The Effects of DIF on Potted Foliage Plants

DIF

• Average day and night temperatures influence overall plant growth rates, with higher averages resulting in higher rates of growth and development. DIF, the difference between day and night temperatures, influences stem elongation. Dr. Royal Heins of Michigan State University pioneered DIF research and developed guidelines to implement DIF for successful greenhouse plant production. To calculate DIF, growers subtract night temperature from day temperature. DIF can be positive or negative and determines how growers manipulate greenhouse temperatures to control stem elongation.

Tropical Foliage Plants

• A common problem for growers during the spring season is overgrown plants, says Tina Smith with “Greenhouse Management” magazine. Growers don’t want leggy plants with sparse foliage but aim for shorter, stockier plants with lush foliage. Many potted foliage plants, such as coleus, aglaonema and dieffenbachia, are industry staples that benefit from DIF techniques. If growers start these plants too early, fertilize too heavily or provide insufficient lighting, stems elongate rapidly and plants overgrow their market deadlines. Basil has a very strong response rate to DIF and develops without hyper-elongated stems when growers lower greenhouse temperature 30 minutes before dawn and keep temperatures lowered for two hours before resuming pre-set greenhouse temperatures.

Poinsettias

• In the July 2002 issue of "Greenhouse Product News" magazine, excessive plant stretch is identified as one of the top problems of poinsettias in production. Traditionally, horticulturists have used chemical growth regulators to reduce excessive stem elongation. Poinsettias, however, are especially susceptible to chemical injury from growth regulators; they suffer stunted leaf growth and smaller bract development after improper chemical applications. North Carolina State University charts poinsettias as having “strong response” to DIF technique. As a foliage plant grown for colorful bracts, poinsettias benefit from DIF technique as an alternative to chemicals.

Trees

• In tree-liner production, keeping the trunk straight is extremely important, according to researchers at Ohio State University. Liners, or whips, are small trees, usually younger than 2 years old. If they grow too quickly in early pot production, their trunks stretch inordinately and the trees become misshapen. If early spring temperatures are unseasonably warm, plant stretch is inevitable because the difference between daytime temperatures and nighttime temperatures is greater than normal. Ohio State horticulturists compensated by increasing nighttime greenhouse temperatures to close the gap between daytime and nighttime temperatures.