Winter protection

Imagine: it’s September and fast approaching that time of year when we Exoticists start getting fidgety.  Michael Fish appears on our TV screens and we start taking less notice of his jacket and more notice of the spreading blue patch on the chart behind him.  The nemesis approaches: frost is on the way.

Will this year be 'The Year'; the infrequent but dreaded arctic winter when our gardens will be devastated by weeks of sub-zero temperatures?  Is there anything we can do to keep our botanical babies safe?  Thank Heavens the answer is a resounding ‘YES’ and for those readers for whom that feeling of paranoia is new and unnerving, here are a few pointers to ease the unease.

Facts and figures

Most importantly, get to know the weather where you live.  The Met. Office has its spies in most areas and the information is freely, if not easily, available to personal callers at their library in Bracknell.  Unless you have a realistic idea of how cold your locality is likely to get, you are always going to be heading into winter blindfolded with fingers crossed.

Also get to know the plants and their lower temperature tolerances.  Often these are well documented, either from having been grown in this country or abroad; sometimes it isn’t but a little research pays dividends.  Though occasionally it is fun just to try. 

The big ‘however’ is that we don’t necessarily only want to grow plants that will survive our coldest winters; in fact it is half the fun of exotic gardening to grow lots of plants that we know aren’t totally hardy but, using our skill and guile, can be nursed through the forbidding freezes.

Insulate and circulate 

I have one rule when it comes to insulation material: it MUST allow air to circulate and moisture to evaporate.  The material can be a temporary covering during cold spells or left in place throughout the winter but either way should be porous.  I find the most convenient material is horticultural fleece, which is available from most garden centres.  Keep a large roll of it in the shed; it is inexpensive, light, easy and may just save a treasured plant as a double layer will give around two degrees of frost protection, plus stop physical freezing damage by taking the brunt of the surface ice formation. 

Bubblewrap is often advocated as a useful material for protecting your plants, but in my experience by spring you will end up with a well-protected and warm heap of mush.

 The following is a guide to the best ways of protecting plants, lumped together by type.

 Bananas

 There are 3 main groups of bananas: musella, musa and ensete.  Musella lasiocarpa can be treated as musa and the musas in question are Musa basjoo and the new kids on the block; Musa sikkimensis, Musa ‘Rajapuri’ or indeed any of the other novelties that are being whispered about excitedly in dark places.  Of paramount importance is keeping the underground portion from freezing; heaps of autumn leaves piled over the root zone will usually do the trick.  This is as far as it needs to go – trunk protection isn’t necessary - and in the colder regions is the most realistic option.  I have spoken to a chap in Montreal, Canada that snugly insulates his Musa basjoo through their -26°C winters and still gets a 3m high plant by the autumn.

However, to enjoy the spectacle of flowers and get the tallest possible plant you will need to keep at least some of the trunk.  The sad leaf tatters spared by autumn winds will be clobbered by the first frost; this is time to remove them cleanly from the trunk leaving the desired height remaining.  And that is as far as you lucky fellows in the balmy southwest or central London often need to go, but most of us will need to insulate most winters.  Protecting banana stems is a bit of a palaver so it is probably best to do something that will remain in place all winter; this means you will be looking at it for several weeks and need to be happy with it’s appearance. 

Small plants are easily protected by placing a chimney pot over them and covering the top with a tile - colder regions may like to add a stuffing of straw.   A stage on from this is to use terracotta chimney flue liners.  These are neat round or rectangular sections that stack together; they are easy to manage, easy to lift over a tall trunk (try negotiating a 2m chimney pot on top of a set of wobbly stepladders….) easy to pack with straw and can be added to as the plant grows each year.  Unfortunately they are also expensive. 

Larger, multi-stemmed plants present something of a dilemma – do you protect the stems individually or collectively?  There are many inventive and creative solutions to collective protection – from the highly effective wooden pallet house filled with straw to elaborate imitation huts of bamboo screens disguising a chickenwire cage similarly stuffed – your imagination and available time are the only limits.

Individual stems can simply be bandaged with horticultural fleece or hessian - effective though not necessarily the beauty-prize winner.  I personally use large diameter plastic drainage pipe which is twin-walled giving good insulation, perforated allowing air movement, is easy cut to the required lengths and light enough for long sections to be lifted over stems.  These are then lashed together for stability and the tops covered with plastic sheet to prevent rain entering.  The result looks a little like the Manhattan skyline but in a surreal way almost sculptural.  

Ensetes are so tricky to overwinter in situ that I deal with them separately.  That is a lot on bananas, but the principles involved can be applied to just about anything else.

Palms

Palms are better if only given protection when they need it.  In early winter before the weather deteriorates greatly, bash in three stout canes around your more tender palms and then wait.  Keep an ear to the weather forecasts and when a cold spell approaches, tie up the leaves with twine and bandage around the canes with fleece.   

When the cold snap passes, unwrap and let the fresh air and sunlight refresh your palm until the next cold spell.  A popular trick in the US is to wrap outdoor Christmas tree lights around the palm before bandaging with fleece; each of the small bulbs emits a tiny amount of heat which, collectively, is enough to give a couple of degrees of additional frost protection.

Treeferns

There are a lot of conflicting opinions about hardiness of Dicksonia antarctica; after exhaustive research I conclude that wherever they originate, be it Tasmania, Victoria or anywhere else, they are all of similar hardiness down to around -10°C.  The protection I would give the plants down to this limit is what normally happens anyway – autumn leaves fall in the crown of the plant and keep the growing point safe.   Plants in cold or exposed positions will lose older leaves but D. antarctica isn’t harmed by this.  Below this limit, or if you are growing more tender treeferns such as Dicksonia squarrosa or cyatheas in areas below their tolerances, you will need to protect their trunk in some way.  I have done this by wrapping with loft insulation – an initial layer of fleece facilitates clean removal – but it is important to keep the trunk watered during drier spells.  In some cases e.g. Cyathea medullaris, it may be necessary to try to protect the leaves as well as annual defoliation sends the fern into a gradual decline; again, this depends upon your local conditions and the particular fern.  

Succulents

Winter protection of succulents is more initial soil preparation than subsequent protection.  It is wet, not just cold, that will kill them off so try to provide every opportunity for moisture to disappear rapidly.  Make the soil VERY free draining – I use a ratio of around 1:3 of soil:grit and ensure good air movement to evaporate moisture.  I have never tried, but I am told a soaking of fungicide in early winter can be insurance against rot.  Physical protection from the rain is another worthy measure; I use small plastic domes that are on the market pegged down over the plants.  

The larger ones have air vents at the top, which allows evaporation; smaller sizes are best removed on sunny days.  These domes have the additional advantage of heating up like mini-greenhouses.  A friend uses small umbrellas over larger individual plants with some success, though visitors must leave with some searching questions. 

Dig and store

I am lumping together in this section anything that is bedded out for the winter and dug up for winter storage and include things like cannas, gingers, aroids, and ensetes.  Obviously there are many parts of the country where you can get away with leaving some of these outside all year, but most of us have to dig and store.  There are 2 main methods depending upon whether you have any heated glass or maybe lots of windowsills.  If you do, and don’t mind indoors looking like Borneo for the winter, pot the plants up and keep them ticking over for winter; cannas can be kept growing most of the winter like this, so can the more tender gingers and ensetes (though these require rather large windowsills).  Aroids such as Colocasia esculenta ‘Black Magic’ and other darker leaf variants are best kept growing in this way as they don’t seem to overwinter well when dormant.

Method 2 is simpler but not totally foolproof (the voice of an experienced fool…) so be prepared for some losses.  Once the leaves of the plant in question have been blackened by frost, dig it up, shake off all the soil then cut the leaves and roots off.  If you can, lay the plant on its side in an airy garage or shed to dry off completely for a week or so, then dust with fungicide or green sulphur powder.  Cannas and gingers are best stored in vermiculite or peat that is kept BARELY moist; overdo it and they will rot, too little and they will dry out.  Aroids are better kept drier, just leave ensetes to stand in a corner like the naughty plants they are.  All these should survive if kept frost free with air circulation.

Plants that have been grown in tubs for the summer are in some ways easier; just take the plants, pots and all, into the garage/shed and allow to dry out.  Occasionally give a light watering to prevent complete dehydration of the dormant plants but again don’t overdo it.  When temperatures and light levels begin to increase in spring the plants will wake up, start to put out some new growth and will then be ready for re-potting, dividing etc. thus starting it all off again.

So don’t let the onset of winter dampen your spirits – insulate and circulate!

Text ã Paul Spracklin June 2000 , based upon an article published in Exotic and Greenhouse Gardening winter 2000

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