Think about you sleeping outside all night. If it is too cold for you it is too cold for many of the veggies J. ‘Cool Crops’ can take a frost – so cabbage, broccoli, carrots, peas, beans, lettuce, onions, radish and Swiss chard can all go out into the garden ahead of the ‘Warm Crop’ plants. Plants like tomatoes, peppers, eggplant and cucumbers will freeze if the temp gets to freezing – plus do not grow well if the soil temperatures are still cold. Safest is to plant after the official frost-free date, for our garden that is May 2 – for Toronto May 9 and for Barrie May 26 (good list here: http://www.tdc.ca/canadian_frost_dates.htm). Now you can cheat – and get warm plants out early – but to succeed you need to be lucky – or careful. Careful means you need to cover the plants at night on cold nights – also consider a mulch to help keep soil temperatures warmer.