Time & Temperature Germination Relationship

19 years ago

Trying to get a handle on the relationship between time and temperature as it relates to seed germination in general.

Seems like most temperature recommendations for germination are around the 65-80 degree temp range for most varieties of vegetables, annuals & perennials.

However, I've seen other circumstances in the form of some charts etc that seem to indicate that temperatures as high as 86 degrees decrease the time to germination which seems like it would be a good thing. I've also seen for some particular varieties of heat lovers that temps as high as 100 are used to speed germination and get greater percentages of germination.

So, if temps fluctuate outside dramatically and seeds still germinate why don't you see higher temps recommended for germination of seed?

Could it be that most of the books and seed pack recommendations assume greenhouse or in house, or in basement propogation and the 70ish temps would be considered reasonably obtainable temps?

Really just trying to get at what I need to worry about and what temps I need to start getting concerned about for varieties.

Any good charts anyone knows of that show time temp relationships for annuals and or vegetables?

Would really like to not worry about unplugging my heat mats as long as I keep temps to say, 85 or below.

Any thoughts?

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Comments (6)

kudzu9
19 years ago
The link below has some useful info. Also, "The New Seed Starters Handbook," by Nancy Bubel, has a great wealth of info on all aspects of seed starting conditions, and a number of temperature tables.

Here is a link that might be useful: Germination Temperature
emyers
Original Author
19 years ago
That's an interesting link..... including the site in general. Lot's of interesting info (Seed starting database for example).

Thanks also for the Reference.

There are SOOOOOOOOOO many variables. For instance. It's really difficult to get a good read on surface temp of soil which is where the seeds are anyway. Thought about this last night when I realized that I was taking the temp around midway in the starting medium. It was much warmer there than at the top surface due to the heat mat. Also, some mist with water and some don't because of damping off potential probs. Some surface sow all seeds.

Temps in the charts I've seen are for an individuals particular "system". Just wonder REALLY how important it is to use 72degrees for one type of plant vs 75 for another. Seems like maybe in the end the difference in rate of germination may be so negligable, that the trouble is just not worth it. Maybe more important to just hold a certain temperature for MOST.

FWIW, I'm just thinking aloud here. No real basis for what I'm thinking yet.

However, I just Had some salvia (farinacea & horminum) & Marigold (African) seeds sprout in two days surface sown with internal soil temp reading at up to 85 degrees. Not sure what the surface temp was then but the reading now with similar conditions is around 78 (by my thermometer which brings up another unknown).
The salvia seeds were supposed to take 12-18 days at 70-78 degrees and the marigold 4-7 at 75-80 degrees. That's a pretty big descrepancy (at least for the salvia). Regarless has me thinking.

Eddie
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kudzu9
19 years ago
emyers-
This is my first year with seedlings. I had enough heat mat surface for 12 standard trays (11" X 20"), but I've only got one thermostat. I think as long as you do a temp in the medium range (I did about 77F-80F) it will work for most plants. I tried about 25 different things at the same time (tomatoes, peppers, eggplants, cilantro, basil, etc.) and got them all to come up in the range of 3-8 days. I think it's possible to drive yourself nuts trying to have the perfect temp for each different specieis.
emyers
Original Author
19 years ago
kudzu-
Yeah, that's basically what I'm thinking too (overdrive myself crazy/er). Seems like maybe 2 or 3 max temperature ranges should get most of us pro or not, where we need to be. Seems like there would definitely be specific temp needs for heat and cold lovers, but what else? I'm figuring germinate at room temp in the house with and without a heat mat for the heat lovers and forget the thermostat. Germinate in the garage with and without a heat mat equals 4 possible ranges probably around 10 degrees apart for the times when seedlings would need to be germinated for transplanting out at later dates whether they are heat or cold lovers. Now the garage temps will not be as stable as the house temps (unless supplemental heat is used) but maybe that's not really a problem since it would be more in keeping with the way nature does things anyway.

Anyway, if you consider that house temp AROUND 70 you end up with the following....
Note however this is AIR temp and I need to look into this further as far as soil temps are concerned.

House with heat mat 80 +/- (relaively stable)
House without heat mat 70 +/- (relatively stable)
Garage with heat mat 60 +/- (will vary without heat)
Garage without heat mat 50 +/- (will vary without heat)

Was kind of thinking that maybe with the HID lighting I could maybe use the heat they give off and in the garage it could be a beneficial thing..... maybe. Only prob, not as controllable as I would like. May end up having to supplement with AC or something in summer. The saga continues.

Would really like to get to where I can do everything (germination included) in my unheated garage, but I'm too chicken to try that just yet.
sallysflowrz
19 years ago
Kudzu9, thanks for the link to Tom Clothier's site -- it's really helpful! And are you from the south, or does Kudzu grow in Washington? I'm originally from Mississippi and it's all over the place down there. I recently lived in Missouri, and kudzu is growing there now.
kudzu9
19 years ago
emyers-
Sorry...just saw your last message today. I think the thermostat is really important if you're using a heat mat. I paid about $35 for mine and I don't have to worry about big fluctuations or overheating, which can be really bad.

sally-
I'm not from the south, but did live there a number of years. I was always impressed by the relentless power of kudzu and thought it would be an amusing screen name...