How hot is to hot for seedlings

MrTudball · April 1, 2011

Tried to find this thru search but came up empty, I'm sure the answer is in plain site but I couldn't find one.

I put my seedlings out in my greenhouse for the first time this year. Went out today, outside temp was 52 and inside temp was 90. I can vent if need be, but at what temp does it start to effect the seedlings?

maf · April 1, 2011

Not sure on what temperature will affect seedlings, but if your greenhouse is getting to 90°F it needs venting, at least during the 10 till 3 time of day when most sun is on it. You are inviting fungal problems without sufficient airflow, due to the increased humidity. I vent greenhouses any time they get over about 70.

ireilly · April 1, 2011

I am not contradicting maf's advice but I can tell you that I have had seedlings starting as late as July-August here and it was over 100 degrees at the time.

But - when it gets that hot not much really grows. Even the watermelon and okra kind of just hold their own at those temperatures.

But it does not kill the tomato seedlings. What does kill them is the intense sun drying them out and they flop over from low vascular pressure - if you don't keep them watered. I was watering every day then, sometimes more than once.

So - not ideal, but they can survive. Thrive - not really.

Walter

MrTudball · April 1, 2011

Thanks maf, the humidity was real high.

b54red · April 2, 2011

As long as the plants are adequately watered they can take some really high temps; but maf is right about the high humidity causing diseases to flourish. Another problem with the higher temps on small tomato seedlings is they can become too leggy.

travis · April 2, 2011

Cool, even temperatures promote more stocky seedlings, while high temps will cause the seedlings to stretch out and get leggy when they're still in tight quarters of plug trays. In addition to shorter internode spacing, cool temps between 55 - 65 degrees F at the first through second true leaf stage also promotes earlier, fuller fruit set. But it's not always easy to maintain the milder temperatures in greenhouse conditions unless you have vents, fans and sometime chiller units in hotter climates.

April 1, 2011	#1
MrTudball Tomatovillian™ Join Date: May 2009 Location: Nebraska Posts: 48	How hot is to hot for seedlings Tried to find this thru search but came up empty, I'm sure the answer is in plain site but I couldn't find one. I put my seedlings out in my greenhouse for the first time this year. Went out today, outside temp was 52 and inside temp was 90. I can vent if need be, but at what temp does it start to effect the seedlings? Last edited by MrTudball; April 1, 2011 at 06:56 PM.

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April 1, 2011	#2
maf Tomatovillian™ Join Date: Jun 2010 Location: England Posts: 512	Not sure on what temperature will affect seedlings, but if your greenhouse is getting to 90°F it needs venting, at least during the 10 till 3 time of day when most sun is on it. You are inviting fungal problems without sufficient airflow, due to the increased humidity. I vent greenhouses any time they get over about 70.

April 1, 2011	#3
ireilly Tomatovillian™ Join Date: May 2010 Location: Dallas Posts: 344	I am not contradicting maf's advice but I can tell you that I have had seedlings starting as late as July-August here and it was over 100 degrees at the time. But - when it gets that hot not much really grows. Even the watermelon and okra kind of just hold their own at those temperatures. But it does not kill the tomato seedlings. What does kill them is the intense sun drying them out and they flop over from low vascular pressure - if you don't keep them watered. I was watering every day then, sometimes more than once. So - not ideal, but they can survive. Thrive - not really. Walter

April 2, 2011	#5
b54red Tomatovillian™ Join Date: Sep 2009 Location: Alabama Posts: 7,068	As long as the plants are adequately watered they can take some really high temps; but maf is right about the high humidity causing diseases to flourish. Another problem with the higher temps on small tomato seedlings is they can become too leggy.

April 2, 2011	#6
travis Tomatovillian™ Join Date: Jan 2006 Location: Evansville, IN Posts: 2,984	Cool, even temperatures promote more stocky seedlings, while high temps will cause the seedlings to stretch out and get leggy when they're still in tight quarters of plug trays. In addition to shorter internode spacing, cool temps between 55 - 65 degrees F at the first through second true leaf stage also promotes earlier, fuller fruit set. But it's not always easy to maintain the milder temperatures in greenhouse conditions unless you have vents, fans and sometime chiller units in hotter climates.