Hardening-off question

[flowerpower]

A few yrs ago, I had some seedlings out on the deck in late may. I would normally bring them in the shed at night, but I forgot. A nice LATE snowstorm decided to drop about 5 in of snow. They were buried. But they lived and I got plenty of fruit.

[amideutch]

Basically this cold treatment is used to give healthier, more stalky seedlings that will give increased yields and earlier harvests. In regards to light intensity and duration they had this to say.
The tomato is a facultative short day plant which flowers and fruits earliest if the day is not extended beyond 12 hours by artificial light. Young tomato plants do not need the light intensities of full sunlight. Where there is no overlapping of leaves, light saturation is reached at intensities from 2000 to 3000 foot candles, or about one-fifth to one-third the intensity of direct sunlight at high noon. If artificial lights are used, an intensity of at least 500 foot candles should be provided at the leaf surface. Tests with fluorescent fixtures reveal that Wide Spectrum Gro Lux is slightly superior to cool white.
Hope this helps. Ami

[dcarch]

Originally Posted by flowerpower

----------- A nice LATE snowstorm decided to drop about 5 in of snow. They were buried. But they lived and I got plenty of fruit.

It doesn't mean the seedlings were frost tolerent. Here is what could be an explaination:

Pure water freezes at 32 degrees F, but water containing chemicals, salt, etc. will freeze below that, may be 30 to 28 degrees F. Snow is one of the best insulators. If the soil is more than 32 degrees, the snow cover will serve as a "greenhouse" which will prevent the seedling's temperature going below 32 degrees and the seedlings can surive for a long time.

dcarch

[michael4spoons]

Thanks, guys. Also sent this same question to tomatobob.com and Bob Price wrote back with the following answer:
"When we harden off plants, we usually keep them outside in a shaded area during the day and bring them inside a covered area (a garage is great) and let them rest in the dark. It is important that they do not get direct sunlight for several days as it can damage the leaves. A gentle breeze is also helpful as it helps to strengthen the stems."
For what it's worth, last year I put them back under the lights after each round of hardening (one hour; two hours; etc. for a week). Most did fine, but some went yellow. The yellowness could have been due to a fertilizer problem. This year will harden them a bit at a time but do as Bob suggests and bring them into the garage but not put them back under artificial lighting. Will see what happens and report on it here.