In containers, it is our job to provide the plant with a medium that provides ample oxygen, water providing capabilities, a good physical support system, AND those missing elements that plants need in order to manufacture their own food. It matters not one whit that there are no dissolved minerals in a soil-less container medium. That's what fertilizers are for.

Your workshop leader, I am afraid, was not very well informed.

Do you know how to do a 'SEARCH' right here in this forum? Go back to the title page (of Container Forums), click on the little 'search' word and type in SOILS. You will find many discussions about the benefits of soil-less mediums for containers.

To boot, it wouldn't take long at all for plants to use the dossolved minerals that may be present in the 'dirt' content of that potting soil they made. And there you are, having to fertilize anyway, but stuck with potting medium that is mucky, bereft of large air spaces, and without the ability to drain rapidly.

A "soiless mix" - whether it be peat/wood-based or inorganic-based (volcanic rock and/or turface, perlite, vermiculite, etc) - allows you a modicum of control regarding what type of "nutrients" to add to it depending on the plant. It's not unlike those who grow using hydroponics where the grower carefully controls the nutrients added to the water based on the plant's requirements.

Basically, the material becomes a substrate that allows nutrients to settle and/or pass through it to become available for the plants.

There are those who would rather not have Miracle Gro fertilizer pre-added to the Miracle Grow mix as an example, as the NPK ratio of that fertilizer might not necessarily be conducive or optimum for the plant that is planted in it.

A lot of people use soiless mix, because it's sterile and less dense than soil. The roots appreciate the light mix, and it's good for starting seeds because it's sterile.

Jenny & barb-

THANK YOU! I'm pretty dense about this stuff, and you helped me to see WHY this stuff would exist and be useful. Excellent points!

Rhizo- I did your search and found a nice discussion on tapla's soil & water retention, etc. A good read. I can see the reasoning behind some (expert) wanting to use this type of mix and 'control' the settings for individual plant types, but your point is also well taken: for general purposes, it would seem that I may need to repot this container into something that has more 'substance' since I- Joe Homeowner- am not in the business of trying to control the environment of 'specific' plants, but want an overall potting mix that provides good nutrition for many plants...then they (the plants) can pick & choose what they want to take from said potting mix. (How's that for a honkin' run-on sentence?!!)

Again....it's up to YOU to add the fertilizer. A good, coarse soil-less potting medium in combination with a good all purpose fertilizer used in conservative amounts is all the 'substance' any plant requires. ;-) It's not RS (rocket science). Oxygen is still one of the most important factors. A coarse textured medium makes growing just about anything easier, more successful, more productive, etc. Even novices find it difficult to fail....yay!!!!!

It does sound like your top soil and dehydrated potato potting medium leaves a greeeaaat deal to be desired, lol. If I may speak on behalf of your poor plants, the 'substance' they need is some BIG stuff....bark fines, perlite, etc. Let there be OXYGEN!

(P.S. terrific run-on sentence!)

I'm no expert either which is exactly why I use soiless mixes or good container mix. My containers are a thousand times better since I started using it. Sure, it's more expensive, but I reuse it from year to year. I let the plants die in it and breakdown over winter. Then I break it up and make it nice and loose again, then mix in some mushroom compost or manure and maybe some peat moss. Whatever I have around. I also prefer it without fertilizer added because some of my container plants, like morning glory prefer poorer soils.

I have found that regular soil tends to harden and compact into a ball not unlike cement over time. I only use soilless mix now.

Tapla is a soil genius. Anything he tells you is good advice.

There is a nut in my garden ME, I like to try different kinds of soil. Last year I ground my oak leaves very fine, and put them in an old plastic bathtub, kept them wet and turned for two months and they were like the potting soil, then I mixed about one third fresh mushroom compost into it and put it in pots. After my vegs. were half grown I added one heaping teaspoon of 10-10-10 fert, and kept well watered and had a very good garden, I kept this soil in the pots all winter and this year just added the compost snd used the same soil this year and have another good garden and will use the same soil next year again. SEE I AM A NUT.