zucchini in earth boxes

I need help I am growing two plants of zucchini and two plants of cucumbers. My problem is my zucchini are growing to about the size of cigars then they turn yellow and stop growing. I started with two plants It has tons and ton of blossoms but none seem to take off before they turn yellow. It looks like I have two plants in one hole but I only planted one in each hole. Can any one help me so I don't loose my whole zucchini crop?
My cucumbers seem to be doing ok. Please help!!!

Linda

It sounds to me that the female blossoms are not getting pollinated. Squash plants have male flowers which are just on stems and female flowers which have a small fruit at the base of the blossom which grows if the blossom is pollinated or turn yellow and dry up if the blossom is not pollinated. Usually bees get the job done in my garden but you may want to try going out in the early morning with a Q-tip, sticking it into a male flower to pick up some pollin off the stamin and then into a female flower which will pollinate the blossom.

Rich