Elaine, I've done it both ways with EB's ... when I could get good coir, I've used the same mix for 3 years with no problems. Like so many things, that good coir is no longer available, or at least I can't find it. Found the same brand, but it's definitely not the same coir. Black Gold has a coir that they say is salt-free, loose and ready to plant, but I haven't tried that one yet. Like everything in their brand, it's on the expensive side. Other times, using regular potting mix, I've removed the top 2 or 3" and replaced it. I really couldn't tell any difference from the boxes I did nothing to. Maybe it depends on what has been grown already? Another thing I've discovered with the potting mix I had to use here in FL ... the pH was already on the high end, so I skipped the lime. And, being the maverick that I am, I've even skipped the fertilizer strip and just added liquid fertilizer down the watering tube on some boxes. Truth be told, I think the plants do better with that approach. In the past for tomatoes, I've put crab shells in the bottom of the EB's for the extra calcium. The tomatoes seem to appreciate that. I think egg shells would serve the same purpose.
Summer here this year was hotter than normal too. I blamed most of my problems, especially with the tomatoes, on the extreme heat. I know usually above 90° blossoms won't set. I just think that volunteer knows it's time to start growing again. just like the seeds that the wintersown people set out in milk jugs in the middle of winter. When the weather is favorable, they sprout. I intend to do everything I can to grow this little guy to maturity. But, with that being said, I don't see this as a way to get tomato plants for fall planting on a regular basis
