Northwest Earth Institute

Winter has finally arrived and so have the frosts.  In the Upper Mountains we know it all too well; but in fact frost can happen anywhere in Australia even the tropics. The Atherton tablelands can experience early morning frost even when the daily Temperature climbs to 21ºC in winter. Sitting here, in mittens next to the heater typing away, I would be happy with half that warmth as the day progresses. And I have only to look out the window and see how the lettuce are huddled down and refusing to grow, as bigger leaves would mean frost bite.

So I have to concede that as we try and push the boundaries of what we can grow at our dizzy altitude, we need to recognise that for some plants protection will mean the difference between life and death.

By definition a frosty night is a “clear and still winter night where sounds seem to travel for miles and the earth beams its radiant heat into space... without a cloud blanket to keep any heat in, the moisture at ground level freezes and forms frost”. 

As the cold comes up from the ground the cells inside many plants freeze and burst as the water inside them expands to form ice.  Damage to the cells can also occur when the ensuing sun at daybreak melts the water so fast that the cells walls can’t respond quickly enough to these changes in pressure; in some cases the plant never recovers. 

In days gone by, farmers would light fires in their orchards to create an inversion layer of smoke to keep heat in, much as clouds do, or they would put on water sprinklers to  stop the frost forming. I have tried spraying my lettuce lightly to thaw then out slowly and it has seemed to work if I can get up and out early enough, and fortunately for me, spinach and kale don’t seem so sensitive.

For several years now I have potted some of my hardier veggies and rehoused them in a sheltered spot till summer, and then I plant them out again. In my case a hot house but prior to its purchase I would just bring the pots close to the house and make a cold frame using window glass as a cover. This way I manage to turn some of my annuals into perennials one of Bill Mollison’s concepts; capsicum and chilli seem to respond well to this treatment.

I have also  discovered that frost protection can be as simple as throwing a blanket over your plants or if you want to protect a plant for several years a simple structure can be built around it so that it can be wrapped in insulating materials. I have seen photos from Europe with trees shrouded in straw and bracken within a wire structure. I haven’t tried protecting mature trees but I have used home-made chicken wire cylinders covered in bubble wrap around my newly planted trees until they mature and become more frost resistant. I’ve been told that a ‘hat’ can be placed over it during the night and removed during the day, but I doubt I would ever remember... this works for container plants as well.

Lizzies cold frame              Wire structures over containers can be covered  

 Bubble wrapped cylinder covering lemon-grass       Rowe’s old hot-house

I guess the moral is that if the air is still and the sky clear, cover your frost sensitive plants; it is always better to be safe than sorry.