Effects of Cool Temperatures on Tomato Plants

Often, our early-planted tomatoes have to endure some cool weather. Here's a bit of a review of the effects of low temperatures on tomato transplants.

Tomatoes stop growing, and are susceptible to chilling injury, at temperatures between 0 and 10°C (32-50°F). Chilling injury can show up after short periods of the lower temperatures or long periods of the higher temperatures and can cause:

• stunted growth
  
• wilting, surface pitting or necrosis of foliage
  
• increased susceptibility to disease
  

Low soil temperatures also stunt plant growth and prevent root development.

In addition, plants that are not actively growing would be expected to have a tougher time metabolizing herbicides. Cool soil temperatures mean that slow root growth also limit the plant's access to soil nutrients, such as phosphorus. Using a starter fertilizer with high phosphorus and a bit of nitrogen can help get the plants off to a better start in these conditions.

The combination of cool weather impacts can result in some poor looking plants, but the crop should recover when warm temperatures return. Plants that have been severely stressed, however, may be slow to resume growth and may have lost some yield potential.

Not all cool-temperature effects show up right away. Low temperatures experienced by the plant 4-5 weeks (!!) before flower buds are visible, can affect flowering and fruit set.

In tomato, freezing damage occurs at -1 to -2°C (28-30°F). It may be difficult, initially, to determine whether the growing point has been killed and damage may become more evident on the day after the frost.

Besides cool temperatures, young, early-planted transplants may also experience wind whipping, wind desiccation, and possibly sandblasting. Strategies to combat this include:

• setting the plugs sufficiently deep under the best planting conditions that you can possibly achieve
  
• using wind protection systems (cereal crop wind strips, cover crops, crop residue)

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