You CAN add soil to containers .... if you want to - It's the wisdom of adding it that comes into question.

It's actually suggested that you do not amend planting holes, especially those in clay and with organic matter. The planting hole becomes a bowl that fills with water each time it rains or you irrigate heavily. If the water remains in the hole too long, or other conditions are right, fungal infections and root rot can set in.

How water behaves in containers is different from how it behaves in gardens & beds. Water retention in containers is directly related to the size of the particles in the soil. When you add clay or topsoil to container media, the very fine particles clog essential air pores & cause high levels of water retention.

For a more thorough explanation of how water reacts or behaves in container soils, see the link below. Hopefully, you'll find enough information to allow you to make your decisions.

Al

Here is a link that might be useful: More info

The link Al provided has lots of great science, Avajay. I highly recommend it and the link I'm providing below. I'll also take a stab at distilling the most important parts of this.

First, as Al said, soil in containers doesn't work the same as soil in the ground. That's really what this is all about.

Soil in a container needs to do several things to provide a good growing experience. 1)Root anchorage - hold the plant upright, 2)Wick water upwards against gravity, 3)Drain water downward to prevent the plant standing in water, 4)To hold onto the "right" amount of water and nutrients, 5) to provide air space for the exchange of gasses.

The particle size in the mix is a big part of how these things above happenÂor do not happen. If they are too large, you sacrifice the ability to hold onto water, for example.

ThatÂs sort of the basics of the why. To get everything you need to happen, the mix has to have certain characteristics. Soil will not have these and youÂll sacrifice at least some of the above necessities.

Here is a link that might be useful: Another link to read; may help with understanding Al's post

I use a soil/peat mix for my containers. You do need to check the moisture levels in the root zone to prevent over or under watering. From reading this list I get the impression that the use of a soiless mix is critical for self watering containers.

From reading this list I get the impression that the use of a soiless mix is critical for self watering containers.

Definitely. If you use dirt in a top watered container (never would I recommend this) you can attempt to mitigate some of the problems with very careful watering, but in SWC there is nothing you can do other than allow the media to wick up as much moisture as it wants to.

Soil in SWC never dries down to allow the tiny spaces between particles to fill with air.

Peat based mixes are the norm in SWC (though I use bark based ones), but even with peat based mixes some have found certain brands to hold too much moisture.

Thanks all,

I guess I'll just use the bagged mix, then. Or make some.

Who knows if a 2 cubic foot bag of mix will fill an 18 gallon tote? I'm planning a trip to Lowes in the next coupla days, it's a half-hour drive. I'd rather get what I need in one trip, know what I mean?

Joyce

Almost, but not quite. You'll be lacking about 3 gallons of soil.

Al

Multiple waterings, over time, can eventually lead to root exposure with container plants. I tend to add an inch or so of "fresh" soil to them about halfway through the year (coming up in a week or so).