I have a collection of old pots that I reuse again and again for seed planting. It is important to wash and disinfect them well to avoid diseases that can kill seedlings. I washed a big stack of 128-cell seed trays the other day. This should be all of the pots I need for seedlings this year.
It is important to wash and disinfect pots that are reused to raise seedlings. Molds, fungi, and pathogens can remain on the pots. Germinating seeds and small seedlings are highly susceptible to damping off, a condition caused by fungi and molds that kills seedlings quickly.
It doesn’t take long to wash the pots. I have experienced whole trays of seedlings dying from damping off disease when reusing dirty pots. I’d rather that not happen again.
To disinfect pots:
1. Wash with soap. Use soapy water and scrub the pots gently. The plastic of many seed starting pots is fragile so I usually just use my fingers for this task. I set up a bucket in the sink and start scrubbing and rinsing. This year I used a large plastic box that was big enough to submerse a 10×20-inch seedling tray.
2. Soak in dilute bleach solution. Dilute bleach 1:600, which is 2 tablespoons of standard household bleach (8.25%) in one gallon of water. I soaked my trays for one hour in the bleach and then rinsed again.
Alternative method: Run the pots through the dishwasher. I have often done this and it is easy and works well on small pots. Remember to rinse the dirt out of the pots well before putting them in the dishwasher.
Larger, vigorous plants are much less susceptible to damping off, so I only disinfect pots that I am going to use for seed planting. When transplanting established seedlings to larger pots, I don’t clean the pots.
I used to use a much stronger bleach solution for soaking my pots – a 1:9 dilution. This used to be the recommended dilution, and many sites still recommend this. But some really really well researched sites now recommend 1:600. In particular I like this blog post: How To Wash and Disinfect Gardening Pots by Northeast Edible Life. She has very good explanations about why the lower dilution is better to use.