Zucchini, Squash End Rot or Pollination
You mentioned self pollinating using a small paint brush. Which one is the male and female flower? Also, for other plants, like tomatoes, what's the best source of calcium you would recommend?
Certified GKH Gardening Expert
Female flowers will have small fruit behind the flower. Here is how to tell a male from a female blossom: https://www.gardeningknowhow.com/edible/vegetables/squash/female-male-squash-blossoms.htm You can simply use a high calcium fertilizer, or add some limestone or calcium carbonate to the soil around tomato plants.