Frost Facts and Frost-Proofing Tips

All the old-timers in the Nelson Lakes area, where I live, are predicting a harsh winter this year.

They’re saying the conditions are ripe for a repeat of the Polar Event of early June 2008, when the power was off for 10 days and everyone packed the contents of their freezers in the metre-deep snow.


This was preceded, they say, by a long, hot, dry summer and a mild, wet autumn. We’ve definitely had those. But apart from a couple of light dustings on the nearby ranges and a few very mild frosts, there’s been no real hint of impending winter . . . yet.

Fewer frosts doesn’t mean they’re less severe

In its 2007 report summarised on the NIWA website, the Intergovernmental Panel on Climate Change (IPCC) said New Zealand is “virtually certain” (i.e. more than 99% probability) to experience a reduction in snowfall and frosts this century.

However, in that same year, the Insurance Council of New Zealand logged more than 2,300 damage claims totalling just under $8 million across Central Otago, South Canterbury and Southland, following severe frosts over 7-9 July.

So while IPCC talks about increased pasture growth and fewer lamb mortalities as short-term benefits of fewer frosts, it doesn’t necessarily follow that the frosts we do get will be milder.

Frost types

Radiation frosts are the most common frosts in spring and autumn and only occur at night. They’re caused by loss of heat from the earth into the sky and are associated with clear, calm conditions. The coldest air is closest to the ground.

Advection frosts are caused by freezing air that has come from somewhere else, such as snow-covered mountains or polar fronts. These frosts can occur day or night and are usually associated with windy conditions. The air temperature decreases with altitude. Advection frosts are most common in winter.

Hoar frosts are those beautiful frozen sculptures you sometimes see hanging from tree branches and fencing wire in Otago. Black frosts are caused when air temperatures drop below zero but there’s not enough moisture to form ice crystals. The resulting frost damage causes vegetation to turn black. Window or fern frosts are formed by cold, moist air on glass.

Frost-proofing tips

• When laying new pipe, take ground temperature extremes (heat and cold) into consideration. Expose as little pipe as possible to the air.

• Get frost protection kits for your water tanks.

  • Ensure taps and pipe fittings don’t leak and have air-tight seals.
  • Insulate valves and exposed pipe.
  • Disconnect hosepipes from taps. If water in the hose freezes, it will expand into the tap and then into the pipe, possibly causing it to rupture.
  • Check exposed pipes regularly. If they do freeze, they may split and then cause flooding when they thaw.

Preventing stock water from freezing

I’ve read all sorts of grassroots suggestions on this subject but haven’t tried any, so I can’t vouch for their effectiveness.

The first one on the list definitely makes sense:

  • Site stock water troughs facing north and out of shadows. Use black troughs (understanding that they’ll heat the water in summer). Fence-hung troughs may be slower to freeze than those sitting on the ground.
  • Float a volleyball or similar on the water. Its motion on the surface could be enough to stop the water freezing.
  • Pack fresh manure around the sides of the trough and then cover it with black plastic. The manure heats as it decomposes and prevents the water from icing.
  • Add molasses mixed with warm water into the troughs. The idea behind this is that sugars in the molasses act as an antifreeze, so although the water may go slushy, it won’t freeze altogether.