Our seed starting mix starts in late summer. An old plastic garbage can makes a great place to store some topsoil. If, like us, you aren't blessed with masses and masses of good top soil it pays to purchase a yard or two. I like to fill up a couple of old plastic garbage cans. Place these in a garage or out building, if you are really adventurous you can set up some nice red worms in house keeping and start making compost in the bins!
When it is time to make your mix you will need your soil, some peat moss, vermiculite and compost is nice if you can get it. I recommend mixing this in small batches as you will need a different mix after your seeds are germinated and you move the seedlings to pots or soil blocks.
The ratio I use is 70% soil, 20% vermiculite and 10% peat moss. If you have some compost use that at a rate of 10% and drop the soil back to 60%. It is helpful to check the ph of your soil, if your base soil is even slightly acidic you should reduce the amount of peat moss or add enough lime to bring the final mix up to a neutral ph. Most seeds will germinate best in a neutral ph.
If you are starting fresh this year and have no access to top soil in February, a good quality potting soil at 85% soil, 10% vermiculite and 5% sand will serve you well for this year and be less expensive than specialty seed starting mixes.
I find the vermiculite works better than perlite to keep the soil loose and well draining which is essential to germinating seeds. We broadcast our seeds into soil in the trays, and once the seedlings have their first set of true leaves I plant them into soil blocks or cell packs depending upon where they are going. This way I can provide 'ideal' soil conditions for germination without having to worry about how the plants will grow until transplant time
Next week I will have seedlings ready to move into pots or cells so I will walk you through that mix and the whole process of transplanting delicate seedlings.
Have a great day everyone.