A look inside the Grower Workshop

CropKing hosts its two-day Introductory Grower Workshop for current and future greenhouse produce growers in Lodi, Ohio. The workshop features classroom lectures, as well as some hands-on work in the greenhouse.

Here are some takeaways Produce Grower gathered from a visit to a recent Grower Workshop.

Selecting the right crop

When opening a produce greenhouse or adding onto an existing one, an important decision each grower will have to make is what they want to grow. Paul Brentlinger, president of CropKing, said it is crucial that growers consider what is profitable versus what is possible. While nearly any crop will grow in a hydroponic system with the right care, some crops might not yield enough fruit or vegetation, or yield enough in a certain period, to be financially sound.

Market demand should largely determine what type or types of crop a grower chooses to produce, said CropKing horticulturist Matthew Kispert. Just because a grower has mastered how to produce something doesn’t mean customers require or want that crop.

For beginning growers, such as many of those who attend the workshops, CropKing has narrowed its crop recommendations into two main groups: lettuce and leafy greens crops grown in nutrient film technique (NFT) systems and vining crops grown in bato bucket systems. For more information about lettuce and leafy greens crops, click here For more information about vining crops, click here

Measuring and adjusting alkalinity and electrical conductivity

Because hydroponic growers use water to produce their crops, the quality of their water is important, said Jim Brown, horticulturist at CropKing. For its Grower Workshops, CropKing encourages growers to bring their greenhouses’ source water. While in class, growers measure the electrical conductivity (EC) and pH of their source water.

The target pH of water for hydroponic use is a pH of 5.5 to 5.8 and can be measured using a pH meter. Most source water, Brown said, starts at a high pH, so growers will often need to add acid to the water to bring it into the desirable range. Depending on the alkalinity, or the buffer, of the water, the pH will decrease at a certain rate as the grower adds more acid.

In the Grower Workshops, growers use an eyedropper to add diluted battery-strength sulfuric acid to their source water to adjust the water’s alkalinity and get it to the desired pH range. They count the number of drops that it takes to enter that range, as well as the number of drops until the pH begins to drop at a faster rate and lose its buffer. By creating this titration curve, they learn their water’s alkalinity.

Monitoring and controlling pest and disease issues

When managing pests and diseases in a hydroponic greenhouse, CropKing prefers to take a preventative rather than curative approach. Growers should be educated about a given issue and prepared to deal with it. CropKing recommends using biological controls and other non-conventional products, due to restricted chemical use in greenhouses, as well as the possibility of resistance development.

The most common pests in hydroponic produce greenhouses are aphids, thrips, whiteflies, fungus gnats, spider mites and russet mites, Kispert said. Aphids produce both sexually and asexually, and at a rapid rate. Because of this, it is best to catch aphids early. The first colony that arrives in the greenhouse will often be in a concentrated area, so growers need to regularly and thoroughly check leaves, including their undersides.

Thrips, by comparison, are extremely small. While smaller generations of thrips can fit through insect netting, adult thrips cannot, so growers should use netting, Kispert said. They should also scout by hanging sticky cards, which track pest population densities, and have a jeweler’s loupe on-hand to identify the pest up-close. For control of thrips, growers can release predatory mites.

Meanwhile, common disease issues in hydroponic produce greenhouses include powdery mildew, downy mildew, Botrytis, Pythium, as well as some instances of viruses, and more rarely, early and late blight. “Powdery mildew spreads when it's really dry, and it sticks to the leaves when it's really humid,” Kispert said.

Downy mildew, by contrast, is often a storage issue, arising in a cooler or on a shelf in a dark area. Botrytis infects crops, usually tomatoes, through open wounds and open water, and can be best avoided by performing leaf removal in the morning — before temperatures begin to drop — and trimming leaves in the canopy to improve airflow.