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You can grow tomatoes even in cold weather. A farmer in Zimbabwe, Mr. Francis Handwa, uses cooking oil or milk bottles filled with water to keep tomato plants warm. This is a good alternative to covering tomatoes if used bottles are easy to get. Here is how he does it.
Francis fills cooking oil or milk bottles with water until they are three quarters full. While the plants are still young, he places the bottles upright on the ground among the tomatoes. He places one bottle beside every third plant in every other row. He makes sure that the neck of the bottle appears above the plants. When the plants get taller than the bottles he places stakes beside the tomato plants. He hangs a bottle on each stake with a string. The bottles hang 10 centimetres above the plants.
When the temperature drops below freezing the water in the bottles freezes. The tomatoes stay frost free even though the surrounding grass and shrubs are covered with frost.
Mr. P.R. Makaya, an expert on fruit and vegetable production in Zimbabwe, explains why the water in the bottles freezes while the tomatoes are not attacked by frost: “When water has things dissolved in it, it freezes at a lower temperature than when it is pure. The water in plant cells, tomato cells in this case, contains dissolved salts. But the water in the bottles is pure, or at least has much less dissolved matter. In frost conditions, pure water freezes earlier than water in plant cells. So in the morning you find the water in the bottles is frozen. When water freezes it releases a lot of heat. The heat released when the water in the bottles freezes keeps the air around the tomatoes warmer than the surrounding area”.
Here are some other ways to protect tomatoes from frost.
This script was prepared by Livai Matarirano, Coordinator, Farm Radio Network (East and Southern Africa), c/o Africare, P.O. Box 308, Harare, Zimbabwe.
This script idea came from Takaniso Nyoni, a trainer at the Wensleydale Farmer Training Centre, Zimbabwe, who learned the technique from a farmer during a horticulture course at the centre in 1994.
Dr. Anne D. Turner, Cornell/CIIFAD Fellow, Crop Science Department, University of Zimbabwe and Mr. P.R. Makaya, Agricultural Extension Specialist, Department of Agricultural Technical and Extension Services, Agritex, Zimbabwe reviewed this script.