Gardening Tip ~ Hardening Off

1 min to read

Submitted by Jennifer Pyke, a member of the Richmond Hill Garden & Horticultural Society

Seedlings and young plants have only known the comfort of your home or a greenhouse. If you place them outside too early, they will not thrive and may not survive. They need to be “Hardened” to the outdoor weather.

Here’s how to prepare them to do well outside.

Harden them off gradually, so they become accustomed to strong sunlight, cool nights, and less frequent watering. This should be done over a period of 5 to 8 days. Protect them from strong sun, wind, hard rain, and cool temperatures. 

Here’s the recommended process:

  1. On a mild day in mid-May, put them in a sheltered shady location and bring them back indoors at night.
  2. On following days put plants in partial sunlight gradually increasing to full exposure. If temperatures below 10°C are forecast, bring the plants indoors. Warm-season crops such as eggplants, tomatoes, zucchinis, and cucumbers, prefer warm nights, at least 15°C. Water all plants only as needed.
  3. Transplant to the garden in the late afternoon/early evening to allow a cooler settling in, after the last frost-free date, usually the Victoria Day weekend. Water.

When is the last frost-free date?  According to The Old Farmer’s Almanac, it should be May 9th this year and our first fall frost will be Oct. 1st.  Of course, these are not firm dates. Frost dates are an estimate based on historical climate data with the of a frost occurring after the spring frost date or before the fall frost date is 30%.  So, there is still a chance of frost occurring before or after the given dates!  More generally, frost is predicted when air temperatures reach 32°F (0°C), but because it is colder closer to the ground, a frost may occur even when air temperatures are just above freezing. Always keep an eye on your local weather forecast and plan to protect tender plants accordingly.