Greenhouse - Effects on Crops When Considering Growing at Lower Temperatures II

Although prices have dropped recently, continued high energy prices are prompting many greenhouse growers to consider lowering their greenhouse temperature setpoints to reduce their monthly heating costs. This is the second post on the subject taken from an article from the Michigan State University Greenhouse Alert Newsletter.

Cold-tolerant and cold-sensitive crops

The reason for the difference in how temperature influences crop timing is related to the base temperature of a plant. Plants with a low base temperature can be considered “cold-tolerant plants.” Those with a high base temperature can be called “cold-sensitive plants.” Cold-sensitive plants are more sensitive to a lower greenhouse temperature than cold-tolerant species. There are also plants that fall between these categories (base temperature between 39°F and 46°F), such as red salvia. All plants respond to temperature during all stages of development. For example, seedlings of Salvia ‘Vista Red’ grew faster as temperature increased from 57 to 79°F (14 to 26°C). At these temperatures, plugs grown in 288-cell trays took approximately 6.5 weeks to finish at 57°F and about four weeks at 79°F. Plants also respond to temperature during the finish stage. For example, under the low light conditions of winter, time from transplant to first flowering of Salvia ‘Vista Red’ took 12 days longer at 63°F than at 73°F.


Temperature effects on plant quality

For many crops, plant quality at the same stage of development increases as growing temperature decreases. If plants are grown at similar light intensities but at different temperatures, marketable plants grown at cooler temperatures often have thicker stems, greater branching, more roots, and more, larger flowers. Exceptions to this are plants that grow best in warm conditions, such as hibiscus. Therefore, one of the benefits of growing at cool temperatures is that overall plant quality could be improved even though crop timing is delayed. However, remember that some plants, especially warm-season plants, can experience chilling injury at cool temperatures.

Adapted from "Temperature effects on crop timing and plant quality" by Erik Runkle,Horticulture, in the October 28, 2005 edition of the Michigan State University Greenhouse Alert Newsletter.