By Carl Wilson, Colorado State University Cooperative Extension, Horticulture
Walls of Water are useful devices to extend the growing season for tomatoes, peppers, eggplant and other warm-season vegetables.
The channels of water in the sides of the plastic cone absorb heat from the sun during the day and radiate it back to the plant growing in the cone at night.
This provides an even greater benefit than simple frost-protection covers that do not store heat. While considered most useful during the cold weather of April and early May, this year they have been beneficial well into June. June night temperatures have been in the 50s and even dropped to 40 degrees along the Front Range. Chilling, not freezing, is the concern with warm-season vegetables at these night temperatures.
Tomatoes are subtropical plants that prosper in a uniformly moderate temperature range of 65 to 85 degrees. With chilly nights, plants often turn pale green or yellow, and leaves show purple veins. Growth is slow to nonexistent.
The pale color is a symptom of plants that are struggling physiologically and not taking up or using nitrogen well. The purple leaf veins reflect the plants' inability to take up phosphorous from the soil under cool temperatures, even though the quantity of phosphorous present is adequate or even high.
While a light application of fully soluble fertilizer may be somewhat useful, the real problem is cool temperatures, particularly night temperatures.
Plants grown without the benefit of a night heat source will remain set back for weeks, even after the weather finally turns warm.
Until night temperatures are consistently above 55 degrees, the Walls of Water are providing an appreciable benefit to your tomatoes, and you should consider letting them remain around your plants. Also be careful not to overwater plants, as cold and wet conditions are worse than cold and moist. Carefully dig down around plants to check soil moisture before watering.
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