US (MI): Spring tips for busy greenhouse growers

The advent of spring signals a very hectic time for greenhouse growers in Michigan. While some of the earliest batches of flowering crops are being shipped south, propagation rooms are still very active and production lines are operating in high gear. There are baskets to hang, pots to water and liners to trim. There are schedules to adjust, equipment to fix and empty hoops to prepare for the next crop. Combine all of that with the need to scout crops and it’s more than enough to make a person’s head spin!

by Jeremy Jubenville

Here’s what I’ve seen on my recent visits to greenhouses.

Nutrition
Great job, everyone! Most crops in most greenhouses look healthy right now. There were, however, a few common correctable conditions observed over the past couple of weeks.

Iron deficiency
The most common symptom of iron deficiency is interveinal chlorosis in the newest leaves. It has the potential to show up in any operation that uses water containing substantial amounts of calcium carbonate (high alkalinity). Here in Michigan, that means just about everyone.

High alkalinity water can raise the pH of soilless substrate over time which, in turn, reduces the availability of iron (and several other nutrients) in the root zone. Some species are more sensitive to these conditions than others and have been designated as “iron-inefficient” plants (e.g., Petunia, Calibrachoa, bacopa, Vinca and others). These are going to be your indicator species and they’ll be the first to display symptoms.

Low fertility
Another minor issue I’ve seen in several greenhouses is sub-optimal fertility levels in some crops. One of the primary symptoms is lower leaf yellowing due to nitrogen deficiency. In time, the whole plant can show symptoms, appearing light green or even yellow. I’ve seen a couple cases recently where low substrate fertility, measured as electrical conductivity (EC), in combination with high substrate pH presented some unusual symptoms due to several simultaneous micronutrient deficiencies.

Read more at MSU Extension