Bonus November Web Content

Greenhouse Sanitation and Safety

Sanitation and Safety
Keeping greenhouses clean and customers happy
by Sally Colby

        Dave Miller's grandfather built the first greenhouse at Miller Plant Farm ( in 1928 for the sole purpose of getting a head start on the growing season.

        "He grew vegetable transplants for his farm rather than seeding directly into the ground. He gained about three to four weeks on his competition," explained Miller. "Then his competition asked him to start plants for them, and that's how we got started." Miller's great-grandfather purchased the York County, Pa., farm in 1912, which qualified the operation as a centennial farm this year.

        Today, Miller's wife, Diane, their son, Dustyn, and nephew, Steve Slyder, are key players on the farm. Miller grew up on the farm and says that there was never any question that his career would involve continuing the family tradition as a grower. Today, more than 250 customers in West Virginia, New Jersey, Maryland and Pennsylvania rely on Miller for healthy transplants, which means strict attention must be paid to growing practices.

        One important disease management and pest control tool is the scout who visits the farm weekly. "The advantage is that she visits many other greenhouses and knows what's out there, where I don't have time to do that," said Miller. "What she does is something that the typical grower doesn't take the time to do properly. She's an entomologist, but is familiar with plant diseases and can send tissue samples for testing."

        Another critical aspect of Miller's sanitation program is allowing greenhouses to rest between crops. "In our ornamental houses, we do our best to allow at least two to three weeks where there are no plants in the greenhouse," said Miller, noting that most of his greenhouses remain empty through the winter. "A lot of insects require living tissue, so when the crop is finished, we remove all plant material, clean the floor and beds, and let the greenhouse 'cook.' The puddles dry up, so the cycle for fungus gnats is broken. For any insects that hatch late, there is nothing to feed on. That's a very effective tool," he explained.

        Greenhouse cleanliness also includes specific sanitizing procedures. After a crop cycle is complete, benches are power washed to remove excess soil, and then sanitizing begins.

        "Any pots or flats that will be reused, especially plug trays, are dipped in a sanitizing solution," said Miller, adding that their system involves submersing trays for 20 minutes. "The challenge is that once you dip a certain number of trays, you have to change the water because the soil that clings to trays inhibits the active ingredient.

        "I don't reuse trays for tomatoes and peppers; I always use new trays, new flats and new inserts because of bacterial diseases. I sell a lot of vegetable transplants to other growers, and I owe them that," he said. Miller noted that sterilized trays are used for less-sensitive crops, such as ornamentals, because bacterial diseases that affect them are species-specific. Porous materials, such as wooden flats, are more difficult to sterilize, so those are steamed.

        If Miller has a problem in a particular greenhouse, particularly with bacteria, he'll rotate out of that greenhouse for the year, and then use it for a different crop. Because of seed-borne bacterial issues with tomatoes, Miller invested in equipment to treat all tomato seeds.

        "Seed companies will chlorine-treat seed, which is fairly effective on bacterial speck and bacterial spot, but not canker, which is systemic and inside the seed coat. The only way to knock that out is to raise the temperature of the seed," he explained. Miller's science-grade equipment treats seed for 25 minutes at 122 degrees. "The secret of hot-water seed treatment is drying the seed fast," said Miller. "We can't let it remain damp after treatment, so we have a process for that too." Miller noted that heat treatment isn't 100 percent effective, and that in certain weather conditions plants may still develop bacterial canker.

        Minimizing weeds on greenhouse floors helps prevent disease, but even with a solid stone surface that inhibits weed growth, spillage from watering pots results in soil and debris on the floor. "Weeds can root in that," said Miller, "but if you clean up weeds as you go, not many of them germinate."

        At the end of July, the first of 10,000 poinsettia cuttings arrived, creating potential habitat for whiteflies and thrips. "Those plants will be out before Christmas," said Miller. "Leaf debris will be cleaned up and disease risk is greatly reduced. I don't have any other plants in these houses other than poinsettias, so whiteflies can't get to anything else."

        Prior to each growing season, Miller sends an informational letter to all of his growers and includes a fact sheet on managing bacterial diseases. He advises growers on practices such as rotation, water flow patterns and spraying techniques. "You don't want to spray from an old planting to a new planting because an air-blast sprayer will spread canker from one plant to the next," he explained. "It spreads by splashing water. We tell them that they shouldn't pick when plants are wet because hands can spread diseases. Most of it is common sense, but we don't always think of everything."

        Throughout the season, Miller shares insect and disease bulletins from Penn State with his customers. He says that the biggest mistake he sees growers make when it comes to disease is not identifying problems early. "They assume it's something, treat for it and hope they hit it," he said. "Or they use a broad-spectrum treatment that might not be necessary."

        Keeping employees safe as they work in the greenhouses is an ongoing effort at Miller Plant Farm. New employees view the worker protection safety video, and Miller keeps records on safety training. "They know what I'm bound to do as the employer," said Miller, adding that even his experienced employees are shown the video every few years. "We have a specific place for chemicals, and we're very careful with re-entry times, especially in the retail area." To minimize the risk of chemical accidents, one employee does the majority of the spraying.

        Cuts and falls are the two most common incidences at the farm, and cuts are often the result of a fall. In the retail area, Miller and his employees do their best to keep items such as hoses properly stored when not in use.

        In the new 2,500-square-foot retail center, part of which is a greenhouse, the emphasis is on customer safety. Aisles are designed so that two carts can pass safely, and all grates are high-heel safe. "Where we knew there would be benching, we used a certain kind of grate," said Miller. "All bays drain to the center, so if I'm using fertilizer, I can capture the runoff and redirect it to the fields outside. The floors were a priority-the cement is sand-finished, and there are no pockets for water to accumulate." Miller noted that metal benches in the new facility have sharp edges that are fitted with plastic bumpers to reduce the risk of cuts.

        Miller Plant Farm is poised to remain a leader in the industry with the help of family members who take pride in producing top-quality transplants. Miller sums up their business with the values his father instilled in him: "One thing my father taught me is that people are more important than money. A customer will forget what he paid for plants, but he will never forget how he was treated when he bought them. A satisfied customer is much more fulfilling than a full bank account."

The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit and join in the discussions.

Photos by Sally Colby.

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