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Seedlings: Toughening-up and hardening off  - Cultivate Waltham Forest
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Seedlings: Toughening-up and hardening off 

Seedlings: Toughening-up and hardening off 

Errol Fernandes is the first of our guest community gardeners to contribute to our blog and newsletter.   Here Errol outlines the most reliable way to acclimatise your indoor grown seedlings to life in the open air and all the elements might throw at them.

Errol Fernandes

From your Cultivate Grow Your Own Starter pack, it is recommended that cucumbers and chillies are started indoors;  you might choose to get a head start with your courgettes and your beans by sowing these indoors. For more information about caring for and transplanting seedlings of specific plant varieties Errol recommends the RHS website.

The Cultivate news team is curious to know what acclimatising tricks other local growers have been adopting in these recent weeks of sun and sleet. Please send us yours by email to:,  facebook or twitter!

In order to give your seedlings the best possible chance of growing into mature plants that will flower and fruit, you will have, in many cases sown your seeds indoors during the last few weeks. These plants will need to be transplanted outside once the temperatures are warm enough to support proper growth.

I am writing on a gloriously warm, sunny Friday afternoon in May. However, there was some frost, hail and freezing showers last week. “Hardening off” is the process of gradually preparing seedlings for their permanent position outside.

Your seedlings will be used to the warm conditions in your home, but will start to get leggy as they search for more light. We gradually move the young plants outside for a portion of the day to slowly introduce them to the direct sunlight, dry air and cold nights. Here is a short step-by-step guide to hardening off.

  1. Harden off gradually, over a 7-10 day period. Avoid rushing this process as this will stress the plant and place it in danger of scorching by sun, wind or frost.
  2. On a mild day, start with 2-3 hours of sun in a sheltered location.
  3. Protect seedlings from strong sun, wind, heavy rain and cool temperatures.
  4. Increase exposure to sunlight by a few additional hours at a time and gradually reduce the frequency of watering. It is important not to let your seedlings get so dry that they wilt.
  5. Keep a close eye on the weather forecast and low temperature prediction. If temperatures below the crops minimum are forecast, bring the plants indoors or cover them with a sheet or horticultural fleece that should be secured in position.
  6. Try and be aware of the relative hardiness of the plants that you are growing.
  7. Transfer the plant to a site that suits its preference for shelter, sun, warmth and shade. The RHS website has some sensible and straightforward guidance for each plant variety.

Errol is a Gardener and Horticultural Consultant living in Leytonstone. To contact Errol direct email: