Need some tips on starting flower seeds in a small greenhouse.?

Use a seed starting mix, or something plain like coir peat in very small pots or a seed starting tray... once they begin growing, transplant into a premium potting mix. Carefully select the potting mix you use, look at user reviews, and try to find the ingredients. Every year or if the plants look hungry or aren't producing well add a layer of compost to your pots, and re-pot when the plant is 2 or 3 times the size of the pot and roots are coming out the bottom. Don't worry about fertilizer, compost has everything, and premium potting mix should feed for several months.

read the advice on the labels. Make sure there is good ventilation and doesnt get too hot, I left my greenhouse doors open tofday and it was fifteen degrees.