Michigan State Webinar Tackles Tips for Holding Plants

Slide content by Dr. Eric Runkle and Dr. Roberto Lopez, Michigan State University.

One of greenhouse growers’ biggest COVID-19-related issues is a lack of plant demand from the retail side, which in turn leaves head growers and their production teams down the winding road of how to handle plants stuck in failure-to-launch mode for a couple extra weeks.

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This was the subject of a recent webinar hosted by the Department of Horticulture at Michigan State University (MSU). “Tips to Hold Greenhouse Crops,” featured the work of MSU researchers Dr. Roberto Lopez and Dr. Erik Runkle.

Runkle addressed the topic from a greenhouse floriculture perspective, while Lopez took the angle of doing the same in hoop houses to outdoor transplants, with some greenhouse data thrown in as well. Both presented some interesting research results during the presentation.

“Plants are not shipping when anticipated, and some people are not able to sell their crops right now,” Runkle said to kick off his presentation, alluding to the sudden uncertainty that COVID-19 has thrust upon the market.

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Runkle then ran through his top strategies for growers along those very lines:

  • Increase plant spacing: By widening plant spacing, growers increase the ratio of red (R) to far-red (FR) light spectrum.
    “A higher R:FR means less stretch on those plants,” Runkle shared.
  • Lower the temperature in the greenhouse: Seems like a no-brainer, but Runkle says “sometimes the only way to slow down crops without terminating them” is to lower the greenhouse temperature. More specifically, each floriculture plant has a different base temperature versus optimum temperature window inside of a greenhouse. Knowing that metric for each cultivar and being able to keep the plants relatively close to the base temperature (without stressing them too much) is a key skill to develop. Find that balance, he advises.
  • Airflow still crucial: Precisely, horizontal air flow (HAF), according to Runkle.
    “Air mixing is sometimes necessary to improve the uniformity of temperature, humidity, and carbon dioxide,” he said, noting that a deficit in this area can lead to non-uniform growth and development, and during the winter months it becomes even more crucial.
  • Plant Growth Regulator Applications: Not many of these can be used by greenhouse vegetable, cannabis, or hemp farmers, but floriculture growers have access to these tools to unlock extra holding capacity in plants when necessary. Runkle says two active ingredients are especially noteworthy for the 2020 growing season: Paclobutrazol and Ethephon.
  • “Paclobutrazol seems to be the first choice for most growers because it stays in the soil and plant for very long,” Runkle explained. “And with Ethephon, the response will be variable and less predictable, but it’s a decent option to delay flowering a crop you have to wait to ship out.” From listening to Runkle’s talk, it sounds like the latter is also a little more complicated agronomically to apply than Paclobutrazol.

Runkle covered a few more topics, including strategies around pinching and trimming to limit branching growth, using controlled release fertilizers instead of straight rate — a strategy he called “fertilizer restrictions” — and all other sorts of topics during the Q&A session at the end of the webinar.

Lopez’ research on holding cold-tolerant crops with little to no heat — such as one would experience in a bare bones hoop house or temporary structure — was really interesting as well, as he included greenhouse data in that section of the presentation to show the differences between greenhouse, high tunnel, and field production.

“Plants were obviously delayed when grown outdoors but were of higher quality compared to greenhouse grown as well as those grown in a high tunnel,” Lopez said, summarizing his research conclusions.

But, if you’ve got the time, why take my word for it? Head over to MSU’s website for an archived recording.

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