Giving Seedlings the Cold Treatment

[bower]

Ditto on the beautiful plants.
First blossom megabloom is pretty much expected here. My seedlings always get the cold treatment, and I do think it's a side effect of cold. I've been varying the timing and extent of cold exposure and it doesn't seem to matter...

[Fusion_power]

Megablooms are a symptom of stress. You can induce a plant to produce a primary megabloom by restricting water, overheating, etc.

[geoffrey44]

In answer to an earlier query I can confirm that this method works exactly the same way with chillies (peppers )
I am currently growing habs, Trinidad scorpions and a variety of other chillies under the lights and with the temps mentioned in my earlier post. They are stocky and with the same spread of intensely coloured foliage. They are however much slower growing than the tomatoes which despite the cold are growing at least an inch each week...It is almost frightening !!
Best wishes to all,,, Geoff

[sjamesNorway]

Originally Posted by Fusion_power

Megablooms are a symptom of stress. You can induce a plant to produce a primary megabloom by restricting water, overheating, etc.

I guess stress from overheating in that case. They were moved into a greenhouse after hardening outside. It got up to 90*F the first day, before I opened it up. (Live and learn...) I've since invested in shading.

I've removed the megablooms because I've read that the resulting tomatoes will be misshapen, and not very edible.

[sjamesNorway]

Originally Posted by amideutch

Ever wondered how commercial seedling providers get these beautiful, stalky, plants with thick stems to market? It's called the cold treatment and has been going on at commercial greenhouses for over 30 years. Here's how they do it.

This was taken out of the book "Greenhouse Tomatoes, Lettuce & Cucumbers" by S.H. Wittwer & S. Honma where they recommend 'Cold Treatment' for hardening off tomato seedlings.
The cold treatment should be started just as the first true leaves emerge, whether the seedlings are still in seed rows or pricked-off. Air and soil temperatures should be lowered to 52 to 56 deg F for ten days to three weeks. A ten to twelve day cold treatment is adequate during periods of good sunlight. Three weeks are usually necessary in the fall and early winter when most of the days are cloudy and plant growth is slow. The amount of cold during the ten-day to three week period is more important than the time of day in which it is given. Cold exposure during either the day or night, or both, is effective. Night temperatures of 52 to 56 deg F are recommended when the days are sunny and partly cloudy.
Following the cold treatment, night temperatures should be raised to 58 to 62 deg F. Cool daytime temperatures (60 to 62 deg F) should be maintained in cloudy dull weather. On bright sunny or partly cloudy days, temperatures of 65 to 75 deg F accompanied by good ventilation are suggested.
Tomato plants properly exposed to a cold treatment develop large cotyledons and thick stems, with fewer leaves formed before the first flower cluster, up to double the number of flowers in the first, and often the second clusters, and higher early and total yields.

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

Hi Amideutch. I want to thank you again for recommending the cold treatment this spring. My seedlings turned out to be nice and sturdy, and are growing well after being planted out.

I'm wondering if you, or anyone else, has experienced (as I have) that quite a few of the plants which have received the cold treatment have megablooms as the first blossoms?

Steve

[amideutch]

geoffrey Beautiful plants they are.

Steve Concerning the megablooms I never noticed.

[amideutch]

My bad.

[geoffrey44]

I don't know about the megablooms but some of the plants are developing very healthy looking flower spikes. At this stage of their growth I don't know whether I should leave them or remove them,,,I am inclined to the latter as I believe it is more important to encourage growth rather than pander to their reproductive urges...Any thoughts or suggestions ???
As an aside at Marsha suggestion I tried a dwarf...One of her Perth Pride which she so generously provided... It shows exactly the same characteristics but in a dwarf format...If any interest I will organise a pic showing the comparison...
Geoff

[amideutch]

I don't know about the megablooms but some of the plants are developing very healthy looking flower spikes.

This is one of the benefits of the "Cold Treatment".

Tomato plants properly exposed to a cold treatment develop large cotyledons and thick stems, with fewer leaves formed before the first flower cluster, up to double the number of flowers in the first, and often the second clusters, and higher early and total yields.

Ami

[geoffrey44]

Well here is the Perth Pride which has now been planted out in the garden for about 5 weeks.. Weather has been terrible...coldest July for 20 years ..rain,wind,frost...you name it...we have had it. The plant has been protected from frost and the worst of the windy conditions but fully exposed to all else... It is a dwarf after all !
But looks good...a bit of warmth and hopefully away
it goes...and I think its cold upbringing has contributed to its present healthy stature...
Geoff

[amideutch]

Looking good Geoff.

Ami

[geoffrey44]

Hi Ami
What will be really interesting will be to see what happens when the weather warms a bit... There is always the chance that the plant wont like the change and could well sulk for some time... In which case this all becomes an exercise in futility...
But that fact that the plant is just not sitting and is actually growing in these cold conditions gives me some hope that the advent of warmth will excite it to greater things..
We can but wait and see

[greenthumbomaha]

Snow again tonight but it will be time soon.

I've set a tray by a cold window since I read this a few years ago. I re-read this every year at least twice to the point where I confuse myself! To be sure I miss or forget something, or just need to speed up as the weather has been crazy.

Seedlings are germinated with bottom heat and artificial light until the first few seedlings in the tray appear and then the tray is removed from the supplemental heat source but are still subject to (16?) hours of artificial and/or windowsill light.. someone said 5 hours artificial is sufficient even on cloudy days.

When the first true leaves appear tray is moved to a cool area for cold treatment for desired period.

This is where I get confused. I normally start fertilizing shortly after the first true leaves develop. Should fertilizing be delayed until the cold treatment period is concluded and trays are moved to a slightly warmer area?
Thanks!

- Lisa

[Dutch]

Hi Lisa, I hope Ami checks the board tonight and answers your question.

I just wanted to add that to truly give your plants the cold treatment you should not talk to them and you should try to act as if they are not even there.
Dutch

P.S. Whether using the cold treatment or not, I start fertilizing (bottom watering) shortly after the first true leaves develop using a weak water soluble fertilizer.

[greenthumbomaha]

Dutch, that pretty much answers my question but I didn't see where Ami mentioned fertilizing. Ami is probably in rem sleep about now. I hope we don't give him the hiccups in his sleep.

So weak fertilization during the cold treatment period is part of the process. Just checkin' to make sure they don't cancel each other out. And no bad talk as I bend down to the cold floor to water each of the 72 cells. Got it, thanks!

- Lisa