temperature swings

While I have done some seed sowing in the past I am no expert. I have a large room with large sunny windows that I close off during the winter months (keep the temperature set at about 58). I have a tray of seeds, covered with a clear plastic dome and on a heating mat. I do not trust these inexpensive mats (safety) when I am away at work, etc. Consequently the soil temperature for the tray is in the 70's overnight and when I am home but will drop as low as 56 when it's turned off. Is it realistic to expect the seeds to germinate? If they do or some do, does this temperature swing situation impact their health as seedlings or as they mature.

As seedlings (and after the dome is removed) what would be the typical lowest temperature I could expect them to thrive in?

michaleangelo,
Your soil temperature should be at a steady setting for whatever you are growing. If the seeds require a 70F setting, they should be at 70, 24 hours a day. A swing in temperature will slow the germination process down, an could affect some seeds. I use a temperature control for heat mats, and leave it on 24 hours a day. Once the mat reaches temperature, it suts off. When it colls below the set temperature, it turns on.

"Stay Happy and Keep Gardening"

Thanks for this information Ironsides, but I am not so concerned about the swings in temperature slowing the germination as I am preventing the swings preventing it or killing the seed. I don't really have an option this year about leaving it on when I am gone - I must be turned off. So I am kind of back to square one with this question.

What are you growing? Depending on what seeds you're starting, they might be just fine without the heat mat. If you're starting tropicals then you might not have much luck, but with regular plants you may get just fine germination without the heat.

I don't use a heat mat, my house gets down to 55º at night. Things take longer to germinate, but I get a good % of almost everything. The only thing I've had problems with is impatiens.

If you are growing perennials the swing in temperature is good since many sprout when the temperature flunctuate. However, night temperature should be low, and day higher.
Plants become less spindly when grown cool.

Whether they will germinate in 58F degrees depends on the variety of perennials you are growing. Some will not germinate in high temperature.

Once seeds germinated they are best grown in 60-65 F degrees. Lower temperature won't hurt them. They will just grow slower. Annuals can be grown warmer, and should be.

Thanks much to all for the additional info -- this is what I am wondering about. I have sown both annuals and perennials (mostly annuals). Does anyone know of an online chart that shows the temperature range seed and seedlings can tolerate?

Hi michael:
Here is a site for you to research with lots of links. It is devoted to Winter Sowing. I have also bookmarked other sites that have what you requested and will post the URL here. Have to post this first.

http://wintersown.org/

Here is another great site:

http://theseedsite.co.uk/seedsowing.html

Yet another:

http://grow.ars-informatica.ca/plant_index.php

The last link I think. This one is great. All these links should keep you busy for awhile.

Sorry here it is. For some reason wouldn't paste on the above.

http://tomclothier.hort.net/

I for got to mention the seed company Thompson & Morgan have seeding instructions with the flower seeds they are selling.

Url is www.tmseeds.com

Thank you blomma for taking the time to get all to me.

I wouldn't worry about temperature swings that you mentioned too much. I have stuff in the greenhouse & there was a solid layer on the inside wall of ice. We have a terrible forecast for Sunday thru Tuesday with -30ºC/ -22ºF. I started to put bubble wrap up for extra insulation. last night the outdoor temp was -20ºC/-4ºF & the ice had formed. I put some comforters & a sleeping bag on the roof, so that probably helped. The lowest inside temp at the farthest end from the heater was 7ºC/45ºF. A gazania germinated over night & the impatiens & coleus were fine. pic of bubble wrap install

This message was edited Mar 7, 2009 6:37 PM

Do you run flourescent lights over your seeds? I start mine in the basement and have a problem with cool temps. I can not run the furnace down there and it is usually 58-60. I found some of that 1/2 " stryofoam insulation board in my garage. I covered it with aluminum foil, placed it on top of my lights and around the four sides of the trays. (I taped it together.) It very quickly raised the temp to almost 90. I removed one side of it (too hot and it needed air circulation). It's not very pretty but effective and they will be outside soon (hopefully!). It's very lightweight, so it can be raised easily for watering/viewing. I wish I had thought of this a couple years ago. They have done great this year.

Thank you all for good advice; and Melissa - sounds like a great way to bump the temperature and I will try this.

I'm running into this now too...first it was trying to keep things warm enough and now it's trying to keep them cool enough. got salvia's which are supposed to be around 70? and have light...well, it's warmed up enough here now that if I put them near a window or under lights they get up to 80. Even putting the ceiling fans on if I have them where they get light they get up to 80. If I put them outside on the screen porch it can get even warmer in the afternoon......

Michaelangelo-have you been able to try the insulation board? Any luck with it?