Keep it clean

When I managed a commercial greenhouse we did our major greenhouse cleaning the week leading up to Christmas. We would remove all of the benches and wash them top to bottom and take up the floor covering and pull any weeds that had accumulated between the nooks and crannies. It was a good time to do the cleaning because it was a period of time when production had stopped and just a few weeks before it would start again for the spring season.

Of course, you don’t want to wait until Christmas to clean and sanitize the greenhouse. Day to day preventive sanitation is necessary to hold back the constant threat of disease pathogens and insects. If you establish a routine or protocol for good sanitation you will improve your bottom line with fewer lost plants and a more efficient, productive greenhouse, according to Nathan M. Kleczewski, extension specialist in Plant Pathology at the University of Delaware.

“Poor sanitation causes most disease problems I see in the greenhouse,” says Daniel S. Egel, extension plant pathologist at Southwest Purdue Agriculture Center. “The problems include damping off of seedlings due to contaminated soilless mix, bringing in disease and insect problems on shoes and tools, and the overwintering of disease problems from last year’s crop that wasn’t properly cleaned up.”

Fortunately, it isn’t difficult to maintain a clean house, but it does require due diligence and a trained eye. The first thing to do is to “think clean” according to Egel and Kleczewski, co-authors of Sanitation for Disease and Pest Management, a publication of the Purdue University Extension.

There are several measures you can take to prevent disease and insect infestation, including perhaps a few you hadn’t thought about.

Keeping Benches Clean
Greenhouse benches are like the counter tops in the kitchen. They need to be kept sanitized to prevent plant contamination. Chlorine bleach, mixed to a 10 percent solution and allowed to stand for five minutes is very effective at killing disease pathogens, note the authors of the above paper. Caution is in order when using bleach, which is highly volatile, phytotoxic, and can irritate mucus membranes and lungs, and can even corrode metal.

Another product that can be used in greenhouses to sanitize are those products containing quaternary ammonium, which are less volatile and more stable than bleach but don’t penetrate wood so well, so use this product mostly on metal benches.

Products containing chlorine dioxide effectively sanitizes surfaces. Chlorine dioxide is a gas, so it can penetrate and infiltrate greenhouse nooks and crannies far better than liquid products. Always follow the labeling on a product and wear the proper protective gear.

Check beneath your feet
The floor is a big source of disease pathogens and insects. If you use a landscape fabric underneath your tables beware the critters have a place to hide and multiply. Greenhouse pathogens can survive a long time in the soil. Cement and gravel floors are less problematic when it comes to harboring insects and disease, notes Kleczewski. If you are using a landscape fabric it can be cleaned with a bleach solution but ultimately should be replaced often, which we did about every third year in the greenhouse I managed.

Bringing in plants
One lesson we learned the hard way in our greenhouse operation, which focused mostly on bedding plants and poinsettias, is not to bring plants into the greenhouse, or at least not until they are properly quarantined and checked for insects and disease. Carefully inspect plugs you’ve ordered, or any other plants you’re bringing inside for signs of disease or insects, which unfortunately may not be evident on the plants when in the initial stages of their development.

Keeping tools and equipment clean
In the rush of deadlines and the sure volume of work required to produce a good, clean crop of bedding plants or any other greenhouse crop, it can be easy to overlook keeping the tools of the trade clean.

“Growers who use soilless mixes spend a lot of money when purchasing bags of mix. However, they often use unsterilized tools in the mix, pour the mix on unclean surfaces, or use pots or trays that are contaminated from last year,” says Egel.

It is particularly important to disinfect tools after taking plant cuttings. Viruses and bacteria are easily spread between plants. A 70 percent ethanol solution is very effective for tool sanitation, say Egel and Kleczewski.

Another thing that perhaps goes along with keeping equipment clean is disinfecting any used equipment you’ve acquired, including purchased greenhouses.

Kleczewski says growers buy used houses and sometimes don’t disinfect the various components, which can set the stage for problems like mold and powdery mildew.

Establish a culture for clean
The most efficient and productive greenhouse operations have a protocol they follow for keeping the greenhouse as spiffy as possible. Part of this protocol, besides keeping tools and equipment clean is to disinfect benches after each crop, disinfecting pots before reuse, and in some cases requiring visitors to put on protective clothing before entering the house. For some operations, like Four Star Greenhouse, headquartered in Carleton, Mich., greenhouse sanitation is just part of their culture.

“It (sanitation) is something that is inherent in the culture here,” says Dan Foster, site manager for Four Star Greenhouse. New hires simply learn from team members how to run a clean greenhouse.

Part of that culture or regimen at Four Star includes daily cleaning of the concrete floors with a Zamboni machine, thorough cleaning of benches after finishing each crop, and annual cleanings where everything gets washed down with chlorine bleach administered through a power washer. In addition, Foster says they never let trash or weeds accumulate in the greenhouse, two things he says can be detrimental to a greenhouse.

One thing Foster says they’ve given up on is foot mats that are recommended to clean pathogens off your shoes before you enter a greenhouse.

Foster says they ran cultures from the mats and found that these mats accumulate a lot of harmful disease pathogens that can spread throughout the greenhouse. Like Kleczewski says, greenhouse sanitation isn’t rocket science. It’s more of a culture that develops over time from practicing good sanitation in the greenhouse.

For more: Daniel S. Egel, Southwest Purdue Agriculture Center; egel@purdue.edu.