How To Prevent Mold In Your Greenhouse (Keep It Clean)

If you have a greenhouse, you may be wondering how to prevent the growth of mold or mildew during hot and humid weather.

So, how do you prevent mold in your greenhouse?  One way to prevent mold in your greenhouse is to control moisture levels by watering plants carefully and allowing for air circulation.  Another way to prevent mold in your greenhouse is to clean thoroughly between growing seasons.

Of course, there are some ways to get rid of mold in your greenhouse if it has already made an appearance.  Before we get to that, let’s get into how to prevent mold in your greenhouse so that you can avoid the problem in the future.

How to Prevent Mold in Your Greenhouse

To prevent mold in your greenhouse, it all comes down to water, air, and cleaning.  If you get these three basics right, then your greenhouse has a much better chance to stay mold-free.

To prevent mold in your greenhouse, control moisture and air circulation, and clean thoroughly.

Mold is a fungus that grows best in warm temperatures.  Mold also requires high humidity (above 85%) in order to thrive.  Standing water is another factor that can help mold to grow.

If we can control the water and air circulation, then we can prevent mold in most cases.

Carefully Control Water and Air Circulation in Your Greenhouse

The leaves of your plants are one potential breeding ground for mold, so it is important to water them properly and keep the foliage dry, if possible.

Keep Your Plant Leaves Dry

Wet plant leaves give mold the perfect place to grow.  After mold is established on a plant, it can easily spread to nearby plants, causing an all-out mold infestation.

One of the most important steps in preventing mold growth in your greenhouse is to keep plant leaves dry.  This sounds easy, but there are a few things to keep in mind.

rain splashing on plant
Keep your plant’s leaves dry – wet leaves invite mold growth.

First, avoid misting your plants with a hose attachment, watering from overhead, or using foliar sprays.  All of these will wet the foliage and invite the growth of mold.

Instead, water your plants close to the soil, to avoid getting the leaves wet.  Consider side-dressing the plants with any nutrients they may need by working it into nearby soil and watering it in.

Also, be careful of where you put your plants.  Avoid putting them underneath places where condensation drips down from the plastic or glass ceiling of the greenhouse.  Otherwise, the leaves will get wet, which will lead to mold growth as described above.

Finally, water your plants in the early morning, not at night.  Watering in the morning, when the air is cooler, gives the water time to soak into the soil and get to the roots of plants.

If you water later in the day, the heat and sun will cause more of the water to evaporate.  This leads to high humidity levels in the greenhouse, which invites mold growth.

Avoid Over Watering Your Plants

Over watering your plants is another mistake that will cause mold growth in a greenhouse.  When plants are over watered, the soil contains more moisture than the plants can use.

garden hose
Do not over water your plants, or the soil will stay too wet and become a place for mold to grow.

If the soil stays too wet for too long, mold can grow directly on the surface of the soil.  It can then spread to plants or over the soil to colonize the entire greenhouse.

To avoid this problem, water your plants deeply, but less often.  This will give the soil a chance to dry out between waterings, which will prevent mold growth.

Always check the soil moisture before watering – if it already feels moist, then there is no need to add more water.  In fact, you can “kill your plants with kindness” by over watering.

For more information, check out my article on over watering your plants.

Leave Enough Space between Plants

In addition to controlling moisture levels in your greenhouse, it is also important to allow for proper air flow.  One way to do this is to leave enough space between plants.

First of all, this allows air to flow more freely between plants.  This allows any water on the plants or in the soil to evaporate, instead of staying put and providing a place for mold to grow.

Also, leaving space between plants prevents mold from spreading quickly if you do have an outbreak in the greenhouse.

Allow Ventilation in Your Greenhouse

Leaving enough space between your plants is only half the battle.  To allow fresh air to replace stale air in the greenhouse, you will need to open vents or doors on the greenhouse.

greenhouse vents
If your greenhouse has vents, open them up to let some air in.

You can also use fans to circulate air and dehumidifiers to dry out the air in your greenhouse.  Also, remember to keep these machines clean to avoid blowing mold spores around.

Keep Your Greenhouse Clean

Maintaining proper moisture levels and air circulation in your greenhouse is important for preventing mold.  Once you have done this, it is time to come up with a plan for keeping the greenhouse clean, including tools of the trade (pots and containers) and the structure itself (glass, plastic, wood, or metal surfaces).

Sterilize Pots, Containers, and Tools

To keep mold at bay, you should have a regular cleaning schedule for any tools you use in the greenhouse.

Even if you don’t see any mold growing, it is important to clean to get rid of any mold spores that are waiting for the right time to start a new colony. Start by sterilizing your pots and containers.

clay pots
Sterilize your pots and containers to avoid spreading mold from one year to the next.

First, empty out the soil and plant matter from the pots.  You can add the soil and plant matter to your compost pile and reuse it next year.

Next, rinse off the soil from the pots, and use a rag to wash them with soap and water.  Rinse the soap off of the pots.

Then, soak the pots in a solution of water and vinegar (3 parts water, 1 part vinegar) to kill any mold.

Finally, rinse the pots off with clean water and let them dry.  Store them in a clean, dry place for next year.

You may also want to sterilize your gardening tools, such as pruning shears, on a regular basis.  To sterilize your tools, use a clean rag and some rubbing alcohol to wipe them down and kill any pathogens.

This will prevent the spread of diseases between plants, and a healthy plant is more likely to resist mold growth.

Clean Surfaces between Seasons

In addition to cleaning the tools and containers in your greenhouse, it is important to clean any surfaces that may harbor mold growth.  This includes:

  • the top and all sides of metal containers
  • the top and all sides of wooden benches
  • plastic or glass panels used for the tops and sides of the greenhouse structure itself

To clean the surfaces in your greenhouse:

  • First, remove any debris from the surface, including dirt or dead plant matter.
  • Next, wipe away any remaining dirt or dust with a wet rag.
  • Then, use a vinegar solution (1 part vinegar to 3 parts water) to wipe down the surfaces.  You may want to wear gloves for this step, since vinegar can be nasty on your hands if they are exposed for too long.
  • Finally, wipe the surfaces with a dry rag to get rid of any excess water and vinegar.

Just like you schedule a time to start seeds and transplant seedlings, you should schedule a time to clean your greenhouse and keep it mold-free.

How to Get Rid Of Mold in a Greenhouse

We’ve talked about how to prevent mold in a greenhouse.  Now let’s talk about how to get rid of mold when it is already in your greenhouse.

Note: some people are allergic to mold, so wear a mask, safety goggles, and gloves when taking the steps below.  That way, you can avoid breathing in mold or getting it into your eyes or on your hands.

After finishing your work, you may want to wash the clothes you were wearing to avoid breathing in any mold later.

Remove Infected Plants and Soil

First, remove any plants that are infected with mold.  Mold growth on plants will vary in color (commonly, you will see mold that is white, gray, or black).

sooty mold
This plant has sooty mold on it, which is caused by the honeydew (waste) left behind by aphids after they feed on a plant.

You can compost these plants, but to prevent the mold from growing or spreading (due to spores on the wind), you can bury the plants instead.

Next, remove any soil that shows signs of mold (usually, a white or gray fuzz on the surface of the soil), and either compost it or bury it elsewhere.

Use Vinegar to Clean Surfaces

Vinegar will help to prevent mold growth, but it can also help to remove mold once it has already started to grow on surfaces.

spray bottle head
Fill a spray bottle with a vinegar and water solution and use it to cover any surfaces with mold on them.

First, fill a spray bottle with a vinegar solution (1 part vinegar to 3 parts water) and spray it on the surface with mold on it.

Wait a bit and let the vinegar work on the mold for a while.

Then, use a rag to wipe off the mold from the surface.  You may want to use multiple rags to avoid spreading mold around when wiping the surfaces.  Otherwise, wring out the rag into a bucket of water every so often.

For more information, check out this article on cleaning and disinfecting a greenhouse from the University of Massachusetts at Amherst Extension.


Now you have a much better idea of how to prevent mold in your greenhouse.  You also know what to do if mold has already started to grow in your greenhouse.  Remember: it’s all about controlling water levels, allowing air circulation, and cleaning thoroughly.

You might also be interested in reading my article on how to deal with mold on wood mulch.

I hope you found this article helpful – if so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!


Jon M

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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