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Do I need to sterilize my potting mix?

When I did my seed starts, I sterilized the starting mix with boiling water and covered it with foil for 24 hours to kill off any bug larvae etc that may damage the seedlings. I'm about to pot on some young plants with a mixture of John Innes 2 and potting grit. Do I need to sterilise the John Innes like I did with the starting mix? Many thanks!


  • Also, do all store-bought bagged potting mixes/soils etc need to be sterilized before using? Why or why not?
  • All sounds rather anal to me...if you have the time and inclination then go for it. But really don't see what is the major improvement in growing it will actually give you. Most seedlings will stop being in a sterile environment the moment they are exposed to air and the environment overall. 
    To Plant a Garden is to Believe in Tomorrow
  • Nanny BeachNanny Beach Posts: 8,343
    I don't know anyone who does this. Why would there be bugs in a purchased compost? Seeds germinate or not
  • FairygirlFairygirl Posts: 50,133
    No need for any of that   :)
    As @amancalledgeorge says - they have to go outside at some point. It's a bit like endlessly sterlilizing everything in a house to prevent children catching something IMO. 
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
  • BobTheGardenerBobTheGardener Posts: 11,391
    edited August 2021
    It might be worth sterilizing compost in which you are germinating seeds, if you have had issues with the fungal disease called 'damping off', but there is no need to sterilize compost used for potting-on plants.  In fact, by sterilizing, you will also be destroying any beneficial soil organisms present, such as mycorrhizal fungi, so may even make your plants grow weaker and possibly be more susceptible to pathogenic diseases when they are eventually planted out into the garden.

    A trowel in the hand is worth a thousand lost under a bush.
  • DovefromaboveDovefromabove Posts: 82,724
    In 'olden times' books recommending sterilising potting compost because it was made from 'home made' garden compost with the addition of leafmould and loam etc.  The home made compost may not have been hot enough to make any weedseeds etc unviable, and gardeners ran the risk of their germinating seeds/seedlings being swamped by weeds growing around them.

    Bought compost should have been composted at high enough temperatures to 'neutralise' any seeds it contains.  

    Of course that doesn't mean that windborn seeds etc won't find their way into your compost in the seedtrays etc.  That's why it's good to learn to recognise 'weedlings' when they're very small.   Also a good reason to try to sow your seeds in rows rather than randomly ... then you can identify them and remove anything growing that's not in the rows. 
    “I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh

  • Thanks for your advice everyone! Repotted today and skipped the sterilizing. I just hope my young plants will be okay, some were growing together and I had to detangle the roots, I think I may have damaged them a little as it took some doing... They really needed repotting! Hopefully I havent done too much damage and they like the potting mix I made ☺
  • LynLyn Posts: 21,323
    That’s why they say sow the seeds thinly, if you’ve damaged young roots they may not grow for you.

    What plants are they? 
    Gardening on the wild, windy west side of Dartmoor. 

  • FairygirlFairygirl Posts: 50,133
    I agree with @Lyn. Better to sow a few, then do it again a few weeks later. It helps to avoid that problem. Some plants will definitely stand more abuse than others too  :)
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
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