Seed starting mixes are as diverse as we have gardeners.
Every seasoned gardener has their own mix that they will swear and very few will consider changing, especially if their mix works. And rightly so.
Some gardeners swear by using prepared plugs like the Jiffy plugs and others will prefer to mix their own from scratch.
Building a seed starting mix from scratch gives you control on what goes into your mix, you can ensure 100% organic content and you can add any additional supplements that you may need. In addition it's very cost effective and you can produce a higher quality product at a 10% of the price of store bought mixes.
At The Seedstead we have a basic mix that we use for all our seed starting, one can amend this as you wish either will different materials or just add extra ingredients to increase the feeding or water holding values.
Our basic mix is as follows.
1 part Coco Peat (buffered or washed)
1 part Vemicasts (Worm poo)
1 part Sifted Compost.
The above is a good general base to work from, and it will suffice as a general seed raising mix. You would probably never be able to buy a mix like the above as the most expensive part is the vermicasts and many companies will not include it at 30%, but just put enough in to say that it contains "black gold" to aid in germination/feeding etc.
To the above mix you can add any supplements that you wish. Supplements can be: Rock Dust, Vermiculite, Perlite, Silica Sand chopped peat moss etc. Standardizing on your own mix gives you that extra pleasure in knowing your starts are getting the best of the best from day 1.
We like to include vermiculite and about a quart of organic fertilizer that is high in potassium to stimulate root growth in your young seedlings. Note that if you are going to include a fertilizer, then add this to the water when you are expanding the coco peat brick. The hollow fibers of the peat are highly absorbent. They will absorb the fertilizer, easily holding it in place so that it does not get washed out when watering.
With your compost portion, if it's your own, you will know exactly what went into it and you can rest assured that they are no Ag chemicals in the mix, alternatively buy from a reputable source and make sure it's well broken down.
We have found in tests is that vermicasts increase the total germination
percentage of seeds sown, and it reduces the incidence of damping off
due to cultural techniques.
When buying your Coco peat, firstly make sure it's from a reputable source. The best coco peat is from inland sources on the Asian subcontinent. Ask for washed or buffered coco peat. This should have an EC value of 0.5 or lower. And higher than that and it will lock out nutrients. Buffering yourself can be done, however it's far more work than the minuscule cost saving.