paulrph1 Loc: Washington, Utah

Born here so am not a casual visitor. We have 5 N.P. here Zion, Bryce, Canyonlands, Arches and Capitol Reef. Some are high in elevation and some are low in elevation so an ideal time for visiting has it limitations. We also have an easy access to the North Rim of the Grand Canyon but a long way around to the South Rim. To visit Zion the best time for fall foliage would be late October but the higher Parks like Bryce would be best in Late Sept. None of the Parks have a great flower show at any time. The are all mostly evergreen trees with red rocks but are spectacular. I hope if you visit Zion you are fortunate enough to experience it during a rain storm the waterfall are stupendous. Bryce Canyon is best visited and viewed at night during a full moon. Go to Sunset point for an erie view. Seeing all of them would be phenomenal task. This state is vast and the distances are huge and the parks themselves are vast with much to see. Arches and Canyonlands are close. Bryce and Zion are in proximity. It would take a good two weeks to even start to get an inkling.
But come and stay and enjoy.

MtnMan Loc: ID

I also like Natural Bridges.

And there are many areas outside the National Parks that are equally beautiful. For example Lake Powell and Antelope Canyons.

I learned a bit more about that thanks to the idiots in Washington D.C. when we left for a two week trip on October 1 in 2013. Despite great effort by the Obama team to spend money to keep us out of things like roadside pull offs we still had a great visit.

waykee7 Loc: Cortez, Colorado

I've hiked Coyote Gulch, a tributary of the Escalante River, three times in late May over the past 10 years and that seems about perfect: good wildflowers, lots of spring greenery and flowers. But by that time (last week in May) Zion is getting toasty. And the high country, such as Hell's Backbone is likely to still be cold. Capitol Reef is likely to have warm weather too.

wmclark43 Loc: Fruitland, Utah

Hi-
I also live in northern Utah and went on a job in Kodachrome State Park for a few days. It snowed (1-2 inches) one night and the white snow on the red rock was worth the whole trip. Took pictures with a point and shoot - some of the best I have ever taken.
Forgot when I went but it had to have been in late winter or early spring
All the other replies are true of the National Parks. I think you could spend a lifetime in Zions and never see it all
Bill

jeep_daddy Loc: Prescott AZ

I'm going to Moab to see Canyonlands, Arches, and Capital Reef National Parks April 9,10,11. Click on the download link and when the document opens click on enable editing, for the Word Doc that was sent to me by the club I belong to for a bunch of information on what to see there. More that you can imagine. It would take a month to see it all - maybe longer if you wanted to get landscape images in good light. Good luck.

Attached file:
(Download)

LennyP4868 Loc: NJ

The fall is best. But if you want to get blooms you have to go in March. I like the colors and where the sun is at time of year. I would bring at least one wide angle and a super zoom lots of animals

alfaman

Have been to Bryce and Zion in Nov. 3 years ago. Cold and some snow at night but beautiful during the day. last year (late May, early June) spent two weeks and visited five National parks. What worked for us was to spend 3-4 days in an area and take day trips to the parks near by. Moab worked for us as there is much to see near by plus good restaurants and even a camera shop. There is a park called Dead Horse Point that is a MUST SEE. It is off the beaten path. We were turned on to it by a park ranger. You can also write to Utah state parks and they will send you raft of information.
I can't wait to go back
Have a great trip!
Alfaman

backroader Loc: Wherever we park our motorhome

Been there more than once in both May/June and September/October. It was wonderful every time. It started getting a little warm the one time in June. When you go, don't miss some of the lesser known out of the way places also. Goblin Valley State Park and the whole surrounding area is really nice for geology, slot canyons and unbelievable rock formations. Gooseneck State Park is a must see along with Moki Dugway and Muley Point in the same general area. Capitol Reef, Bryce and Arches are my favorites from the more well known parks. Vermilion Cliffs and Grand Staircase are also great areas, in fact my very favorite places, but difficult to access without 4-wheel drive. Finally, make sure you drive Highway 12 from Bryce Canyon to Capitol Reef! It is the most beautiful highway we have ever driven as full time RVers and travelers.