I'm growing lettuce and mustard under my shoplights indoors.

I used sterile potting media because they said otherwise the seedlings would be diseased. I know I want nutrients in my salad greens somehow, so I poured some seaweed fertilizer in each tray.

Then I thought, don't plants need soil life in order for them to obtain nutrients? So by fertilizing sterile potting media, is it kind of useless, like small scale conventional agriculture? Will all those nutrients never get to the plant roots without any bacteria or fungi to bring it there? Essentially I want those seaweed fertilizer nutrients to end up in the salad greens, but how can I be sure that will happen?

Thanks for your opinions on this.

There will be soil bacteria, if nothing else some lactobacilli from airborne, microscopic flakes of your skin.

Indoor garden plants are in an unnatural situation. If they had the right sort of mycorrhizal fungi, they might reach several feet down, but I doubt you used potting soil so deep as that. I'm pretty sure the concentrated nutrients you gave them will be enough for their growth, even with a restricted set of soil microbes.

I might say it's a small version of commercial agriculture, but I think it's probably appropriate to your situation. It sounds as though you're in a place where lettuce doesn't do so well outdoors at this time of year, and so green growing things for you to eat will require some sort of artifice. At least the lettuce wasn't grown in a way that pollutes and degrades farmland in some developing country, and then brought to you by air freight and with yards of plastic film wrapped around it.

Another option for small spaces in the winter is to eat either sprouts or microgreens. Sprouts don't need light or soil. In both cases, most of the energy to grow is stored in the seeds; in some ways, it amounts to storing fresh produce in a dehydrated, compact form (some assembly required).

mine in my greenhouse are growing in pure compost over gravel

The sterile potting medium is mostly to prevent damping off disease as the seedlings emerge. By the time they have their first true leaves, most of the danger is past, as long as you're not overwatering and/or keeping the plants too humid.

Whether or not the plants you grow under shoplights are as nutrient dense as those grown in the soil is an open question. You could start experimenting with a refractometer, or you could just not worry about it.

I use an earthbox indoors, so I add a dry organic fertilizer. The plants grow great. For using a liquid fertilizer, I have the best luck by using a weak dilution every time I water. Don't water again until the soil feels just barely damp. In winter conditions, this can mean days between waterings. Whatever you do, don't just dump water on your plants every day.

@ Brenda

Why do you put the compost over gravel? How many times can you throw a round of spinach or lettuce seeds and there without replacing the compost?

@ Jacque

Have you had success growing other things indoors such as flower and herb starts? I've had alot of seed starts like Basket of Gold, False Indigo, and Echinacea die on me.

Plants can absorb enough nutrients to grow even in hydroponic conditions. There may or may not be differences in terms of the health or nutritional status of the plants... that mostly depends on how good of a job one does in making up for nutrients in the low-soil or soil-less conditions. 

I look at such efforts as reasonable and acceptable if they are small scale - small portion of the diet, small use of resources, doesn't take away from pursuing more rational permaculture strategies.  I am considering an indoor grow of basil, as I really like fresh pesto and I find it has a good anti-inflammatory effect on my arthritis. If I were a purist, I would grow something else during the normal growing season and preserve it for use in the winter.

We grow lots of greens, mostly lettuces, all winter here in Minnesota in window boxes.  We use our garden soil mixed with compost and some perlite to improve drainage - the mix is not sterilized.  We refresh the potting soil each fall with additional mix, recycling out the old soil.  We don't use artificial lighting.  The greens are very tender, probably due to the reduced light levels.  Here's a link to our website where we have a photo posted http://www.geopathfinder.com/22601.html .

"Have you had success growing other things indoors such as flower and herb starts? I've had alot of seed starts like Basket of Gold, False Indigo, and Echinacea die on me."

The same issues apply - when you are starting seeds indoors under lights, you must make sure that there is enough, but not too much, water. Watering from the bottom, heat mats, a small fan, all help. You just have to keep tinkering with it until you find what works for you in your conditions. And then, your conditions will change...

Actually, this year I am trying something different - winter seed sowing. Too soon for any results, but intuitively, it seems perfect. http://www.wintersown.org/

i think the best greens you could "grow" inside are sprouts of various kinds. very nutritious, very tasty, very easy. and there is lots of things you can do with them in the kitchen. buy seed in bulk and save big time. no electricity needed, very little space, no soil.

Walk, your site was inspiring - lots of ideas on my to do list. 

Your lettuce looked delicious as well!

Thanks!

why? well the pex from our wood furnace is buried in a mix of gravel and the soil that was there when we dug the trench for the pex..that is why the gravel..it just so happened to be what was there..it is likely mixed with topsoil, clay, sand and whatever else was in our fill beside our house, fill was taken from our field.

compost..well we got a load of compost and i put a whole gob of it in the greenhouse..when we moved the greenhouse there this summer, and spread it out evenly about 6" deep over the gravel/soil mix.

so that is why..and will I replace the compost..likely..but right now the greens and veggies are growing beautifully in it..although it doesn't get enough moisture as it is way below freezing most of the time ..and I am not too thrilled about opening the door to do more than sneak in and get a harvest and water..occasionally..when it is warmer out..so as not to let the cold air in.

Mr.chuck, although I think your plants will still have nutrients, they would probably do better all around if you inoculate with an endomycorrhizal (arbuscular) fungi powder, or with some healthy/lively soil
I know of a good company that distributes mycorrhizal fungi from Portland, OR www.mycorrhizalsymbiotics.com

a year and a half later, update.

The greenhouse is doing fantastically, I have enough lettuce and other greens to supply other extended family members from the greenhouse alone, and I do have greens growing outside the greenhouse as well..My swiss chard in the greenhouse is finally going to seed after 4 years of supplying me greens, and a few of the lettuce plants are finally bolting, they will be allowed to reseed.

it is also full of tomato and pepper plants.

I was also thinking about attempting to grow some microgreens in the house, as I have a lot of them growing outside..over winter..IT would be nice to be able to cut them fresh daily for my salads in the house..and in the winter last year our wood furnace broke down and had to be replaced, so my lettuce didn't flourish as it didn't get the bottom heat all winter..(Feb 29 broke down)..until then I was getting plenty of greens..and will again now as we have a new wood furnace..however, the experiment of growing greens indoors is something I'm considering..i have a lot of seeds from Bountiful gardens like their microgreens and kitchen sink mixture as well as many others.