The weather agency said plants could be damaged or destroyed as a result of the conditions, and advised residents to cover up plants.
Global News meteorologist Anthony Farnell said “unseasonably chilly” air that has been over the Prairies is heading east towards the Great Lakes.
“Below seasonal temperatures and even some late-season snow flurries are likely tonight and early Wednesday,” he said.
“The temperature will also drop below freezing just about everywhere tonight and again on Wednesday night.”
According to the Environment Canada website, the average low around this time of year in Toronto is about 3 C. But overnight its expected to drop to 0 C and then -2 C on Wednesday night.
Farnell noted that sporadic advisories have been issued due to differing criteria depending on the area. Advisories are also in place for the Windsor area and Niagara Region.
“The growing season start date criteria in these areas is technically April 25, so any time where frost is likely after that date, an advisory is issued,” he said.
“The other regions not covered under a frost advisory will still see frost but the growing season still hasn’t begun.”
Farnell said warmer weather will move in starting this weekend.
“But most gardeners know that you can still get frost well into the month of May, even in Toronto or across southwest Ontario,” he said.