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Ask a Gardening QuestionBeginner Gardening Questions & Guides: First time gardener questionsRe using seed compost

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Re using seed compost

#1 · 3rd December 2022, 7:00 am

I know not to re use potting compost as the nutrients have been used but seed compost has or needs no nutrients I believe so can this be re used?

thanks in advance

Wesley

Lee Garden Ninja has reacted to this post.

#2 · 3rd December 2022, 10:30 am

Hello Wesley,

First off search in Lee's Blog, there is a section / video on re using compost.

I re use compost all the time, as an example of what I do, I wish to plant up a two foot deep container, in the bottom of that I would use old compost, the top half or two thirds use new compost, most root systems dont go down two foot, use old compost for plants in the soil as a cover/mulch for tender plants in winter, also you can use this compost on established container plants where they die back in winter, again cover the top of the container with used compost as frost protection, then as the growing season gets under way, remove this old compost, and top up the container with fresh, this should be carried out regularly anyway.

Again check Lee's BLOG, save yourself some money.

Bob

#3 · 7th December 2022, 9:54 am

Quote from Lee Garden Ninja on 7th December 2022, 9:54 am
Hi @wesley
Great question about reusing seed compost. I can see @bob already provided some great advice. Here are a few other vital bits to consider with growing plants from seeds and what kind of compost to use each year.
Can I reuse seed compost each year?
The quick answer is yes, you can reuse this compost but not for growing more seedlings. It's better resued around the garden or for potting on established plants. You can watch my guide for reusing compost below or read about it here.
https://youtu.be/T1vVfz0r0U0
The reason for this is that most seed compost has been sterilised to remove pathogens and any funguses that may infest or damage seedlings as they develop. If you reuse this compost, you end up risking introducing these issues to your entire greenhouse if you are not careful. I'd caveat that by saying if you're just growing a few trays you should be fine. But if you're thinking of growing a lot ie a full greenhouse worth its not worth the risk. Mildew and other fungi in a greenhouse can rip through all your plants damaging them if not careful given the humidity and warmth that allows pathogens to spread fast.
You can sterilise your own compost in an oven, but for most people, that's a bit of a pain. It also kills all the beneficial bacteria too!
I would always start with fresh seedling compost or even homegrown compost that's been sieved. All though not sterile, at least home-grown compost has come from your own garden and should have some resilience to nasties compared to just shop-bought, old and reused compost.
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Alternatives to seed compost:
You can grow seeds in coir or even some perlite and sand, believe it or not too. As soon as they are big enough, transplant to multipurpose compost.
I recommend you watch my how to grow from seed series here to help show you all this in practice.
https://youtu.be/DICGT44SMSs
Hope that helps, and if you like the free gardening advice service that my blog provides, I'm always grateful for a Google review which helps future design clients come my way!
Happy gardening!

Hi @wesley

Great question about reusing seed compost. I can see @bob already provided some great advice. Here are a few other vital bits to consider with growing plants from seeds and what kind of compost to use each year.

Can I reuse seed compost each year?

The quick answer is yes, you can reuse this compost but not for growing more seedlings. It's better resued around the garden or for potting on established plants. You can watch my guide for reusing compost below or read about it here.

The reason for this is that most seed compost has been sterilised to remove pathogens and any funguses that may infest or damage seedlings as they develop. If you reuse this compost, you end up risking introducing these issues to your entire greenhouse if you are not careful. I'd caveat that by saying if you're just growing a few trays you should be fine. But if you're thinking of growing a lot ie a full greenhouse worth its not worth the risk. Mildew and other fungi in a greenhouse can rip through all your plants damaging them if not careful given the humidity and warmth that allows pathogens to spread fast.

You can sterilise your own compost in an oven, but for most people, that's a bit of a pain. It also kills all the beneficial bacteria too!

I would always start with fresh seedling compost or even homegrown compost that's been sieved. All though not sterile, at least home-grown compost has come from your own garden and should have some resilience to nasties compared to just shop-bought, old and reused compost.

Alternatives to seed compost:

You can grow seeds in coir or even some perlite and sand, believe it or not too. As soon as they are big enough, transplant to multipurpose compost.

I recommend you watch my how to grow from seed series here to help show you all this in practice.

Hope that helps, and if you like the free gardening advice service that my blog provides, I'm always grateful for a Google review which helps future design clients come my way!

Happy gardening!