You may want to scope-out this site for making organic potting mix:
http://attra.ncat.org/attra-pub/potmix.html

Try this video -- step by step
www.youtube.com/watch?v=-VuBa9_EAbM

Here is a site with ingredients in Miracle Gro
http://wiki.answers.com/Q/What_are_the_ingredients_of_miracle_grow

I would advise against potting mix for growing seedlings. The difference between potting mix and seedling mix may seem minor but, in my experience, it is not. I and a friend had serious failures using potting mix. Pro-Mix BX has not let me down in the several years I have been using it. The reliability is well worth the price. Miracle Grow makes a seed starting mix too.

Jim

Miracle Grow makes several different varieties of "potting mix" so it would depend on which mix it is. Some folks give good reports on a couple of MG different mixes but many report various problems with some of them too. EX: They don't supply enough nutrients for the season as they claim to, the Miracle Grow Garden Soil should never be used in containers and their "moisture control" mix creates problems in self-watering containers.

If you browse through the many prior discussions on soil-less mixes for container growing you'll find that many of us consistently recommend ProMix BX. Metro Mix 360 is another good one. They cost more but are well worth the extra expense.

And of course the Container Gardening forum offers several different recipes for making you own. They also discuss which mixes to avoid and why on that forum so if you are container gardening you'll want to check out the discussions there.

Dave

I'm not going to make my own mix. Where do you buy this mix at? I only need enough to make 60 plants in say a 8 oz. cup.

I tried to buy ProMix locally, but could only find Lambert LM-3, which the Agway dealer told me is the same as ProMix.
Although it says "general potting mix" on the bag, she said that it is used extensively for seed starting. Does anyone know if there are problems associated with seed starting in this mix?

ProMix actually makes several types of mix. Promix BX has some kind of fungi in it that is supposed to make roots absorb water and nutrients better, but is kind of coarse and has small chunks of wood in it that could get in the way of a sprouting seed unless you pick them off. They also make a ProMix that has a type of bacteria in it that kills fungi, which is supposed to help prevent fungal diseases. Then they make a third kind that is finer screened specially for starting seedlings. I have used the first two I mentioned with good results, but I cover the seeds with pure vermiculite. I bought a bail of the last type but haven't used it yet. There is no fertilizer in any of the mixtures so a few weeks after your seeds sprout you might want to start watering with Miracle-Grow or something like it.

I start my seeds in peat pellets , then transfer them to Disposable Dixie
Cups. I fill the cups with Miracle grow Potting Mix. Never had a problem.
I don't use the Potting Mix once they are outside in garden, because it's
too expensive for that. I use a lot of compost in my garden. I never had
a problem growing my seedlings in Miracle Grow Potting Mix. Just watch
not to over water seedlings. These tomatoes below were grown in Miracle
Grow Potting mix as seedlings, and then transfered to garden.

{{gwi:15546}}

{{gwi:15547}}

My mistake. I thought you were only using them for seedlings. If your
using it as your main growing medium, I would supplement it with compost
and extra fertilizer.

I use the Moisture Control mix in cups starting with the first seedling transplant (use Ferry Morse seed starting mix in the cell packs to start the seeds), and it works great. I do give supplemental fertilizer about 1x a week. I wouldn't expect any mix to retain enough nutrients in a tiny little cup like that. I've been happy with the MG mix because it has a finer texture than other potting mixes I've tried, so it works well for the small containers, and the plants seem happy. I had beautiful, bushy tomatoes to plant out last May.

I found some planter's pride seeding mix at Menards. I started my onion seeds yesterday in a cardboard wine box. After I put the water to it I wondered if I shouldnt have used another container. I guess now would be the time to switch it to another container.