I live in inner Toronto (Ossington/Bloor). I am preparing Tomato seedlings right now (late March).
Question: When is the earliest safe date to plant the seedlings outside (backyard)?
Thank you for contacting Toronto Master Gardeners. According to the 2022 Planting Calendar for Toronto published by the The Old Farmer’s Almanac, the earliest safe date to plant tomato seedlings this year in Toronto is May 11, based on both last frost dates and moon dates. The following link provides more details and dates for planting other crops as seeds indoors, seedlings outdoors and for direct-sowing seeds outdoors.
It is important to gradually acclimate young indoor-sown plants to outdoor conditions so that they do not die, or their growth is stalled. This process in called ‘hardening off’. For most plants including your tomatoes, this means to begin the process 1-2 weeks before May 11 by choosing a sheltered spot (e.g. an unheated greenhouse, cold frame or a cluster of crates or pots to keep the wind off). Don’t place seedling pots or trays directly on the ground. Ideally begin hardening off on a still, cloudy day with steady temperatures and water the plants before they go outside. On the first day, place the seedlings out for 2 hours, then increase the time by 2 hours on the next day with ideally an hour of direct sunshine in the morning. Continue to gradually increase the length of outdoor time and direct sunshine daily. Thereafter, you can then leave the plants outside overnight if there is no danger of frost and cover them with fleece or row covers for added protection. Then they will be ready for planting. Good luck!
For future reference, see the guide below.