Mr Frost has been visiting us a bit lately and while the kids love the sprinkling of white flakes over the back lawn and watching the ice melt slowly, it makes Tim and I very nervous.
Growing avocados trees in our climate has many benefits in terms of producing great quality fruit and lack of pests and diseases, but it also comes with risks, one of them being frosts. Frosts are not an avocado tree’s friend and they are one of our tree’s biggest threats, so this time of year is always a little bit anxious for us. There’s lots of checking of the weather forecasts, frost fan maintenance and seaweed sprays.
To protect the trees from frost as much as we can we have big frost fans which soar 11m into the sky. They have 2 large blades which are 5 ½ metres in diameter. The blades spin like helicopter blades and rotate around on their axis to move the air and to stop the frost from settling on the trees. We have three fans, each one covers a 6 ha radius.
The fans are set on a temperature sensor and they automatically come on when it gets below 0C. It’s all very techno these days and Tim has a special program on his phone so that he can see a satellite image of the orchard and each fan with the temperature reading at each fan and he gets alerts to tell him when each fan comes on or if there are any problems with them.
Basically the fans work really well as long as there is warmer air at the top of the tower. The fans work by mixing the warm air up higher which is generally about 4 or 5 degrees warmer than on the ground and pushing it downwards. As long as these conditions are right and the frost fans do their job, the big avocado trees can tolerate down to about -4C and the baby trees down to about -2C.
If the trees get frosted, it’s pretty serious. A severe frost can cause damage to the fruit on the tree and if it’s severe enough it can also cause the fruit to drop off.
If the frosts are late in winter it can also affect the emerging flower buds which will reduce the fruit set for the following season.
Fixing the frost fan
Last week we had a bit of bad luck to go with a pretty bad frost. First of all we had ants in one of the fan’s control panels, which meant we couldn’t set the temperature properly. Then Tim fixed that and the same fan “did a clutch”. Not great when a -2 frost was forecast for that night and there was no chance of getting the frost fan mechanics up to fix it in time. It ended up getting down to -3.3 that night. Luckily it was the fan that covers the highest part of the sand hill and the mature trees and we seem to have mostly got a way with it. We have had some fruit drop and some fruit damage but at this stage it looks like the flower buds are OK as they are not really emerging yet. So it’s not too bad, thankfully.
Managing frosts is just one of the many risks we have to manage on the farm and although it can be stressful, to us it’s just part of running the business. If you’re a famer you know there are risks and it’s about managing them as best you can. People often say “why would you be a farmer, when you have no control over the weather” and I always think, “well, that’s just part of the challenge”. All business have risks, all business face challenges and you can’t control everything and that’s the fun of it!