How To Clean A Greenhouse – Tips For Sanitizing A Greenhouse

How To Clean A Greenhouse – Tips For Sanitizing A Greenhouse

Greenhouses are fantastic tools for the home gardener but they do need to be maintained. If you’ve had issues with recurring disease or insect infestations, it’s time for a thorough greenhouse cleaning. Ideally, keeping a greenhouse clean should be an ongoing task, but as we all know, what we should do isn’t always what happens. So how do you sanitize a greenhouse? The following article contains everything you need to know about how to clean a greenhouse.

About Sanitizing a Greenhouse

Whether you are a commercial grower or a home grower, keeping the greenhouse clean is of paramount importance. Over the course of a growing season, plants aren’t the only thing that’s growing; potentially infectious microbes may be as well. Algae, too, are busy developing on moist surfaces that foster fungus gnats and shore flies.

Prevention, as they say, is the best medicine and is the case here as well. It is easier and less expensive to nip insects and diseases in the bud by keeping a greenhouse clean. The cleaning and sanitizing of the greenhouse should occur as soon as possible to eradicate over-wintering pests prior to the growing season.

How to Clean a Greenhouse

Greenhouse cleaning is a two-part process: the initial cleaning and removal of items followed up with sanitizing the greenhouse. The actual cleaning out of the greenhouse means removing weeds and other living plant material from the greenhouse. Also, remove plant debris, spilled soil, and anything else that is cluttering the greenhouse. Once you have these items moved out of the way, use a shop vacuum to suck up wayward dirt, bits of broken pottery shards, etc.

Either power wash or scrub algae, grime, and fertilizer residues. If you are using soap, be sure that it is a gentle, natural soap that leaves no residue.

In the future, to make cleaning easier, the grower might wish to install weed barrier which will not only slow down weed growth, but make the cleaning of algae and spills an easier task.

How Do I Sanitize a Greenhouse?

There are four disinfectant methods used to sanitize a greenhouse.

  • Alcohol– While 70 percent alcohol kills microbes on contact, it is volatile, so the results are short lived. It is best to use alcohol to sterilize equipment like shears or propagation knives.
  • Bleach– Bleach is the most commonly used disinfectant and the cheapest. The thing about bleach is that it loses its efficacy after two hours of dilution. Dilution is the means by which the bleach is used as a disinfectant. It is not used straight but mixed with water in the amount of one part bleach to nine parts water. Prior to disinfecting pots or flats with bleach, wash out any soil or organic matter first.
  • Hydrogen Dioxide– Hydrogen dioxide is another disinfectant that is available under brand names such as ZeroTol, OxiDate, and SaniDate. It kills many types of bacteria on contact and is good for use on benches, pots, tools, etc. Like bleach, it will lose its efficacy after a while. The solution can be tested to see if it is still potent. If not, additional hydrogen dioxide needs to be added.
  • Quaternary Ammonium Chloride Salt– Unlike hydrogen dioxide or bleach, quaternary ammonium chloride salt does not lose its effectiveness. It is suited for use on pots, flats, etc., but they should be cleansed of any planting medium or other organic material first.

Keeping a Greenhouse Clean

It’s a big job so once the greenhouse has been sanitized, turn over a new leaf and resolve to take some steps to minimize future clean up. Be sure to sanitize tools, containers, and equipment right after use.

Wash your hands prior to any contact with plants, equipment, or soils. Wash gardening gloves. Have a pair of shoes or boots that are strictly for use in the greenhouse and nowhere else. Avoid bright colored clothing, specifically yellow or blue, that attracts insects which may follow you into the greenhouse.

Keep weeds pulled both in containers and off the floor. Remove any diseased plants immediately. Keep hoses hung nozzle end up instead of draping along the ground.

How Do I Clean My Greenhouse & How Often?

Table of Contents

It’s very essential to keep your greenhouse clean because it prevents unwanted pests and diseases, as well as guarantees proper light conditions. However, it takes more than just hosing down the whole structure.

If greenhouse gardening is still new to you, you might be wondering how often you have to wash your greenhouse. In fact, you’ll also need to know how to clean your greenhouse. Note that the procedure for polycarbonate greenhouses may not entirely apply to glass greenhouses. But the good thing is, you’ll get the chance to learn all of the greenhouse cleaning basics from this article.

While it’s essential to know how to clean your greenhouse, you should also understand why it is so important.


2019 Focus on Disease Control - 2019 Focus on Disease Control: Propagation

At the start of a new growing season, growers should take steps to prevent different diseases.

Fig. 1. Botrytis produces abundant masses of gray spores on diseased and dead plant parts, appearing as a fuzzy or powdery gray mold.

A new year signals the start of a new growing season. How about propagating and producing high-quality and healthy plugs (seedlings) and rooted liners (vegetative cuttings) as a New Year’s resolution? If young plants are exposed to poor propagation conditions, disease is favored, causing trouble for both propagators and growers. Disease prevention and management during propagation pays dividends throughout production.

Propagation environments and cultural practices

Provide a sanitary and pest-free propagation environment and implement best management and cultural practices to ensure high-quality and healthy young bedding plant transplants (plugs and liners). Monitor and control the propagation environment. Keeping the relative humidity below 85 percent is a challenge, but an environment that is continuously saturated should be avoided. Good air circulation across the crop can keep the leaf surface dry, which discourages foliar pathogens. Daily light integral, and the air and root-zone temperatures are also important components of the propagation environment influencing rooting and quality. Make it a practice to quarantine and inspect all incoming plant material for evidence of insects and disease. Once the new plants are incorporated into the greenhouse, scout the young bedding plant transplants frequently so that problems can be addressed early when the odds of success are highest.

Pathogens that pose the greatest threat

Botrytis is a fungus that loves moisture, causing leaf spotting on foliage and stem blighting on cuttings and young plants during propagation. Two traits make Botrytis a threat. First, any plant can be a target for Botrytis. This pathogen is not picky! Second, Botrytis produces abundant masses of gray spores on diseased and dead plant parts, appearing as a fuzzy or powdery gray mold (Fig. 1). A cloud of gray spores may be seen when diseased plants are moved. These spores may be picked up and carried on air currents and transported to healthy plants, which then become infected. Spores can be produced on plant parts that have been discarded so keep the benches and floors picked up and the trash containers covered and out of the production area.

Black root rot is caused by the Thielaviopsis fungus and can be a problem on plugs and young plants (Fig. 2). This disease is a serious threat to pansies, petunias and vinca. Other crops including cyclamen, calibrachoa, poinsettia, primula, impatiens, snapdragon, verbena, phlox, begonia, and nicotiana may also become infected by the Thielaviopsis fungus. Leaves may turn yellow (chlorosis) and resemble a nutrient deficiency. Black root rot gets its name from the dark-colored spores of this fungus. These spores are long-lived, contaminating growing mats and containers and surviving to infect future susceptible crops. Thorough sanitation measures are necessary to eradicate this fungus from the greenhouse following a disease outbreak. Growing mats and containers associated with the diseased plants belong in the dumpster because standard sanitation measures will not suffice.

Fig. 2. Black root rot caused by the Thielaviopsis fungus can turn young transplant leaves yellow (chlorosis) and roots discolored or necrotic.

Prevention and management

Reducing the amount of moisture in the production area is the best way to keep Botrytis in check. Water at a time of day when the leaves can dry rapidly, avoid oversaturating the growing media, and keep the air circulating. When these environmental control measures are not enough, fungicides can be highly effective with several products to choose from.

Preventing black root rot is best accomplished through strict sanitation throughout the production area, placing incoming plugs in quarantine for observation, scouting for early symptoms, and using a diagnostic lab for suspect samples. This disease is frequently misdiagnosed in its earliest stage when treatment with fungicides can be helpful. Once black root rot has progressed, crop quality suffers and usually cannot be restored by fungicides. In some situations, preventive fungicides are used on the most black root rot-susceptible crops to ensure plant protection.


If young plants become diseased, implement an action plan immediately. If fungicides or biologicals are used, follow the label to maximize their benefit. Using a pest and disease diagnostics lab for diagnosis and contacting your local greenhouse extension educator or university specialist can help too. Cheers to high-quality and healthy young bedding plant transplants in 2019!

Greenhouse Barriers and Traps

You’ll never be able to keep every insect out of your greenhouse. They fly in when you open the door, they crawl through minute cracks and openings, and they can hitch a ride in on your boots, tools, or new plants. However, you can keep the vast majority of insects at bay with the use of screens placed across vents, windows, and other openings. The problem with screens is that they cut down on the amount of light that gets into the greenhouse. Ideally, you will use screens whenever the windows and vents are open and remove them to allow in maximum light when the greenhouse is closed up.

Another way to help keep insects out is to have an air lock between the outdoors and the inside of your greenhouse. If you are growing crops that are prone to particular pests, such as cabbage white caterpillars on brassicas, you can also use floating row covers placed over the plants to protect them.

Sticky traps are another way to control pests in the greenhouse. Some common traps include yellow sticky traps for whitefly, and red balls for coddling moth and fruit flies. The insects are attracted to the color of the trap and get stuck on the adhesive covering. It’s a good way to monitor and identify pests that may be lurking around your plants. Put them under the benches, close to intake vents, and near windows and doors.

Michele Warmund
University of Missouri
(573) 882-9632
[email protected]

Published: January 26, 2018

Winter is a perfect time to inspect and clean shears, loppers, and saws before pruning shrubs and trees. If blades on pruning equipment were dull and nicked or tore plant tissue after cutting when they were last used, consider sharpening them or purchasing new blades. Replacement blades for Felco brand hand shears can be purchased at a fraction of the cost of new pruners. Even if blades of pruning equipment are sharp, they may need to be thoroughly cleaned to remove soil or sap left from their last use. Use a damp cloth or paper towel or simply soak blades in warm water for a short time to loosen debris. Make sure to dry the blades after washing them. For plant sap that is hard to remove, paint thinner can be applied to pruning blades and rinsed off after its use to prevent corrosion.

Pruning tools should also be disinfected to prevent the spread of pathogens among plants. Although it is not always practical to handle disinfectants when making multiple cuts on the same tree or pruning several trees or shrubs, it will minimize plant loss. Disease organisms may not be visible on tools, but they can be spread from plant to plant during pruning. Several products are available for disinfecting pruning equipment, including alcohol, chlorine bleach, trisodium phosphate (TSP), pine oil, or other household products.

Ethanol or isopropyl alcohol are ideal for sanitizing pruning equipment because blades can simply be wiped or dipped into disinfectant without a prolonged soak. Products sold as rubbing alcohol usually contain 70% isopropyl alcohol and can be used directly from the container. Ethanol can also be used without dilution. Both types of alcohol can be purchased at drugstores or variety stores. Like other flammable products, they should be stored away from heat sources.

Unlike alcohol, chlorine bleach should be diluted to a 10% solution before disinfecting blades of equipment. To prepare a 10% solution, mix one part bleach (using any brand available) to nine parts of water. When preparing a bleach solution, avoid inhalation of fumes, wear rubber gloves to prevent skin contact, and protect your clothing from bleaching. Use the bleach solution within two hours after it was prepared and soak blades of pruning equipment for 30 minutes. Because bleach solutions become 50% less effective as a disinfectant after two hours, make a new solution after this time. After soaking blades in bleach, rinse tools with clean water to prevent corrosion. Although chlorine bleach is inexpensive and readily-available, it is not as effective against viruses as some other disinfectants.

Household disinfectants, such as Lysol or household wipes can be used to sanitize pruning blades, but their effectiveness against plant pathogens has not been widely evaluated. While most household products are commonly available and are not generally corrosive, they are relatively expensive compared with other disinfectants.

Pine oil is available as a multi-purpose household cleaner at some retail outlets. Blades of pruning tools can be soaked in a 25% solution (one part pine oil to three parts water). While not as corrosive as chlorine bleach or TSP products, pine oil is also not as effective as bleach for disinfecting pruning equipment. Pine-Sol products currently sold in stores do not contain pine oil and their usefulness as a disinfectant for pruning tools is unknown.

Products containing TSP are relatively inexpensive when purchased at hardware, home-improvement, or other retail stores, but are corrosive to pruning blades. Products containing TSP are often sold as all purpose or heavy-duty cleaners for decks, siding, or for surfaces in preparation for painting. Like chlorine bleach, TSP products should be diluted to a 10% solution, using gloves to prevent skin contact with undiluted granular material. To disinfect blades of pruning shears, soak them in the 10% solution for at least three minutes before rinsing with water and drying them. While TSP products may be useful before pruning, the time required for soaking limits their usefulness during pruning.

Several multipurpose disinfectant products can be purchased from horticultural suppliers for greenhouse and field use. Some of these products, including Physan, Kleengrow, GreenClean, Greenshield, and MicroBLOC are labeled specifically for ornamental crops, non-food surfaces, packing lines (SaniDate), or cutting tools (ZeroTol). Some products require a ten minute waiting period after application, but do not require rinsing afterwards. Carefully read and follow label precautions when using these disinfectants.

Regardless of the disinfectant used, sanitizing tools during pruning is beneficial to minimize the spread of hard to control disease organisms that have few pesticides available for their control. Since there are many disinfectants available, chose the product that is most practical for your situation.

Watch the video: How to clean your greenhouse