Growbag Blog

Will they check out if not hardened off?


A few years ago the English wine industry was at serious risk of losing 75% of its multi-million pound harvest this year because a -6 frost in the south of England in the last week of April destroyed the buds.  The ones above, snapped by Laura’s husband Tim, certainly took a direct hit. It was quite a sight to see acres of hillside vineyard lit by hundreds of burners that particular night in a desperate attempt to try and raise the temperature a degree or two and save the crop.
That late deep frost damaged a lot of new growth over in Normandy too – hydrangeas, persicarias, aloysia, a mulberry tree, even some roses – all looking like they had been scorched by a blowtorch or Nicola Sturgeon’s views on Brexit.  They’ll recover, but what wouldn’t have survived were all of those tender and half-hardy annuals of which so many billions are sold every year.

Hesperis matronalis

There is a bind here.
Cheap route: seeds and plugs, but you MUST have the space to pot them on and especially ‘harden them off’ – acclimatize them to the great outdoors until there is no chance of frost (mid-May with us, probably mid-July with Caroline!)
Hedge fund manager’s route: buy big ready-grown plants late and stick them in the garden.
I don’t have a greenhouse but I do have a sunny room with wide windowsills, and one of those small stand-up jobbies with four wire trays and a very tatty plastic cover for the hardening-off process. So, probably like many people, mine is a ‘some-and-some approach’ : annuals, a bit of veg and a few perennials from seed, other things mostly as cuttings, plugs and plants. So may beautifully delicate plants are much tougher than you imagine – who would have thought Louise’s Great Plant this Month could withstand frost? but my dilemma remains – how big do my teeny-weeny Hesperis matronalis seedlings have to be before I can kick them out to make space for the tomato plants?


On the morning of the fateful frost in Sussex we were setting off for the Scottish island of Islay. Elaine delights in pointing out how wet and windy it is in the Hebrides, compared with her beloved Normandy – fair play – but it also basks in the Gulf Stream, so there were no frost blackened shoots to greet us there. In fact it was so balmy then when Caroline came across to visit and announced loudly at breakfast that it was national Naked Gardening Day we all felt quite nervous…..
Now back in West Sussex I, like Elaine, only have the energy and space to cosset a few half-hardy specimens from seed. This year I have gone for Cosmos (always Cosmos) ‘Antiquity’,  Nicotiana mutabalis, as it seems to be a hot ticket at the moment, and an old favourite Cerinthe major ‘Purpurascensso I can watch the bees visiting – it’s not known as honeywort for nothing.

Cosmos ‘Antiquity’

My rule of thumb is not to plant out these welcome sub-tropical immigrants until the night temperature hits some double figures; they originate from countries such as Mexico, South Africa and the Mediterranean and although they may survive if planted out early, they will not thrive until the weather starts to feel a bit more like home. But I think Elaine can show her Hesperis seedlings a bit of tough love, they are European natives and can cope with a bit of a bit of battering from an East wind in spring.
The extent to which you need to harden them off before planting depends on how much heat and warmth you have given them thus far, and how cleverly you can capitalise on the miraculous natural shift in the weather pattern that takes place in May, as perilous frosts and drying winds give way to wet and warmth. Get it right and the final weeks of May can be some of the most exciting in the gardening calendar. It’s no surprise that Chelsea Flower Show is always staged in the last week of this month. I wonder which Chelsea growers have got it right this year?


Yes I can only guess at the headache those Chelsea people are enduring. I suspect few were minded, psychologically or demographically, to get involved in Naked Gardening Day but people on my favourite Facebook forum ‘Gardening UK’ looked great in their birthday suits.  For brother-in-law Tim’s sake I kept my clothes on but raised the topic of national celebrations because Laura went all Jeremy Corbyn when she heard about his plan for four extra public holidays. I reminded her we are already very unproductive in the UK.

Cold, windburnt and bitterly fed up, my stressed sweet peas

If we’re relying on my contribution of course, the failure of wine harvests the world-over is probably going to be helpful, but who can blame me? The prospect of us reaching double figures at night in Scotland are slim, and a cold, dry wind has relentlessly piled on the guilt for evicting my sweet peas from their cosy greenhouse billet to the frozen pampas outside. I actually turn my head when I pass their limp, grey outlines, but honestly I just don’t have time for this gradual process. Neither do I have the same £250,000 responsibility for producing perfect plants which Chelsea exhibitors are currently shouldering.
I did consult the Royal Horticultural Society website for ‘hardening off’ advice. They started off with a great deal of transferring plants to cold frames for short daytime periods and choosing overcast days; then worked their way down through ‘making do’ with south-facing walls and simply relying on fleece and, as though finally identifying me as their most hopeless customer, concluded, “Covering with an old curtain can protect from sudden sharp night frosts.”
Could still be handy advice for the vineyard owners.






By the3growbags

We're three sisters who love gardening, plants and even the science of horticulture but we're not all experts. We'd love everyone even remotely interested in their gardens to be part of our blogsite.

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