What I’m about to say goes against traditional wisdom that’s ingrained in nearly every gardener and written about by many a cooperative extension office, but I’m bringing it up to ask a simple question: Why?
Why do we need to wash our dirty pots before germinating seeds or putting plants in them?
To wash or not to wash
I confess that I haven’t washed my plastic containers in years, at least not in the way that’s usually advised. Consult almost any gardening guide and the instructions often include scrubbing the pots with soapy water and disinfecting them with a diluted bleach solution.
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But I, on the other hand… I am firmly in the brush-off-the-dirt, wipe-off-the-gunk camp of annual garden cleanup, and I stack my containers in the potting shed like this, ready for the next round of seedlings. (This is the brush I use, which makes quick work of seasonal clean-up, though any stiff bristle brush will do.)
Occasionally I hose them off to remove any stubborn and particularly crusty bits, or I wash the containers for aesthetic reasons (mostly for gifting plants to friends).
I’ve amassed a towering collection of plastic seed starting pots, gallon pots, six packs, and seed trays over the years that continues to grow, and I can’t imagine hand-washing (or even hand-soaking) every single one of them at the beginning or end of each season.
It seems like a silly waste of effort for not that much benefit, at least where pests and diseases are concerned. (If you’re the type of person who loves to clean, however, then none of this applies to you.)
Why, then, are we told to wash our containers at all?
Do pests and diseases linger on unwashed pots?
One popular argument states that washing pots supposedly reduces the chances of damping off disease.
But researchers now know that to be untrue. The conditions that cause damping off (humidity, excessive moisture, and poor air circulation) originate not from dirty pots, but from poor growing practices like spacing seedlings too close together, overwatering or watering the leaves, and leaving plants in non-ventilated greenhouses or under plastic humidity domes and cloches.
In short, your seedling is more likely to develop damping off because of you rather than a dirty pot.
But can washing pots prevent other fungi, bacteria, or pests from hitching a ride on your new plants? Isn’t washing pots a part of good plant health management?
Maybe, and sure, to a certain extent—but neither reason can justify the colossal pain in the butt of washing a pile of pots in the sink, two or even three times when all is said and done.
While pests and diseases can certainly transfer from an old plant to a new one, the chances of that actually happening are slim.
There may be the rare occasion that a dirty pot harbors root aphids lurking in leftover soil or spider mites hibernating under the rim, or perhaps a plant you tried to grow in the pot was plagued with allium rust or clubroot.
If any of that were the case, and serious enough to warrant consideration at all, don’t bother with washing and disinfecting that pot. It’s far more economical to throw it out and use a brand-new pot with brand-new soil instead. The time saved and peace of mind earned is worth the couple extra bucks to replace it.
As for terra cotta pots: Salts and other minerals that build up on the outside (usually at the base, and caused by fertilizers or hard water) can be unsightly and can sometimes hinder proper drainage if left to accumulate. Those are about the only reasons you’d need to scrub and wash them with a stiff bristle brush.
Otherwise, the fear of disease running rampant among dirty pots is really, truly overblown.
Should you disinfect plant pots?
The common advice for disinfecting plant pots is to use a household bleach containing 8.25 percent sodium hypochlorite, and dilute it to a 10 percent bleach solution.
But that dilution amount (8000 ppm, or parts per million, more than even the disinfectant level recommended for hospital settings) is insane. It’s overkill and not something you want to be standing around and inhaling all day.
To put it in perspective, the bleach dilution recommended for cleaning up spills of bodily fluids (like vomit or diarrhea) or disinfecting hospitals with Clodstridium difficile infection is only 5000ppm.
So please, do not disinfect your garden pots with a 10 percent bleach solution.
If you really want to wash your pots at all, hot soapy water is sufficient (and a lot less toxic).
And that brings me to another problem: For the bleach disinfectant to work, you have to wash your pots in hot soapy water first. That means they need to be emptied of all soil and debris, scrubbed with detergent, and rinsed clean. Then you can soak them in a (much milder) bleach solution before laying them out to dry.
You can’t just soak dirty pots in a bleach solution (no matter what dilution it is) and expect them to come out squeaky clean. With the way bleach works, any dirt or organic matter (including soap residue) floating around in the disinfecting solution actually inactivates the microbe-killing power of the sodium hypochlorite.
Bleach also has an expiration date. After a shelf life of six months, it becomes 20 percent less effective with each year that goes by.
Think about it: When was the last time you bought a new bottle of bleach? And how much are you actually disinfecting anything if you’ve been using a bottle that’s been sitting around for more than a year?
Why you should embrace the “dirty” pot
When you think about how plants are grown in their natural environment—outdoors, in the elements, with no coddling from us gardeners—they’re exposed to all the insects and microbes that were there before. Thus, plopping a seed or plant into a dirty pot is no different than plopping it into, well, soil.
How often do you see damping off in your garden? (Not as often as you see it in your indoor seed starting tray, I bet.)
Susceptibility to pest or disease is more an unintended outcome of our own tendencies (to overwater, underwater, sow too soon, sow too late, over-fertilize, or make any other simple mistakes), and less a direct result of secondary infection from a dirty pot.
Viable seeds raised under good conditions (where light, moisture, and air circulation are concerned) produce plants that are vigorous enough to withstand your garden-variety microbes (and in fact, they’re made stronger when exposed to these elements because the plants then deploy their natural defense mechanisms).
This is not to to say I advocate poor hygiene or shoddy maintenance when it comes to your tools and equipment. Proper care of pots and other gardening gear goes a long way toward maintaining longevity and sparking joy when you see everything all clean and orderly.
But the advice I constantly read about washing and disinfecting your pots seems like a gardening myth that’s often repeated but lacking in scientific basis.
What are your thoughts? Are you a devoted pot washer, or merely a dirt brusher like me?
This post updated from an article that originally appeared on August 15, 2017.