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Getting tender plants through the winter

Thursday, 8 November 2018  |  Admin

After the last winter's long cold snowy spell we are all probably prepared to deal with another spell of cold weather, which which I’m sure we are all hoping won't materialise. Many parts of the country have already experienced frost or snow and most of the really tender tropical plants should have been moved indoors by now or protected outdoors. You only have to follow a plant related group on Facebook to see how inventive people are when it comes to keeping precious plants over the winter, the attic, kitchen, nothing is out of bounds to the lover of frost-tender plants. Looking around our house I'm sometimes reminded of the line from a Flanders and Swann song:

'The garden's full of furniture ...the house is full of plants'!

Having stowed as many plants indoors, how many of us will admit to getting up at 3 am and going outside in the freezing cold with a torch to check the greenhouse heater, or to tuck an extra piece of fleece over a plant?

Some points to ponder when it comes to nurturing frost-tender plants, factors which can make the difference between success and failure. 

  • Get to know the micro-climates in your garden - favoured spots for over wintering plants are the base of a south-facing wall, but any where that will afford some protection against rain and snow will help. My tender Agapanthus survived the winter 2017/18 in a dry area under a thick evergreen hedge with an overhang of Ivy. Dry plants survive better than wet plants
  • Feed plants with a high potash feed, rather than one high in nitrogen, 
  • The age of plant will have a bearing on its chance of survival, take Mandevilla laxa for instance, known to be somewhat tender. The plant we had at our old nursery site got to be 10 years old, and survived a cold winter down to minus 10. It was severely cut back but new growth rapidly appeared in spring and it flowered profusely the following summer. Sadly, we had to leave it behind when we moved. 
  • Insurance, precious plants spread around - we tend to do this a lot at the nursery to make sure we have stock to propagate from.
  • Cover with several layers of fleece or netting, but not under pot
  • Realise that a long spell of minus 2 may well do more damage than a short sharp minus 10. Charlie, our mad springer spaniel, unfortunately no longer with us, put this to the test one very cold winter. He managed to attach a piece of a Selenicereus from our greenhouse (a tropical cactus which I'd always assumed to be very tender) to his fur then roll in the snow outdoors, where it became detached. The temperature that night dropped to minus 10 or lower, so I was rather surprised when the rock solid cutting I found the next day, after being gently thawed, didn't turn to mush but started to grow! 

At our latitude in the UK winters can be long and, to us, cold, but they would be colder if it weren't for the gulf stream, which, believe it or not, keeps us warmer than other parts of the world at the same latitude. In Suffolk (latitude 52 degrees north) we are classed as being in USDA (US Dept. of Agriculture) zone 8b which means we can expect lows of around minus 9 - 10. We were in N Carolina a few years ago, where in theory the temperatures can be lower, BUT due to the lower latitude (just 35 degrees north) the winters are much shorter, and low temperatures don't last as long. Someone we met over there was very concerned about her Camellias, her comment was something along the lines of 'We get minus 10 in January' (I nodded sympathetically).... 'but, gee, by February it's back in the low 20's !!' (I felt a slight pang of jealousy.)

Heating of greenhouses 

Strangely, the temperature in an unheated greenhouse can fall lower than that outside on a clear frosty night.  I won't bore you with the reasons, but be aware that such a structure won't keep the frost out without the help of a heater. Once you start heating, insulation in the from of bubble film or fleece is imperative if you want to keep your heating bills down. Bubble film is great but does produce a lot of condensation which can drip on the plants. We find a couple of layers of fleece are effective, with less of a problem with drips.  

Yes, a plant may survive, but if it's not going to flower or be productive , is it worth growing it. We have a number of plants which have proved that they can survive low temperatures, but struggle to put on enough growth for us to propagate from. 
Lack of day length

Forecasts - learn to out guess the forecaster, on numerous occasions the forecast has been for a cloudy night which will keep frost at bay, only for the skies to clear, the wind to drop and the temperatures plummet. 

Sometimes a plant will have appeared to survive the winter but then fades away when it attempts to grow away in the spring. 

We do need some cold weather though:

Seeds need frost in order to germinate, for example Primulas

Frost adds another dimension to gardens, picking out the detail of leaves and flowers that we might not normally notice.

Some of us might dream about global warming nudging our winters towards being frost free so that we can grow Bananas and the like outdoors year round. However, we should remember that many plants require a cold winter to become fully dormant so they can perform their normal growth cycle. Important food crops such as apples, have a 'minimum chill requirement' Without a certain length of time below a certain temperature they may fail to initiate flowers and fruit for the following summer:

Whether or not the climate is going to change in ways to significantly affect us as gardeners, the experts, and recent experience, seem to indicate that we should be prepared to expect to experience long spells of one type of possibly challenging weather pattern.