If you're like me, your hands are probably itching right now. The sun is out, you can feel spring in the air, you can finally put on a t-shirt, and the beautiful plants you've been caring for inside are ready to go outdoors. Late May is the ideal time to start transplanting a good variety of vegetables into the garden. But beware: if you take your plants out too early and a late frost strikes, you risk losing them! So, when is the right time to set up our precious tomatoes?

The Magic Date: Myth or Reality?

We often hear about the "May 24th rule" (Patriots' Day or Victoria Day) as the safe date for planting. May 24th is actually an average date suitable for many regions, but it mostly applies to Zone 5 areas (around Montreal and Montérégie). If you garden in Zone 3 or 4, you’ll often have to wait until the end of May or even early June to put out your most fragile and cold-sensitive plants. Furthermore, even on the farm, we like to get a head start with tomatoes, but one year, a major frost right after planting forced us to urgently set up floating row cover tunnels on all the rows. It was a lot of work. The lesson is simple: it is essential to always keep an eye on the weather forecast!

The Real Secret: Relying on your Thermometer

The secret to successful planting is relying on temperatures, not calendar dates. There are two crucial temperatures to monitor:

• Air Temperature: Nights must consistently stay above 10 °C (50 °F). If the weather forecast calls for 4 °C (39 °F) or less, it's safer to delay your planting. In any case, your tomato plants won't grow very well in such low temperatures. If it's too late and your plants are already in the garden, you absolutely must use floating row covers to protect your fragile crops.

• Soil Temperature: We want the soil to be at least 15 °C (59 °F) for tomatoes, and ideally even 18 °C (64 °F) for very summer-loving crops, like melons.

To check the soil temperature, you can use a soil thermometer (which you can buy cheaply at a garden center), or simply do the "finger test." Push your finger into the soil and judge the temperature. If it feels cool or cold, it is probably not ideal for your tomatoes.

Here is a table to help you determine the best time for each of your crops:

Golden Rules for Successful Transplanting

Once the soil is warm enough and you are ready to take action, here are a few tips to maximize the chances of success for your fragile plants:

1. Hardening Off is Essential: Make sure your plants have been gradually acclimatized (hardened off) for one to two weeks before setting them up in the garden. To learn more, you can check outFile podcast Episode 7.

2. Hydration First: It is important to water your seedlings (pots or trays) before taking them out to prevent them from suffering water stress during transplanting. You will also need to water after planting.

3. Plant in a "Water Hole" for Larger Plants:

• For larger plants like your tomatoes (already in 3.5-inch pots or larger), dig a hole and fill it with water. You can even add a small fertilizer, like fish emulsion or compost.

• Plant directly into this water hole and immediately fill it with soil.

• For tomatoes, you can bury part of the stem; this will allow them to form even more roots and develop a stronger root system.

• For smaller plants (lettuce, broccoli), water the soil directly at the base of the plant right after transplanting. Water truly helps new plants establish themselves and reduces shock.

4. Mind the Depth:

• As mentioned, for tomatoes, you can plant deeper (up to the first leaves).

• For most other crops (peppers, eggplant, cucumbers), it is best to plant at the same depth as they were in the pot. This prevents moisture around the stem from leading to rot.

5. Choose the Right Time: Transplanting late in the day or on a cloudy day is ideal. This gives your plants a chance by avoiding the stress of direct sun and accelerated drying out.

Direct Sowing: Crops that Love June Heat

June is also an excellent month for direct sowing vegetables that don't like to be transplanted or that love the heat.

• Cucurbits: Squash, pumpkins, melons, cucumbers, and zucchini can be sown directly in the garden, without needing an indoor start.

• Corn: Although it can benefit from starting in a nursery, you can sow it directly in the garden once the soil is warm enough. Sowing in soil that is too cold can cause it to rot.

• Beans: Another crop you can start sowing at this time of year.

A little trick to speed up the germination of these direct-sown crops is to warm the soil on sunny days using black plastic or tarps. All these mentioned crops have fairly large seeds, which gives the young plant a head start in outgrowing weeds. Finally, don't forget to continue your succession sowings (carrots, lettuce, radishes, turnips, beets, herbs) every two weeks in June to ensure staggered harvests throughout the season. Remember that, even if the urgency to plant is there, you must always act intelligently by respecting the soil temperature and the ambient temperature. Keep an eye on the forecasts and cover your little plants well if the nighttime weather is uncertain. 

Happy gardening!

🪏 Frédéric