Zucchini plant isn't producing

[Naz2001]

I have about four zucchini plants planted in my pots around my garden. They're in pots, since I don't have any ground space (almost everything is stone). The plants are a good size, and I do fertilize them sometimes with a sort of garden tone. Thus far I have only been able to harvest one zucchini. Another one is forming on the plant. The plant does have flowers, but they either fall of or become brown (dead).
There is also one zucchini on the plant that has different colors. It starts out green, becomes yellow, and the end is brown.
Do you have any tips or ideas for me? This is my first time planting zucchini, and I really want to fix it.

 

[Tjohn]

It's either a pollination problem or blossom end rot, which can be fixed by applying Epsom Salts dissolved in their water. If your plant is just starting to flower, just wait a while until the male flowers bloom along with the females. Sometimes the females get a head start, which doesn't work out so well....

 

[headfullofbees]

The overwhelming problem with courgette fruit is pollination.
Take a male flower (one with a long thin stem), peel the yellow flower off gently to expose the male genitals.
Open up a female flower (one with a short fat stem) & poke the male into the female to pollinate.
One male can pollinate up to four females, I've heard, but would suspect it could do far more.