A greenhouse is a great investment for growers who want to enjoy year-round gardening, but like any other worthwhile investment, it must be properly cared for in order to maintain proper function, which is why routine greenhouse maintenance is so important. While you need to keep up a basic cleaning schedule and keep an eye out for damage to the greenhouse structure all year long, a more in-depth cleaning should be carried out once a year.
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Greenhouse growers who keep plants throughout the winter may want to do this process in the spring so they can safely remove plants to the outdoors without fear of frost or heat damage. Those who refrain from growing during the winter months should instead work during the late fall or winter so the greenhouse can stay dormant long enough for all pathogens to die off before new plants are introduced in the spring.
Basic Greenhouse Maintenance
To prevent the spread of disease or pests from one crop to another, keep crops separate from one another and don't overcrowd plants. Clean up spilled soil and water immediately so they do not develop pathogens. Remove weeds and algae growth as soon as you notice them since these can both spread disease.
Always remove plants affected by disease or pests as soon as you notice. Depending on the problem, it might be treated, or the plant may need to be destroyed, but even if it is treatable, the plant should be quarantined away from healthy plants until it is healthy as well. Be sure to wash reusable pots, gardening tools and accessories after use to reduce the spread of pathogens.
Deep Clean Your Greenhouse
While routine greenhouse maintenance is important, it's critical to do a deep cleaning once a year as well. This is a great chance to check the structure and your equipment for problems and also to help eliminate any pests and diseases. Look for a disinfectant that can effectively kill plant pathogens, such as Strip-It, Biocide 100, SaniDate or oxygen bleach, and always follow manufacturer recommendations regarding the proper dilution of these products.
For deep cleaning, you'll need to remove everything from the greenhouse. This not only means taking out the plants but also removing benches, tools, pots and more — essentially everything not screwed or nailed down.
Before taking everything out of the greenhouse, take a moment to inspect your equipment. Testing your ventilation system, irrigation system, heating system, propagation trays, tools, etc. is one of the most important parts of your yearly greenhouse maintenance, as it not only helps to ensure your greenhouse will function properly but also reduces the risks of potentially dangerous and expensive problems, like fires and floods. Check the cords, tubes, lights and plugs for damage aside from just checking their functionality. Be sure to label or set aside anything that has a problem so you can repair or replace it later.
After inspecting your equipment, be sure to unplug all electrical accessories, such as fans and heaters, even if you can't remove them from the structure. If you are still keeping any living plants in the greenhouse, keep an eye on the weather forecast to make sure the weather will remain favorable for at least a few days so your plants won't get damaged while you clean.
Examine Your Plants
When removing your plants, examine them for pests or disease. Set any infested or infected plants away from the healthy plants and then take time to identify the problem. Some issues, like whiteflies or spider mites, can be treated, and these plants should be placed in quarantine away from the others until they are healthy again. Others, like those infected by fusarium wilt, will need to be destroyed entirely. For these plants, make sure you do not compost them or the pathogen may then contaminate the compost.
Clean the Greenhouse Structure Itself
Start by cleaning and inspecting the outside of the greenhouse structure, working from the top down. This way, the water will drain down to the floor as you go, and if there are any leaks on the inside, they will flow to the inside. Use a long-handled mop to clean the roof, taking care not to place any weight on the top of the structure. If you have gutters, be sure to remove any leaves and other debris before moving down to clean the glass and frame below. Once you've cleaned the outside, move to the inside, again working from the roof down to the floor.
Remove any visible dirt and debris before cleaning the rest of the surfaces because these can reduce the effectiveness of disinfectants and may even already be infected with pathogens. Next, scrub the frame and any solid walls with a disinfectant. Only then should you work on the glazing. Be sure to get in the crevices around glazing, screens, fans and vents, as this is where you are most likely to find dirt and mildew buildup.
Rather than just cleaning the surface, remember to spend a little extra time scrubbing porous surfaces, such as brick or wooden frames, so the disinfectant has a chance to sink into the material. Be sure to fully scrub away any moss or algae growing on your greenhouse materials, including in the vents, as these can prevent proper airflow and can make your greenhouse growing efforts more difficult. If your frame is wood, take time after you've finished scrubbing and use a brush to apply a vegetable-based horticultural oil, such as neem oil, to any exposed wood, which can suffocate pests hiding in the crevices.
For windows or rigid plastic, use a squeegee and a disinfectant. For greenhouses with plastic sheeting, use a soft cloth or sponge and a mild detergent, such as dish soap mixed with water.
Inspect Your Structure and Equipment
While you clean, keep an eye out for any cracks in the frame, loose glazing or screens and uneven or poorly fitting doors, windows or screens. When you get to the floor, look along the foundation to ensure there are no gaps large enough for small animals to get into the structure. If you have brick walls, check the mortar for cracks. Pay special attention to the condition of wood that has moss growth, as this can sometimes be a warning sign of rotting caused by excessive wetness.
When cleaning aluminum frames, which you likely have if you purchased a greenhouse kit, look for bends in the frame, check the reinforcement plates for movement and keep an eye out for white blooms. While aluminum doesn't rust, these white blooms are a similar type of corrosion. Fortunately, you can prevent further corrosion by painting, and in most cases, this should be enough to avoid serious problems.
Clean the Floor
This is an important part of greenhouse maintenance all year, but it's particularly important when you have all benches and other things that normally sit on the floor completely out of the room. How you clean will vary based on your actual structure. For concrete floors, you should use soap with disinfectant to scrub the concrete and remove any dirt, debris and algae, paying extra attention to corners, cracks and areas normally under benches. Be sure to remove any weeds growing in cracks or corners.
For dirt and gravel floors, it's a good idea to remove your weed-barrier mats and set aside any damaged ones that will need to be replaced. Obviously, for gravel floors, you'll need to remove the gravel first, so you may choose to avoid this step if you do not notice any weeds.
With both dirt and gravel, you may not be able to scrub the floor, and you'll likely have some weeds that need to be pulled that may have algae. To remove algae growth, wipe off the algae as much as possible with a wet paper towel and then apply a thin layer of cinnamon to the floor, which is a natural algae inhibitor. Also sprinkle some diatomaceous earth along the floor to kill off any insects that enter your greenhouse.
Upon completion, lay out your weed-barrier mats again. If you do not already have some, it may be worth investing in these, as they not only prevent weeds but also help reduce algae growth.
Clean Your Surfaces, Equipment and Accessories
First, remove dirt buildup on all surfaces, tools, pots and accessories and then clean them with a disinfectant diluted with water. Thoroughly rinse with water after cleaning to ensure the disinfectant will not later interfere with plant growth. For raised beds, remove all soil, clean the surface as well as possible with water and a mild detergent, remove as much soap as possible and wait until you are ready to plant again before adding a fresh, new layer of clean soil. Recycle or dispose of any used disposable seed trays and pots, and if you have had any disease or pest infestations, you may even want to dispose of the unused ones.
Take special care to clean your irrigation system, as these are prone to dirt clogs, gnat infestations and buildup known as "biofilm." Mix disinfectant with hot water and then use this solution to flush out your lines, to soak your dipper heads and to scrub out any holding tanks and/or fertilizer reservoirs. Be sure to look for any cracks, clogs or leaks in the system while you work.
Greenhouse Maintenance for Soil
Old soil can be loaded with problematic pathogens, like fusarium wilt, grubs, root aphids, pythium and more. That doesn't mean you need to throw it out, but it does mean that old soil should be rejuvenated. Simply put it in a compost bin for a year, and it should be healthy and fertile again. In the meantime, start using new, disease-free soil that has already been composted for a year or that was purchased at a garden-supply store.
Make Any Necessary Repairs
Now that you know what's broken or showing signs of wear, you can take efforts to repair it. Bent or otherwise-damaged wood or aluminum will need to be repaired or replaced, and the best time to do this is when you notice the damage so it does not cause other problems in the greenhouse structure.
If your wood or brick has been penetrated by algae, paint or sealant may help. Paint may also be the solution to prevent further corrosion on an aluminum frame. Repainting, staining and mortar repair should all be done in dry, reasonably warm weather, so if it's too cold or wet outside when you are doing your deep clean, you might need to remove your plants again in a few months to handle these greenhouse maintenance tasks.
Repair any cracks in concrete with caulk or other repair material. For dips in a soil floor, level out any dips in the ground where standing water may pool by adding and compacting more dirt into the dips.
If you notice that the door or windows are allowing in cool breezes, figure out if it is coming from around the door or window or from around the frames. If it's coming from around the door or window, add weather stripping. If it's coming from around the frames, apply caulk as needed.
Also, repair or replace any damaged or broken equipment as necessary.
Fix Greenhouse Glazing
If you have an issue with your glazing, it should be repaired as soon as possible. Loose glazing clips should be put back in place and can be secured with silicone sealant to provide extra strength against the strongest of winds.
You'll want to replace broken or cracked polycarbonate or glass as soon as possible, but you can temporarily prevent wind chill from damaging your plants by replacing a broken pane with a piece of cardboard covered in plastic sheeting or by taping cracks with glazing tape. Glazing companies generally have most standard sizes of horticultural glass and polycarbonate in stock, but if yours is not standard, you may have to special-order it.
Rips in plastic sheeting are more easily repaired since they can be taped together with glazing tape placed on the inside and the outside of the rip. Particularly large holes in the sheeting can be fixed by taping a square of polyethylene over the hole and taping on each side with glazing tape.
The Natural Sterilization Process
If the weather permits you to leave your plants outside for a whole week during the summer or if you're between crops, you can sterilize the inside of the greenhouse naturally by sealing off all vents, windows, doors and other openings and letting the temperature rise over the course of a week. This should allow the temperature to get high enough to kill off pathogens, which can be particularly beneficial if you had any recent pests or diseases wreak havoc on your plants.
- University of Massachusets Amherst: Cleaning and Disinfecting the Greenhouse
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- GrowVeg: How to Windproof Your Greenhouse
- Click and Grow: You Accidentally Grew Algae, Now What?
- Hartley Botanic: 5 Top Tips for Greenhouse Maintenance by Ewan Michaels
- Rural Living Gardening: How Does A Greenhouse Work? Tips For Greenhouse Maintenance
- Gothic Arch Greenhouses: Summer Greenhouse Maintenance Checklist
- University of Florida IFAS Extension: Greenhouse Heating Checklist
- Eartheasy: Greenhouse Cleaning and Maintenance for Beginners