Question
QUESTION: Hi there,
I started tomato seedlings indoors under grow lights in March (I'm in zone 6a in Prince Edward Island, Canada)
The weather warmed up a couple of weeks ago so I put some seedlings into a small, 8' X 8' plastic covered greenhouse outside. Recently the wacky weather has the night time temps dip below zero (about 26F) There's an electric heater in there, but nevertheless when I check the temperature at sunrise it's only about 45 - 50F.
My question is this - although the plants look fine, and become quite warm during the day in their little shelter (goes up to about 68F), I'm wondering if the exposure to such low temps at night could permanently stunt their growth?
-Lissa

ANSWER: Hi Lissa,
Thanx for your question.  Tomato plants suffer damage at 32F/0C, anything lower than that is certain death.  While the night time outdoor temps may be at 26F, the plants are protected sufficiently from being frostbitten.  A temp of 45-50F is sufficient for the plants to stay healthy.

The plants will not be permanently stunted from the low temps.  What happens with low temps is that growth slows down or ceases depending upon how cool it gets.  When I grow tomato, pepper and eggplants from seed, I start them out at a high temp 75F/24C and then after they germinate, I cool the environment down to say 60-65F/15-18C.  This slows down quick growth which can produce leggy plants indoors due to reduced light factor.  It sounds to me like your plants are doing fine.  Once temps warm up permanently about 55F/12-13C, you will see significant growth and your tomato plants will produce just like any other.  I hope this helps.
Tom

---------- FOLLOW-UP ----------

QUESTION: I can't tell you how relieved I am to hear that, Thank you!
I've got one more question about the dizzying world of fertilizing.
I use a seaweed tea to feed the seedlings twice a week. They seem just fine with that but after reading an article about the NPK in seaweed, I'm wondering about augmenting the tea with something that would provide them with more potassium. I'm also leaning toward the "if it 'aint broke, don't fix it" mindset. The plants do look fine, nice and green, sturdy, very healthy looking. Any advice on this perplexing subject would be greatly appreciated!

Answer
Hi Lissa,
Thanx for the follow up.  I would cut back on the feeding.  You can feed your plants the seaweed tea at a diluted strength or follow the directions on the package for nourishing seedlings.  I think once every 7-10 days would be fine until they are ready to go outdoors permanently.  Remember, the more Nitrogen, the more leafy and green the plant is.  At some point, you can use tomato food which will have more potassium and phosphorus for fruit and root growing.  I hope this helps.
Tom