Manage the root temperature in growth bags for optimal growth

Root temperature does play an essential part in plant growth. It influences plant dry-mass, uptake of nitrogen, phosphorus and potassium. Root zone temperatures between 18–22°C lose less nitrate and phosphate through emissions¹⁾Miguel Urrestarazu, María del Carmen Salas, Diego Valera, Adrián Gómez & Pilar Carolina Mazuela (2008) Effects of Heating Nutrient Solution on Water and Mineral Uptake and Early Yield of Two Cucurbits under Soilless Culture, Journal of Plant Nutrition, 31:3, 527-538, DOI: 10.1080/01904160801895068. Reactions to root temperatures can be confusing. There is an optimum temperature for plants to grow. Plant growth is better at 25°C than 20°C and 30°C. Both the lower and higher temperatures decreased leaf area index of tomato plants ²⁾Hmiz, D. J. et al. (2019) “Effect of the Root Zone Temperature and Salt Stress on Plant Growth, Main Branches and Some Other Chemical Characteristics of Tomato Fruit,” 32.. 

It was found with tomatoes that phosphorus and potassium uptake increased with increasing root zone temperature. However, root zone temperature had no effect on the nitrogen content of the plant.

It is important to note that when the night temperature is higher than during the day, plant growth is adversely affected. It applies both to air temperature and root zone temperature.

The optimum root temperature for most sub-tropical crops (tomatoes, peppers and brinjals) is in the region of 25°C. Root growth stops at temperatures below 10°C. Lowering the temperature of the root zone to 15°C reduces the uptake of nitrogen, phosphorus and potassium, which caused some problems with fruit quality.

Lettuce gave excellent results with root zone heating with head mass, root mass and length increasing up to 30°C in the root zone.

The most vulnerable period during plant growth when heating the root zone is in the first two months of growth. Heating the root zone without close monitoring can cause the root zone temperature to increase above 35°C due to radiation. Care must be taken during this period, not to overheat.

Do not apply this technique should to closed systems since the danger of water diseases increases with increasing water temperature.

High root temperature with low light levels reduced flowering and fruit set under shaded conditions ³⁾A.GosselinM.J.Trudel. Scientia Horticulturae. Volume 23, Issue 4, September 1984, Pages 313-321.