Maybe you started your springtime planting early this year because April was so mild. If that's the case, you'll want to cover up your plants tonight with newspapers or sheets because the temperatures are falling to around zero overnight under clear skies.
And the freezing temperatures and light winds will combine to leave frost on the ground for Monday morning.
Environment Canada has issued a frost warning for much of southern Ontario. Extensive frost is likely across a large area, including Windsor, London, the Greater Toronto Area, Kingston, Ottawa.
Around Toronto, the frost is most likely in the suburbs.
Frost is likely to reappear again on Tuesday morning from the Golden Horseshoe to Ottawa.
If you spot frost on your lawn or garden on Monday morning, we'd love to see a snapshot. Upload your weather photos and they could be posted on our website or shown on TV.
And if you have a green thumb, don't forget to watch our lawn and garden tips.
For the latest on the chilly start to the week in southern Ontario, tune into the Weather Network on TV. Your regional forecast comes up at the top and bottom of every hour.