Potting Mix-up

Soil-less potting mix

If you know the difference between potting soil, potting mix and soil-less (or soilless) potting mix you could be mistaken for a master gardener. Now how impressive is that? 

This post could easily become a long essay, which I’ll spare you. What is most important now is to know that there is a very significant difference between potting soil and potting mix. It is pertinent to growing both edible and decorative plants in containers either indoors or outside. 

The subject has been in the blogosphere recently. Poor Deborah, for instance, was put through the agony of mix versus soil confusion recently. Read about Deborah Netburn's heartburn over what to put in her EarthBoxes. Lesson learned. Never listen to a nurseryman (just kidding).

So, here's some dirt on no dirt. 

Potting soil is for planting in and amending the ground. Potting mix is for growing plants in containers. Potting mix has no "dirt" in it. Soil-less potting mix is often called “artificial”. If the ingredients are artificial, whatever that means, does that mean they're not real? 

Without getting into brand specifics, do not use potting soil for plants in containers. Use a potting mix for containers. 

Peat moss, coir, bark, perlite and vermiculite are some of the "artificial" ingredients used in potting mixes. It seems everyone has his or her favorite recipe for a good potting mix. 

For those wise enough to sub-irrigate it's important that the 'soil' ingredients have qualities to promote good capillary action. Dirt doesn’t do it! 

Comments

[Ryan Enschede]

Hi Bob, I found your site via a reference on Brownstoner - I have been developing a rooftop container garden over the last couple years and am very pleased to find the info you have here.

I have a question which is related to the above: we have to give up our terrace for a year for a construction project, and I am wanting to store the potting soil and re-use it as it was a lot of work to accummulate and enrich - it is all commercial potting soil that has been combined with compost, peat moss, and fertilizer. Is this a good idea, or does the soil "die"? Can it dry out without damage? Does it need daylight? I was thinking of leaving it with worms in it for a year's worth of castings... Any knowledge in this area? You can email me at ryan(at)ryanenschede(dot)com if you like.

[browse]

I'm building a 3' x 6' raised garden bed, and would like to build a sub-irrigation system to water it. My current plan is to place several lengths of perforated, corrugated watering pipe along the bottom of the bed, with a PVC fill-tube. Cover the pipes with ground-cover cloth and then cover the cloth with... and here's my question:

Even for a bed this size, do I need to fill it with potting mix to get the proper capillary action from the water/oxygen reservoir? No potting soil, no ground soil from the backyard? Filling a bed of this size with potting mix is going to get pretty darn expensive. Would ground soil mixed in with peat moss be a reasonable solution?