First of all, it definitely depends on whether or not you mulch, and on the condition of your soil. If the soil has plenty of organic material in it, and you have a good thick mulch, you don't have to water nearly as much. Certainly not everyday. Secondly, it depends on sun exposure, temperature, humidity levels, and how long it's been since the last rain. Most plants PREFER an inch of rain per week. To apply that much water to a bed with an oscillating sprinkler can easily take three or four hours, IF you put it on in the early morning before the sun is really hot. (When you water is another factor.)

All that being said, I stick my finger about an inch deep into the soil around my plants if I am in doubt. I rub my fingers together and if I can feel moisture in the top inch, I don't water. If it's dry, I do. How often? When the soil is dry or very nearly dry.

If your baby zinnias were seeded directly into the soil, they should be able to withstand pretty close to the same conditions as your full grown zinnias. If they were plugs from a nursery, you need to keep the soil around them moist for at least the first month.

Zinnias are, by and large, fairly drought tolerant. I have some profusions in a pot. Yesterday in our 100 degree heat, I noticed that I had forgotten to water that pot because they were wilted. I watered well and they perked up by this morning and showed no ill effects.

Donna, thanks!

I am mainly concerned with the zinnia seedlings which I grew directly outdoor from seeds. Right now it is raining and it looks like we are going to get 1+ inches (if it hasn't reached that by now). Then there is a small chance or rain on Sun or Mon.

After that the seedlings will be 3+ weeks old so they should be ok.