When is it really safe to sow seeds and plant seedlings in the ground? And even in pots?
We often hear that we should wait until there is no longer any risk of frost… but that’s not the whole story. Even without frost, cool nights can slow down or damage certain cold-sensitive crops such as tomatoes, peppers, and tropical annuals.
Planting too early, even if the temperature only drops to 3 or 4°C, can give young plants a cold shock. As a result, instead of getting a head start, your crops will fall behind because they will have suffered from thermal stress.
It’s better to wait a few more days for the nighttime temperatures to be milder to really stack the odds in your favor. In gardening, patience often pays off!
My Crystal Ball… Online!
Here’s how I determine the right time to plant or sow cold-sensitive plants (I include tomatoes, peppers, eggplants, cucumbers, squash, melons, and most annuals in this group): I rely on online weather forecasts. Personally, I use the Weather Network, but there are several other sources that are just as reliable.
Every spring, around the end of May, when the urge to garden becomes irresistible, I start monitoring the 14-day forecast. Obviously, it’s not foolproof, but it gives a good idea of the trend.
What am I looking for? Nights at 10 to 12°C/50-54°F or above.
If I see that the temperature is likely to drop below that threshold in the next two weeks—even slightly—I prefer to wait a little longer. A forecast of 9°C/48°F ten days in advance can easily turn into 5°C/41°F in reality… and a single cool night can be enough to slow plant growth considerably for several weeks.
When the forecast nights remain consistently above 10°C/50°F, it’s the green light: you can plant! (But if you’re the cautious type, wait for 12°C/54°F!)
This Spring
In several regions, weather forecasts may predict nights that are just too cool to safely plant cold-sensitive seedlings. For example, nights forecast to be around 10°C (50°F) for a few days, followed by a sustained warm-up: this is a tricky situation. Almost warm enough… but still a little risky.
In these cases, I opt for a compromise: I start acclimatizing my indoor seedlings to outdoor conditions, but I don’t plant them in the ground right away. As soon as daytime temperatures reach 10°C/50°F (or 18°C/64°F for very cold-sensitive plants such as tomatoes, peppers, cucumbers, and melons), I place them in the shade for a few days, then gradually move them into the sun for 7 to 10 days. And if the temperatures drop, I can easily bring them back indoors—a shed or garage often provides sufficient protection against slightly chilly nights.
Be aware that conditions vary greatly from one municipality to another, even a few kilometers apart. For example, one town may have stable nights at 12°C/54°F, while another, at higher altitudes or further from urban centers, will still experience several cold nights.
Even in generally warmer regions, a single cool night between heat waves can significantly slow the growth of sensitive plants such as tomatoes, peppers, or squash.
In short, always check the forecast for your specific location. If it’s not the right time yet, it will be very soon. And if nighttime temperatures stay above 10 to 12°C/50-54°F, happy planting!
This text was first published on this blog on May 26, 2015. It has been revised and its layout has been adapted.
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I allway check long-range forecasts before planting my vegetables, just like I plan each move carefully in draw climber. Timing and patience make all the difference in both gardening and games that reward steady progress.
I see plants I like order seeds & some come with no name or instructions on planting. What’s best most reliable way to identify seeds?