No they aren't the same. Seed starting mix is much finer in texture, usually only contains peat and vermiculite or perlite, and has no added nutrients. Do you have a Wal-Mart or a Lowe's or Home Depot? They all sell Jiffy brand and Ferry-Morse brand of seed starting mix down here.

Potting mix is a coarser mix and the contents depends on the brand but none of the potting mixes contain soil (dirt). They are all mixes of peat, vermiculite, perlite, bark, bark fines, added fertilizers, compost sometimes, etc.

Potting soil is usually screened/sifted top soil(dirt). Potting soil should not be used as is in containers as it compacts too much and drains poorly but it can be used if necessary as long as it is mixed with a great deal of the other components listed above.

You will also see bags labeled "garden soil". That too is NOT for containers but is only to be used in garden beds.

Dave

Seed starting mix is sterile, which helps reduce the chances of fungus and mold. It is also pretty fine, without the larger pieces of dirt/compost/other ingredients in potting mixes and soils, which makes it easier for the tiny seedling roots to grow and spread. Potting mix is just that--a mix of soil, compost, perhaps perlite and/or vermiculite, and some even have slow release fertilizer added in. Potting soil is usually soil with enough lightening agent (peat moss, perlite, etc.) to keep it from compacting too much.
If you have a Lowe's, Home Depot, or a Wal-Mart near you, they usually carry seed starting mix. If not, try a good nursery.

I made the mistake of buying MiracleGro seeding mix. What a joke. Large pieces of twigs and bark. I need to saddle up the horse and head east to a place that sells Fertilome!

Mike

No, seeds starting mix is finer so that roots do not get torn up when you pull seedling apart when separating community flats/pots. It is mostly vermiculite peat moss and a bit of lime/dolomite to adjust pH. Potting mix is coarser and usually contains composted materials such as pine bark and other (originally) woody materials, often with a fluffer such as perlite or styrofoam, and lime/dolomite for pH adjustment. It can be used for starting seeds if you are not planning on pulling the plants out of the mix (I use it for starting everything). Potting soil is often much denser/heavier because it contains actual soil, I have seen it advertized for things that are to be permanently grown outside in containers like shrubs in planters, but someone else might have more info on this than me. Potting mix is usually better for most things than potting soil.

For all of them you would have to check the bag to see if they contain starter fertilizer.

I had a real failure starting seeds in a potting mix. I have now used ProMix BX for several years with excellent results. I think it is billed as general purpose mix. I've used it for both starting seeds and potting up plants. For seeds, I use no fertilizer until the plants are well started and then only a weak solution of soluble fertilizer or fish emulsion.

Jim

Ditto on the comments above. Seed starter (and "plug mix", which is similar) are sterile; so provided that sterile water is used to moisten it, the chances of damping off are minimized. However, these mixes are generally low in fertility, so some fertilizer will be required once the plants start growing. When potting up, I add composted manure to the mix.

Seed starters are not only sterile... they are weed free. If you have ever started seeds in topsoil or many potting mixes, you know what I mean.

The garden shop near me generally carries one of the Fafard soil less mixes in large bags, and I buy two. Glad somebody brought this up, because it's time for me to get some. ;-)