The reuse of potting soil debate rages

I really enjoy the debates that gardeners have regarding this issue. For the frugal-minded, it's a no-brainer. The purist, on the other hand, has no qualms discarding potting soil after a single use. So why the difference? And who is right? - if there is a right and wrong.

Here's some background reading [link since removed] if you've never contemplated the question. In summary the arguments feature like this;

Advocates of recycling claim sphagnum peat moss, perlite, and vermiculite, the main components in soilless potting mixes, are mined or manufactured from non-renewable resources. The relatively high price of commercial potting mix is also cited. So, in view of these reasons, they say used potting soil should be rejuvenated and recycled.
Opponents of recycling contend that used potting soil could contain disease pathogens and usually loses its nutrients, porosity and much of its organic content. They also say nematodes may have invaded the container during the past growing season.

Whenever I contemplate this argument I'm amazed that no-one brings the question back to, "Do we reuse our garden soil?" The answer is obvious. Yet, if we considered the debate from this vantage point then we wouldn't really have any discussion, would we?

Garden soil can't be discarded after a single use even though it harbours the very same problems that proponents of single use potting soils argue. However, gardeners know that to continue growing similar plants and vegetables in the same spot year after year without doing anything to improve the soil will in fact reap a whirwind of plant failure. Instead we alternate crops, amend the soil and even leave fallow for a season.

The same logic needs to extend to potting soils. If you were to use the same potting soil for one plant family (for example Solanaceae - tomatoes, capsicums, eggplants etc.) every year without doing anything to the mix then indeed you would face many growing problems.

While I would argue that potting soils can be used time and time again, I would qualify my comment that unless the potting mix were to be rotated through different plant crops or amended after each use, you may as well discard it.

Soil is a medium for plants to grow in. It's where they get most of their moisture and nutrients and it's the glue that supports the growing plant. Each plant will suck out as much nutrients as it needs thereby rendering the soil inadequate again for that plant. Therefore the soil needs to be replenished so that it can accommodate other plants.

We understand this when it comes to our garden soil - so maybe we need to apply it to our potting soils as well.

Posted by Stuart on November 21, 2008 6:26 AM | Permalink | Check to Subscribe to this Comment:

Comments

It would seem quite mad to me not to re-use potting soil somewhere / somehow.
As you say - not for the same crops and preferably mixed with something else. I tip mine in a big trug mix it with compost and then rake it into the flower beds.

Posted by: Karen - An Artists Garden | November 21, 2008 7:18 AM

Hi Stuart, I reuse it in the containers. I amend it, and I use an organic fertilizer a couple of times a season. I've never had any problems, my plants grow and bloom as well as they do in new soil, and I've been reusing potting soil for many years.

Posted by: linda | November 21, 2008 8:24 AM

Whenever I contemplate this argument I'm amazed that no-one brings the question back to, "Do we reuse our garden soil?"

Me too! I always say the same thing. Besides, what if you have a large container garden? Would the thrower-outers really dump five or six large soil bags' worth of dirt into their trash cans? They wouldn't be able to put anything else in the trash that week.

Posted by: Fern @ Life on the Balcony | November 21, 2008 9:18 AM

HI Stuart,
I use last season's soil in the bottom of containers and window boxes, then add fresh potting soil (mixed with peat moss) on top. I've been doing this for many years, and never had any problems.
What I don't save I spread on the flower beds.

Posted by: Kerri | November 21, 2008 9:48 AM

Excellent post Stuart! Cheesehead used to be a big proponent of one use potting soil too. Crazy in my opinion. Why would someone throw perfectly good dirt into a trash bag so it can go to a landfill?

Posted by: Cinj | November 21, 2008 10:50 AM

As with so many things in the world of gardening, gardener's throw away potting soil simply because "The book said so"

Trail and error isn't forbidden. Reuse your potting soil and if you run into problems, then use new stuff. I've personally never run into any problems, so why change it?

Posted by: mrtumnas | November 21, 2008 12:39 PM

Great post Stuart. This is how I do it. I spoil my young ones and then I use a good homehade compost mix later on. I have this rule than I spend the same amount of money on the soil as for the plants (roughly)
and I do have healthy plants :-) / Tyra

Posted by: Tyra | November 21, 2008 5:48 PM

Hi Stuart, I always divide old soil into parts and they go back into several pots mixed with new soil (sometimes bought from the nursery) and manure. That seems to work fine!

Loved going through your post.

Posted by: Kanak | November 21, 2008 8:45 PM

As far as not spreading harmful stuff in the soil, I have heard that you can bake your soil in the oven to sterilize it...

Posted by: Zach | November 22, 2008 1:15 AM

I empty all of my used potting soil into a big bucket and mix in new potting soil with it, wash the pots before planting again. I have had few problems. I love you blog.

Posted by: Darla | November 22, 2008 3:53 AM

If you dont reuse potting soil does that mean you throw it in the rubbish? I reuse mine in the sense that I throw it on the garden - as I have heavy clay soil in some places the potting compost is excellent for helping to break this up - it is also good for vegetables as the nutrients have more or less gone but the structure is good

Posted by: Helen/patientgardener | November 22, 2008 4:16 AM

I put used potting soil in my compost bin. Then it all ends up in the garden again.

Posted by: Jenn | November 22, 2008 6:39 AM

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