how many (weeks) later? i would say that the pot is to small, a 5 gall bucket would be best. not sure if this is of any importance, but this year, my zuch's are not doing well either, so maybe it is not the year for them>>???

2-3 weeks later. Today I went out and the single zucchini looks like it is growing

How do i measure the pot to know the gallon size?

the very easiest thing to do is, run to any hardware store, and they should have 5 gal buckets. lowes, ace home depot...and really the garden soil is just fine if you have more. i would add some more soil to the pot, if you have more add in some coffee grounds and eggshells.....or kitty litter (unused) . and is the guy in full sun?