Hardening Off Greenhouse Plants

Bedding Plants at Dutch Growers Greenhouse

Hardening off is the horticultural equivalent of flossing your teeth. You know you should do it… but, do you?

Greenhouses are a great places for plants. The temperatures are warm and constant. There is freedom from wind and the plants receive regular feedings of fertilizer. The real world… Not such a great place. Plants need to be gradually acclimated to the realities of the garden.

Feel the leaves of a greenhouse plant and you’ll notice that they feel soft. Next, check out the plants that have sprouted in your garden. The leaves will feel firm. On the cellular level, the greenhouse plants have longer plant cells and a thin cuticle or skin. The hardier plants that are growing outside have shorter plant cells and a thicker cuticle or skin. In practical terms, the plant that's been growing outside has toughened up enough to endure the Saskatchewan winds, cool evening temperatures, and depending on the variety, even a slight touch of frost. The greenhouse grown plants need to toughen up.

To harden off greenhouse plants, start by placing your bedding plants outside for just a few hours during the day in a sunny protected spot. Increase the time as the plants toughen up. Make sure that the plants do not dry out and remember to bring them in at night. Most plants will require 5 to 10 days of hardening off.

After you plant your bedding plants outside, listen to the weather. If frost threatens, cover all tender pants with blankets or newspaper. Don’t use plastic.

I became a firm believer in the benefits of hardening off about 15 years ago.

I'd faithfully hardened off my flowers, but when I went to plant, I was short a few flats. So, rather than hardening off the new plants, I popped them in the flower bed straight from the greenhouse.

The plants that were hardened off were sturdier and put on new growth much more quickly than the plants that weren't. The plants that weren't hardened off took about a month to really catch up. Hardening off, it's a little extra effort, but definitely worth it.

© Dutch Growers Garden Centre Saskatoon Ltd 2007

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