Giving seedlings the cold treatment.
 

Following the cold treatment advice I thought I would make a start last night, but to gradually reduce the temperature. I am using a propagator and have some additional greenhouse heating, but trying not to set the temperature for this higher than necessary. I set the propagator temperature(for soil temp) at 14C(57F). I put a max/min thermometer in as well as seedlings and the air temp got down to 8C(46F). In the other propagator containing the younger seedlings set at 17C(63F) the min air temp was 14C(57F).
It is obviously difficult to maintain a soil temp close the air temp without considerable extra heat in the surroundings. Of course if I choose not to heat the greenhouse any more the dilemma is whether I should set the higher soil temp for the 'cold' seedlings or for the younger ones! Any ideas?
Gill

Gill, keep us updated how your cold treatment works out and if you can take any pictures, please do and post them. Ami

I finished cold treatment today. Plants look healthy and have a purple tinge due to lack of phosphorus. Temperature was constantly 11C/52F. Now I have to wait till fruit set to see the benefits of cold treatment.
Here's the photo, it's the six pack in front, that was in cold room:

Marko, very nice plants with thick stems. I think you will notice a difference in the first fruit cluster.;) Ami

Interesting. I've heard hardening off produces better plants, but it is interesting that it actually increase the blooms and produces earlier harvests, since all I've ever read was about stem thickness and hardiness. I guess it makes sense!

I have been doing this for years.
My room where the plants are grown has the damper closed to the heater and the garage is not heated, any day that it is 40 or above the plants are outside.
The only time they come inside is if there is a chance of freeze or frost.

They get this till it warms up and then they get planted.

The reason I do this is out of necessity. The plants come out looking great.

Worth

My plants have gotten the cold treatment out of necessity, and they look fantastic. It's only my first year growing but they look much much better than the plants I bought from the nursery last year.

I can't comment on the fruiting, but the plants are definitely robust and sturdy.

Interesting topic...

I've always babied my plants that I have on a rack with 16 hours of artificial lighting, until about the last 2 weeks where I acclimate them.

This year I'm using heat mats to help germinate my peppers better, so if I were to try this technique I would use the heat mats until they have true leaves then stop the supplemental heat?

Basically we're throwing them outside once they get their true leaves as long as there's no threat of frost right?

interesting thread, I start my seeds in the basement on heat mats, once germinated they go under lights for 12 hours a day, I have a thermostat in the basement and keep it cool at about 50 degrees, and normally the seedlings do fine until they are potted up then a few weeks later taken outside to acclimate them to the sun and different temps. This year, I'm not too sure what is going on, the seedlings don't look all that great, the room is cool but even though they don't have true leaves yet, I just might pot them up into different containers, 16oz. cups. Am I rambling? LOL, I think I am, so let me end now, :)
Alberta

My seedlings did not do as well this year. Everything was done the same way with the same products. Oh well, we can't control Mother Nature.

Neva

This cold treatment sounds interresting. This year I started 400 plants from seed. I started them all indoors under lights and when I transplanted them to larger pots all the plants went on the back porch because there was no more room inside. I had a space heater on the back porch just to keep the plants from freezing. I was not aware that there was a cold treatment method but my plants grew great this year. Best year I ever had. I was telling my babies sorry that it is so cold because I thought tomatoes love it hot. I am building a greenhouse to start more plants but I cant afford much heat. I am beginning to like this cold treatment method, I will study this more and I am going to ask around, how do the big boys do it.
Joe

Study carefully before you do this. It is dangerous if you don't watch carefully and know what to do.

The "big boys" do tomato plants by growing them in huge greenhouses that never get below about 70 degrees. A tomato plant can be forced to salable size in 5 weeks at this temp and that is exactly what the "big boys" want. Unfortunately, these plants have never been stressed and when you set them out in the garden, they sulk for 2 or 3 weeks before deciding to grow.

Folks like me who grow up to 50,000 plants a year usually are a bit more in touch with their plants. I grow in a greenhouse and I definitely use the cold treatment methods when feasible. There are a few gotchas that you must know how to avoid. The first is that low temps significantly slow down plant growth. Allow an extra week or two for cold treated seedlings to grow. The second is that tomato seedlings are VERY sensitive to excess water. What's excess? You must let tomato plants dry out until they just start to wilt if you want them to be healthy. Give them plenty of water when they are dry, just be sure they are thoroughly dry before you water. The last caution is that you need air circulation even when it is cold. Be sure you have a fan blowing across the seedlings at least part of the day. It encourages the plant to grow a sturdy stem.

Does it work?

I can assure you that cold treatment of tomatoes is VERY effective. It shortens time to first flower truss and boosts overall production.

DarJones

I came across this when looking for information on when a seedling is considered leggy and how to prevent it.

The information on internodal spacing talks about cool temp treatment of seedlings

[URL]http://www.enjoygardening.com/?s=internode+&x=6&y=8[/URL]

Hill60

@ Fusion power:

I'm glad that you stressed holding back watering. Water-stressing has been a part of my hardening off process for years. If you allow the foliage to begin wilting at this early stage, the plant's self defense system begins growing more roots to seek out the needed water. (Bottom watering @ this stage forces a deeper root structure which increases the plant's drought tolerance.)

Last season I had somebody thinking my seedlings needed watering, so they watered the ones they saw. Throughout the season, those plants seemed to need frequent watering, while the ones that they missed seldom needed watering. At seasons end, those that had been "voluntarily" watered early, had root structures less than half the size of those that had been water stressed during hardening off.

DarJones, Very interresting reply. This is good information on "There are a few gotchas that you must know how to avoid". Perfect description. I have printed your post and saved a hard copy when I start my seeds for next year. Thank-You
Joe