 20ft deep!!! and 30ft by 20ft on plan. we were going to just put flower boxes out but having seen you article I wonder if it would be suitable for Cacti?

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    1. Perhaps yes provided it is very sunny. My cacti in my hardcore area do have a soil when the roots grow down deeper below it and your cacti would need a soil as source of nutrition, You might put cacti in say a foot or more deep gritty potting compost on top of your hardcore which might be perhaps infiltered with soil at the top?

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  8. Good interesting read. Now working on a few ideas.

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  9. I left some cacti outside years ago to die, as my young daughter kept getting "spined". However they survived happily, left alone on their windowsill, even under thick snow, and are still going strong years later, and looking much better than when they were kept indoors. I have quite a few new ones since then. They stay outdoors through the summer. I bring them in for the winter but they don't seem to like it much. If you don't know their names, is there a way of telling which kinds are more likely to survive outdoors through the winter?

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    1. By inside I assume in the house and they won't like the heat. The poor light should matter less if they are completely dry and dormant and on a windowsill and you do as I do and keep them outside for eight months or so for the rest of the year
      If you don't know their names and have bought them at a gardening store you will have no idea of their hardiness unless you can guess the type and search google images.
      The best I can suggest is to leave them on the outside windowsill and see how they respond You can test them to destruction if you are not really bothered or if not watch them carefully for stress and if they show it bring them inside!
      I presume you don't have a greenhouse - perhaps a cold garage or shed window?
      You can buy small hardy plants very cheaply if you search the net for 'hardy cacti'

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  10. Very interesting we have a raised bed with a small pond which we will relocate when we have building work done, we are then thinking of turning this area into a cacti garden it gets full sun is sheltered from wind and we are three miles from the seafront at skegness, I do have a greenhouse to move any into for the winter I like the barrel type cactus 🌵 are there any of this type that would be any good for my site great blog thanks xx

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    1. Echinopsis responds well to my three Winter months in the greenhouse technique as does the golden torch and silver torch cacti (both illustrated) We had a very wet dull spell this summer and some of my echinopsis browned and I pulled a few out. Fortunately it had lots of pups. There is a wonderful range of echinopsis flower colours and they flower every year

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