With mine it came down to an issue of timing and some years have more hours of cool weather than other years. With the tomatoes, I started the seeds under lights indoors on New Years day come hell or high water. Even as little as two weeks late from that date can have a negative effect on yield. By Feb, I was able to move the plants outdoors and they were still small enough to cover efficiently in the event of a hard freeze or frost. Typically, they will develop flowers a week or two after moving them outdoors. I realize there are differences in the zones here, or even the micro climates contained therein. 20 miles East, or North of me they have an easier time with cool weather crops. Florida is funny that way. Things that the planting charts say to plant can be a month or two off from general suggestions. My approach is really specific to my immediate area and it took me awhile to figure it out.
I also have chard, kale, spinach, strawberries, cauliflower and carrots growing, which are all experimental for me at this time and already I am realizing a need for some adjustments in the schedule for next year. It has occurred to me that the leafy greens that you mentioned are a good bet, but this was mostly spur of the moment and I had committed to what I have, being I was only just going to play with the system a bit this season.
With the old potting mix, instead of throwing it out, I use it to grow sweet potatoes for a couple years. The greens are actually tasty and they require no fertilizer other than what residual salts remain from the previous years after the fertilizer bands have been taken out. This past year, they grew through Spring and Summer, and I harvested about 60 rather large potatoes in October. I am known for my sweet potato pies and also gave away quite a few and they otherwise store for months.
Here's a rather large, "Maryanna's Peace" ( I am not sure if that is the exact name but it's like that) which broke the stem during a knock down in a wind storm that I had to pick a little early. It still ripened regardless. This tomato was actually hidden on the back side of overlapping plants and I would not have found it if not for the knock down.
I too, usually grow tomatoes, but did get a crop of pineapples out of the dormant boxes and old potting mix, that required no fertilizer or very little water or attention from me in my 'off' years.