Many a beginner gardener has made this mistake. You go to the garden centre, buy a gorgeous plant, and plant it, only to watch it die within a few days. What went wrong? Perhaps you forgot to harden it off.
Hardening off plants means getting them used to being in outdoor conditions. In Calgary, where I garden, the major spring problem is cold; but plants also need to be hardened off to wind, sun and drought as well. Think of the perfect greenhouse conditions plants are grown in: moisture levels are perfectly controlled to suit the plant, there is high humidity, and the temperature stays even and warm. These plants are not ready to handle the sudden transition to bright sun, drying winds, and cold nights. They need to be gradually exposed to greater amounts of sun, wind and cold before they are planted in the ground. This may sound complicated, but it really isn’t.
First, decide when you will purchase your plants. If you don’t have a proper space with a bright window or grow light, then it doesn’t make sense to purchase your plants long before the last frost. (In Calgary, that’s usually around May 15th).
Find out if your plants are cold hardy and frost tolerant. (Pansies and Snapdragons as well as peas and kale are very frost tolerant, Coleus and Dahlias as well as tomatoes and peppers are not AT ALL.) Cold tolerant plants can be out in much cooler temperatures, basically anything above 5 degrees Celsius is fine. Warmth lovers need about 10 degrees Celsius or higher)
Bring the plants home. If the temperature is warm, find a nice shady, protected spot to put them. If you don’t have a protected spot, an open cardboard box can be placed around the plants to keep the wind away. (This is also a great trick for those times when you MUST plant the plant straight from the greenhouse. ) Bring them inside in the evening to spend the night. (A heated garage also works well).
On their way home, but these bedding plants are used to greenhouse conditions.
A cardboard box can act as a temporary wind shelter.
Each day, repeat the process. Outside in the morning when it’s warm enough, inside at night or when temperatures are too cool. Make sure you water the plants each morning, as they use a lot more water when exposed to drying winds.
A west facing doorway is a protected spot for these pansies.
Gradually increase the amount of sun and wind the plants are exposed to. Once they are able to survive the day in sun and wind, they are ready to plant. The time for this varies: hardy plants are usually ready in a week, tender plants may take several weeks. (It also depends on our weather, as plants I started hardening off in the 20 degree days of April are still not able to be planted in May, because we are still getting cold nights).
That’s it! A simple way to prevent plant deaths.
Happy Gardening!
After being hardened off, these pansies are enjoying their new home in early spring.