Virtually all types of squash will produce only male flowers initially. Female flowers may not be present for days to several weeks later.

Someone needs to tell my zucchini that produced 2 females before the first male flowers opened.

Those Amazonian, up-front females have to be handled with care Jack! They ain't looking for a mate. ;-)

Dave

My squash problem seems to be that, at this early point, the girls and guys aren't showing up at the same time making pollination difficult. I've managed to hand-pollinate 2 zucchinis and one crookneck by pulling the stamen out of a yesterday's-blossom.

My yellow zucchini have produced females first but the greens have produced all males.

There is a reason that squash usually produce male flowers earlier than females (but not always!) Pretty smart plants. Female flowers are more energy and nutrient-intensive for the plant to produce. There's a lot of effort that goes into making that ovary fruitlet. So it throws out male flowers first, to attract pollinators. Then it's worth the extra effort to make female flowers once those pollinators know that things are cooking.

Of course, with hand pollination, all you need is ONE male flower if you have female flowers.

Still no females. And it appears the plants have not grown much in weeks. Is this due to the row covers?

As to no females, it's mainly due to bad luck. As to plants not growing much, you need to look harder. Fertilization? Soil quality? Enough sun? As long as the row covers aren't blocking much sun, they aren't at fault. Commercial row cover material doesn't.

I used this: https://www.amazon.com/gp/product/B014G8E6VA/ref=oh_aui_detailpage_o06_s01?ie=UTF8&psc=1