The Q&A Archives: Tomato Seedlings' Leaves Turning White

Question: I've started Burpee Big Boy seeds in soil-less potting mix in peat pots under grow lights, and now they are about 5" high. They've been outside in direct sun during the day (I take them in at night) for the past 3 days (as I attempt to harden them off). Daytime temps are in the 70's and sometimes in the 80's. I keep them well watered, but not soggy. The leaves are turning white. What's happening? I have another variety that I'm growing that is the same size, but those are fine.

Answer: Unfortunately, I think your plants are suffering from sun and/or wind burn. It is important to do the hardening off very gradually over about a week, beginning by placing them in a sheltered location out of the wind and in only a little early morning sun. Each day move them to a slightly sunnier location until they are in full sun all morning. At the same time, allow them to dry out (very slightly) before watering deeply in order to wean them from their coddled life indoors. This allows them to become accustomed to the real sun and some wind without shocking them.

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