In Wisconsin, the general advice for planting tomatoes is to wait until after the last frost date has passed and the soil temperature is at least 50°F. Typically, this means:

• Start tomato seeds indoors about 5 to 7 weeks before the last expected frost.
• For southern Wisconsin, planting tomatoes outdoors usually happens in early May.
• For northern Wisconsin, planting may be delayed until early June because of the later last frost date.
• Southern Wisconsin gardeners often start seeds indoors around mid to late March.
• When transplanting outdoors, tomato plants should be hardened off (gradually exposed to outdoor conditions) for 10-14 days beforehand.
• Avoid planting tomatoes too early to prevent frost damage or stress from cold weather.

In summary, tomatoes in Wisconsin are usually planted outdoors between early May and early June depending on the region, with indoor seed starting in March or April to prepare seedlings for transplanting.

For more precise timing, check your local average last frost date and plant tomatoes outdoors about a week after that date to be safe.