According to the OSU Weather Station in Columbus, the last freeze dates in the last two years were 4/2/2019 and 5/7/2020.  Most for the last 10 years were in April.  But these are historical dates and not set in stone.  The point is to be aware of what it happening and to cover or otherwise protect your plants if a freeze is imminent. That said, most plants don't grow well in cool soils even when the air temperature is warmer.  It takes them some time to adjust.

When you do transplant into the garden, it is best to do this when the weather is cloudy.  Keep them at the same soil depth as in the container.  Water 1 hour before transplanting to keep the roots moist.  Firm the soil around the plant and water again with a high phosphorous starter fertilizer.  And cover if the temperatures fall.

  See https://extension.psu.edu>transplanting-annuals-into-the especially the section on Transplanting into the garden.