Merici College Year 10 students Katelyn Andrews and Lisa Barnes with tomato seedlings in the school's green house. Photo: Jeffrey Chan JCC
Producers and backyard gardeners around Canberra were holding their breath on Tuesday morning as the second-coldest October night on record left frost over parts of the region.
Any cavalier tomato growers looking for an early harvest could have been hurt after the temperature dropped as low as minus 2.6 degrees at Canberra Airport – the coldest it’s been in October since 1957.
Conventional wisdom in Canberra is that tomatoes should not be planted before Melbourne Cup Day for this very reason – market farmer Michael Plane of Allsun Farm at Gundaroo said tomato crops can be ruined by an overnight freeze.
For big tomatoes like these market farmer Michael Plane recommends growers buy their seedlings in Canberra, as they're likely to be more hardy than plants grown in Sydney. Photo: Getty Images
‘‘Because the plant leaves have cells which are full of fluid water, when they freeze, when something freezes and then defrosts, it actually expands and breaks the cells, and the plants don’t thrive,’’ he said.
‘‘A good time to plant tomatoes is when you can be sure the last frost has gone. And that, nobody knows.’’
Frosts aren’t uncommon in October and can persist into November, but, according to forecaster Rob Sharpe from Fairfax-owned Weatherzone, a night this cold halfway through October – and exactly halfway through spring – is rare. He said the freezing start to Tuesday had its genesis in the gusty system that swept through on Sunday night.
‘‘The reason why it got so cold [on Tuesday] morning is because we had such a cold air mass come in behind the cold front that arrived the other day,’’ he said.
‘‘The really cold air mass with light winds and clear skies allowed whatever heat was around to rise and the cool air to settle near the surface.’’
When it came to tomato-killing frosts, Mr Plane said gardeners had two main defences if they were planting out early in the hope of a Christmas crop. The first was to check weather reports every day and cover seedlings with plastic pots or milk bottles when cold nights were forecast. The second was to use seedlings that had been raised andhardened locally, and were accustomed to the Canberra climate.
‘‘My advice to anybody buying any tomato seedlings in Canberra is to make sure they’re locally grown,’’ he said. ‘‘If they’ve come from Sydney they’re not likely to be particularly hardy.’’
This year students at Merici College have overcome both those issues, and have raised about 600 tomato seedlings sowed from seeds in the school’s greenhouse – keeping the plants frost free, but still familiar with local conditions.
Under the guidance of sustainability teacher Fiona Buining, students planted 15 varieties of tomatoes over the past couple of months, and planned to sell most of the seedlings at an open day at Mr Plane’s Allsun Farm on the weekend of October 26 and 27. ‘‘If you grow them where you’re going to plant them, they’re going to be quite adapted to the environment,’’ MsBuining said.
Year 10 students Katelyn Andrews and Lisa Barnes have been working three hours a week in the school’s greenhouse and gardens, planting the tomatoes, and both said they planned to put their knowledge to use when they left school and started their own vegie patches.
‘‘Plant after Melbourne Cup,’’ Ms Andrews advised. ‘‘And don’t touch the [stems] while planting.’’
It wasn’t just the tomato growers nervously watching the temperature gauges overnight either. Vintner Ken Helm of Helm Wines said at least one of his vineyards recorded temperatures below zero, but he hoped most escaped any serious frost.
‘‘At this stage I’m saying we’ve had minimal damage, but we won’t really know the full extent until I get back tomorrow. It takes around about 12 to 24 hours to manifest itself,’’ he said.
While grapes were susceptible to freezing temperatures, Mr Helm said most vineyards in the region were on hillsides that avoided the worst of the frosts. He said a full moon at the end of the week threatened to bring another sub-zero night.
‘‘We always expect at least one, maybe two days like that. So, hopefully that was the one. It is a nervous time of the year for us, but after 40 years you get used to that.’’