When is the best time to plant tomatoes

After you last expected frost date and add a few weeks just in case

Now in spring! What is your Zone?

http://planthardiness.ars.usda.gov/PHZMWeb/

Find out your frost dates here:

https://davesgarden.com/guides/freeze-frost-dates/

And info for planting here:

https://www.gardeningknowhow.com/edible/vegetables/tomato/planting-time-for-tomatoes.htm

Mine have been in ground since March, but with all this wacky weather, my friends in other states have yet to get them planted. For some, it might be a short season.

It depends on where you live and what the weather has been doing around you. Tomatoes like warm soil, above fifty degrees should be good, any thermometer that goes low enough will let you know what the soil is doing. This time last year my garden was tilled and ready to plant, this year, we just got another five inches of snow yesterday, again! More on the way supposedly tonight. There is no definite date to plant, just go by the way the weather has been going.

The first sign that it is the proper planting time for tomatoes is when the night time temperature stays consistently above 50 F./10 C. Tomato plants will not set fruit until the night time temperature reaches 55 F./10 C., so planting tomato plants when the night time temperature is at 50 F./10 C. will give them enough ...

https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-temp-for-tomatoes.htm

Depends where you live, in Canada we usually have to wait until after the May long weekend, it's a short growing season in Alberta!