Strategies to reduce the impact of frost

Nari, Normal

The National, Tuesday October 13th, 2015

 Prolonged dry seasons eventually result in frosts, especially in high altitude areas. When there is frost, food crops are severely destroyed. Research undertaken by the National Agricultural Research Institute (NARI) has defined situations giving rise to frost, its impacts, susceptible areas, and how people can cope with it. 


What is FROST?

Frost is a term used to describe the ice formed from dew when air temperature gets too low. Frost can occur when cold air from the mountains settles into low-lying areas on clear nights when there is no wind. 

On the tops of high mountains, this can occur during the dry season and normally only when the weather has been very dry for a long period. 

During such times there are usually no clouds and wind in the night.

Clouds act like a blanket over the earth and stop it from getting cold. So frost does not occur when the weather or sky is cloudy. 

Wind mixes the air so that the cold air from the mountain does not settle into low places. Hence, frost does not occur when there is wind blowing.


Where frost is likely to occur

Frost tends to occur more frequently on flat land or in valleys at the bottom of a mountain. This is more common in high altitude areas where the average minimum temperature is usually below 13C. 

Higher up the mountain, while it is normally cooler, the cold air flows down to lower areas almost like water flowing down hillsides. 

It is only with severe frosts that there is much damage on the sides of hills. When this occurs, the damage is normally much less than at the bottom of the hill.

Reducing damage caused by frost

Local experience over a number of years should show areas where frost tends to be worse, and where it tends to be less severe. Steps should be taken to minimise damage by making sure susceptible areas are marked out.

  • Some gardens should always be planted in the areas where less frost damage is expected;
  • traditional practices of planting gardens in different areas of available land help to ensure some gardens will not be affected by frost.
  • gardens on good soil on the bottom of hills tend to produce more crops under normal conditions but can be more subject to frost.
  • gardens at the top of hills near the bush may not produce as well normally, but are less likely to be affected by frost.
  • gardens on hillsides tend to be less affected than those at the bottom of the hill. Though they do not produce as well as those at the foot of hills, they may be better than those near the bush at the top.
  • trees should be planted near gardens at the bottom of hills to help reduce the effect of frost.
  • a row of trees planted across the hill above the garden can stop cold air coming down. Trees planted across the hill but below the garden will trap cold air causing more severe frost damage.
  • trees planted on a hillside should have plenty of space between them to increase air movement and circulation. This means the cold air flowing down will mix with warmer air and reduce frost occurrence.
  • the practice of planting gardens between yar trees that have had a lot of branches cut off to allow light in should be encouraged. This also helps reduce frost by increasing air circulation.
  • thin layers of pitpit should be laid on top of sweet potato mounds and kept there until the frost season ends for plant protection. A thick layer would be better though it will need to be removed during the day to allow the leaves exposure to the sun. The pitpit can then be used in mounds for new gardens.
  • old corn stalks and bean stakes should be left in gardens to help protect sweet potato vines from being damaged by frost.
  • Few small fires should be lit in gardens to help reduce frost damage. When smoke rises, air around the fire is drawn in, causing air movement that disturbs the mass of cold air in the gardens. But, any fires lit will need to be managed very carefully, as frost and drought and extreme fire hazard go hand in hand.


Such steps should be undertaken in preparation for frost occurrence once a drought warning is issued. 

Frosts are associated with droughts due to the fact that there is less cloud cover both day and night with temperature that are high during the day and very low during the night.

Long term considerations would include planting trees round gardens at the foot of hills and above gardens on hillsides.

Work on frost tolerant crops at NARI’s Highlands Regional Centre in Tambul, Western Highlands, has identified certain crop varieties that can survive frost – wheat and Andean tuber.  

The category of frost during this year’s El Nino was mild to moderate as cabbages, brassicas, wheat and peas are still growing. 

Communities witnessed frost over four consecutive nights in mid August.

From a survey of sweet potato, Irish potato and brassica species in ten different farmers, there were 100 per cent damages to sweet potato and Irish potato in small to large gardens as ice frost spread and covered the whole garden.