Not knowing your conditions, 2-3 hours of water a night seem to be excessive.

I get more zucchini I can manage with two plants, I can't imagine 20!

How long have your plants been in the ground and are you getting both male and female flowers? When you say "smallish," did they not get polinated, or did you just pick them early?

Here is a link that might be useful: The Corner Yard

how can you tell if the flowers are male or female?

I water like that maybe once a week. Before I didn't do it at all... and believe me... it needed it... badly....

It hasnt rained in 6 weeks or so....

The plants have been in the ground around 3 months...

Like I was saying... the green variety started producing and then quit... the yellow variety never produced anything yet.

The female flowers have a baby zucchini at the base of the flower. So it is just a little immature fruit. The males just attach directly to the stem. When the flowers open the reproductive organs of the female flower look like a small yellow flower, there it is kind of folded looking and there is a hole in the center. The reproductive organ of the male flower is just spear shaped and if you touch it with a paint brush pollen will come off.

my zuccini does super in super harsh conditions. high desert soil. mine got (if I let them) 2 and half feet long last summer and they looked like watermelons! They kept surviving with dozens of leaf hoppers... but I will tell you this, don't care about them too much... I was so stoked about my corn last year, they took an aweful back seat and they and my spagetti squash went nuts.. I'm still pulling frozen bags of this stuff out of my deep freeze! Oh, I will say, they really went nuts late summer early fall, they were starting and doubling and tripling in size by the day, I just couldn't keep up! Just give it time.

I had this same problem last year and my plants were only producing male flowers. I have no idea how you can make them produce female ones. This could very well be the issue. I would go out and inspect the flowers and see if you see a little fruit at the bottom of the flower, like theonebluegecko recommended. Good luck!

I'm just outside of Houston like you are. I was thinking the same thing with my zucchini and it's just recently, like in the last week, started producing. The female flowers are way down in the middle of the stalk which is why it's hard to see them. That's also where the zucchini form so it's very easy to miss them. By the time I noticed one of mine it was 9 inches long! I think they're just now really taking off in our area.

It sometimes takes a while for things to get in synch--but I have never heard someone say they didn't get enough zucchini (barring SVB, of course!)