6 Tips for Cleaning Your Greenhouse Before Winter Sets In

The inside of Donna's Greenhouse

Its never too early to get a head start

My husband and I planned a mid-week ski trip but on departure day I was still in my off finishing a time-sensitive project. We were staying overnight at the hill, it was still a workday, and the car was loaded up. There was no rush to get moving.

My other half was off work for the day. His bags were packed and he kept checking in asking if I was ready to head out.  I finally asked him to help us get ready by cleaning out the refrigerator.

I am not sure if he had any previous experience with this task or if it is just the way I worded the request, but he got right on it. Except he didn't clean out the fridge, he cleaned it: a much more intensive job that took hours.

"Cleaning out" - in my vernacular - means tossing the old food and pouring out the milk. "Cleaning", means scrubbing down all the surfaces. It is a much more intensive task.

At this time of year, it is fine to "clean out" your greenhouse. But if you have time, cleaning is a good idea as well. Get rid of dead or dying plants, weeds and other stuff that will rot, meltdown or cause problems going forward. If you have time, sweep the floor and wipe down dusty, spore-filled surfaces, empty pots and do a bit more than just tidying up.

Keeping the greenhouse clean- or, at the very least, tidy - helps deter so many future problems. That's why in mid-November I am cleaning out and cleaning my greenhouse.

When to start cleaning?

The best time to clean the greenhouse is when you have the fewest plants growing. This is why true spring cleaning doesn't work for greenhouse gardeners. Spring is that special time of year when we have shelves spilling with potted tomatoes, beds packed to capacity with winter crops, baskets hanging from the roof and extra pots of geraniums spilling out into the paths and beds. Spring is the opposite of empty. I find November is the perfect time to bring out the cleaning supplies.

Donna Balzer cleaning the inside of her greenhouse

Donna Balzer cleaning the inside of her greenhouse


Here are six tips for cleaning your greenhouse this month:

Clean on a sunny, warm day

After a big snowstorm in Calgary in October, early November brought highs of 23 C (73 F). At the same time in Toronto, after heavy early season frost, they had temperatures in the 20's C (High 60s/Low 70s F). In other words, you never know when you are going to get a sunny day so jump on it and dedicate time to your greenhouse. It will be good for your positive vibes to get into the warm greenhouse sun and it will be good for the garden too.

Cut back on watering

A sunny day makes you think of spring and you imagine plants growing as the sun shines brightly. But it will be getting cooler, cloudy and maybe even snowy again soon. Sitting water is never a good thing so I stop watering in fall. Extra moisture and cold soil encourage insects like fungus gnats to multiply.

If the soil is moist in fall going into winter, there is no need to water for a while. Days are so short and temperatures are cool so the demand for water from your plants goes down. I shut off the water and disconnect the hoses at this time of year to stop drips and accidental floods. Winter crops are in "holding" mode because they are not growing vigorously. Your greenhouse becomes a fridge for the cool season plants. A little hand-watering, if needed, can always come later. Today, it's time to shut off.

Remove cobwebs

While spiders are largely good for your garden, they sometimes offer a runway to the creepy little critters that are distantly related - the spider mites. Luckily spider mites will go dormant this month, but their hideouts can be the cracks and crannies so they are worth cleaning. Using a duster, remove the visible webbing and insects you see in your corners and ledges. Wipe surfaces with a damp cloth and a gran a bucket of soapy water.


Remove extra plants

Yes, there are still a few flowers and fruit on tomatoes, but with diminishing light, there will be fewer and fewer fruit for you to harvest. If you are not planning on heating your greenhouse, warm climate plants will quickly perish. They will start to mold and spread spores. It is time to turn the greenhouse over to cold season plants. Mustard greens, spinach, arugula, watermelon radish and root crops like carrots or beets will withstand frost levels.

Unless you are heating to consistent Summer temperatures, the warm season crops like melons, cucumbers, tomatoes, and peppers should be pulled now. Pick the fruit first and then pull the plants.

Wash overwintering plants

I leave lemons and lime trees in my greenhouse over winter, but I wash the leaves of these plants to remove pests or diseases first. Commonly, cool nights and warm days encourage sooty mold to grow in the honeydew of scale insects. First, I remove the scale adults with a Q-tip dipped in alcohol. Then, I wash the leaves with a soapy soft cloth. Immediately after I clean them, I cover the plants with a protective Ag-30 ribbon cloth to give them extra protection over winter.

Wash fabric row covers

Plants still growing in your garden that are going to be kept over winter are often covered with row cloths. If these are washed before they are put away, there is no need to wash them now. If you accidentally put them away dirty, give them a quick run through the washing machine before laying them over or wrapping up your winter plants. The clean cloth means there is no accidental introduction of mites or aphids into the greenhouse.

A commercial grower once told me to keep my dogs out of the greenhouse. "Dogs can pick up spider mites on one side of the greenhouse and drop them off on another," he told me. You will not see it happening either. So, as you do your "spring" cleaning this fall, keep the dogs outside.

It is sunny today, so I started cleaning. The darkest days of winter are ahead and I have the time now.

Maybe you are wondering if you ever really need to clean your greenhouse? Inspects hide in cracks and crannies and move around with the movement in the greenhouse. From your pets to ants and even you while you are gardening. Mold grows on wet soil, fungus gnats thrive in damp moss, and weeds produce seeds ready to spring out into the planting beds. So yes, it is a good idea to dedicate a day to spring cleaning when you have the opportunity.

Image of Donnas empty greenhouse

Donna Balzer's greenhouse in the process of being cleaned.


In case you were wondering when we arrived at our hotel near the ski hill, we were in time for dinner and drinks with friends. We told long tales of the cleaning out versus the clean fridge. Our friends laughed and of course, invited Keith to come to clean their fridge any time he was available. It was an impressive and sparkling job done to perfection. 

Whether or not your greenhouse is cleaned to perfection this fall is up to you. I suggest at least cleaning out if not cleaning up. It really makes a difference when you get back in full swing during the spring.