I do know that seeds don't need any fertilizer to spout and have that initial growth spurt. The off brand potting mix I used was good enough to sprout the seeds, but it failed to sustain any growth. I did not use any liquid fertilizer on those plants. Maybe that was the problem.
The year before I used MiracleGro with fertilizer and the plants grew great after germination - without any additional liquid fertilizer. So, I was thinking the seed starting/potting soil should not need additional fertilizer if it was any good.
I have never heard that additional fertilizer in the mix was not recommended for seed starting. I think the soils that I have looked at have a timed-release fertilizer which allows them to feed the plant up to that 6 or 9 months.
I used Mel's mix years ago when I first got into raised beds. I had great results the first year. However, you need to add additional fertilizer's every year to keep the system growing. I found the Mel's mix worked great as long as you were willing to spend the money on fertilizers. But Mel's mix was an expensive way to grow food in raised beds and I started looking for less costly alternatives.
Because of the initial cost of buying all the ingredients for Mel's mix, I was limited to how many raised beds I could afford to fill. The cost of additional fertilizers to keep the system healthy limited my ability to expand my number of raised beds. If budget is of no concern, then Mel's mix is certainly a great method and I did have excellent results. Budget was a concern of mine and I thought there had to be a better, less expensive, way for me to garden. The cost of Mel's mix per raised bed was unsustainable for my budget, limiting me to a small number of beds, and no desire to expand due to the cost.
I started making compost in pallet wood bins and using that instead of chemical fertilizers. That is normally a slow process where I live. But it did allow me to fill additional raised beds.
Over time, I got a backyard flock, converted my chicken run into a chicken run composting system, and make more Black Gold chicken run compost than I need every year - for free. That allowed me to double the number of raised beds I could support, and then I doubled that number again. Each year I have been adding new raised beds, filled with hügelkultur wood, organics, and then a final mix of high-quality topsoil and chicken run compost 1:1.
That chicken run compost has been the magic mix for me, all natural, free and ready to harvest as needed. There is a part of me that really feels great about not having to buy all those expensive ingredients required for Mel's mix and not using chemical fertilizers in my beds. I get the same, or better, results using topsoil mixed with chicken run compost in my hügelkultur raised beds at a fraction of the cost. Chickens and gardening just go together.
I will be looking more into the effects of having a potting soil with timed fertilizer has on seed starting. I am not opposed to using fertilizers as needed for my indoor plant starts. I do bottom water all my seed starting pots as I now use 3-inch net cups as my main method. Previously, I top watered my plants and killed many of them. I have much better results with bottom watering as you suggested.
Here is a picture of the 3-inch net pots which I use to start and grow my tomato and pepper plants for about 8 weeks inside the house. I have had more success with this method than others I have tried. But every year I will experiment with other methods as well. When it comes to gardening, I am always learning...
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