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The first year I started my own seeds indoors, I planted around ten flats of annual flowers and vegetables, growing them on top of my mother’s dining room table (sorry mom!). I was sixteen years old and a fairly novice gardener. When the April showers finally cleared and the bright spring sun came out, I had the brilliant idea of taking those plants – whose only light source had been a modest west-facing window – and moving them outdoors to give them a dose of early May sunshine. Oops! Within an hour, every single plant was fried and I had no idea what I had done wrong. I obviously needed a lesson in how to harden off seedlings.
Hardening off is a simple, but necessary step for seed starters. Growing your own plants from seed offers many rewards – save money, grow varieties not available at local garden centres, and enjoy a steady supply of top quality seedlings for succession planting. But, as I learned that fateful spring, you need to properly harden off your seedlings before introducing them to the ‘real world’ outside.
Why? Simple! All plants have a waxy leaf cuticle that protects the foliage from sun and wind, and seedlings that have been grown indoors – in a sunny window, under grow-lights or under glass in a greenhouse – have not fully developed their cuticle layer and need a bit of time to build up this horticultural suit of armor. Hence, the hardening off process.
How to harden off seedlings:
Hardening off is not difficult and will take about a week in total.
Step 1 – Place the young plants outdoors in a shady spot.
Step 2 – Bring them back indoors again that night (I call this ‘the spring shuffle’).
Step 3 – Continue giving them daily shade for 3 to 4 days, bringing them indoors at night if the temperature becomes unseasonably cold or frost threatens.
Step 4 – By day 4, begin introducing increasing amounts of sunshine each day, so that by the time a week has passed, the plants have become adjusted to full sunshine.
Do you do the spring shuffle?