The 90 degree myth

[ronsmith100]

Over the last two years I have run across many tomato gardeners who have said, "you cannot set fruit when it's over 90"... and right behind them someone says "oh yes you can".
Lump me into OYYC group. We're over 5000 ft elevation and have been over 90 every day for more than a month and the 'matoes are still setting.

But this got me to thinking about climate and things and I was wondering if maybe those people who are not successful in hot temps maybe live in a higher humidity.
Could it be that the humid hot air makes pollination more difficult?

For example it is hot today (heading to 90 plus) but humidity is very low.. could it be that in high humidity the pollen sticks to the thick air on micro droplets and is carried away?

Just curious

Anyway I have a 20% uV net over them because the radiant heat of the sun through our thin atmosphere can burn them badly. But so far heat hasn't slowed anything.

[carolyn137]

Just a couple of comments.

First, many varieties, not all, are susceptible to sustained temps ranging from over 85 F and that's why professional hybridizers are always trying to breed more heat tolerant varieties. Pollen is protein and is actually denatured, aka destroyed at high sustained temps.

And yes, humidity plays a big part in the equation. High sustained humidity or even when rain is a consistent common event clumps the pollen so that it's much less effective.

And those in the SE who have to deal with both heat and humidity have a real problem. A big Problem, which is why they try to start seeds around Jan 1st and get plants out by early March so that fruit set can occur befire the heat starts and the plants shut down, and they do shut down.

But most of my tomato friends in the SW and CA where high heat alone can be a problem, also start plants early to escape the summer heat.

[KsMama11]

We are having temps around 100, & none of my plants are changing colors except the cherries. Really worried about my Brandywine plants, one is as tall as me, covered in huge fruit. Will it ripen, or should I pick the fruit green? Forecast is for a 100 degree temps all week long.

[kath]

Originally Posted by KsMama11

We are having temps around 100, & none of my plants are changing colors except the cherries. Really worried about my Brandywine plants, one is as tall as me, covered in huge fruit. Will it ripen, or should I pick the fruit green? Forecast is for a 100 degree temps all week long.

The extreme heat and humidity causes problems with the pollination of the plant but not for ripening fruits.

[Stepheninky]

Originally Posted by KsMama11

We are having temps around 100, & none of my plants are changing colors except the cherries. Really worried about my Brandywine plants, one is as tall as me, covered in huge fruit. Will it ripen, or should I pick the fruit green? Forecast is for a 100 degree temps all week long.

They will ripen, It does seem to take forever but in the heat I notice once they blush it is a fairly quick process like 2-3 days. I usually pick mine at blush or a day after and let them ripen inside due to birds and squirrels.

[KsMama11]

Originally Posted by Stepheninky

They will ripen, It does seem to take forever but in the heat I notice once they blush it is a fairly quick process like 2-3 days. I usually pick mine at blush or a day after and let them ripen inside due to birds and squirrels.

What exactly is this "blush"?

[Stepheninky]

Originally Posted by ronsmith100

Over the last two years I have run across many tomato gardeners who have said, "you cannot set fruit when it's over 90"... and right behind them someone says "oh yes you can".
Lump me into OYYC group. We're over 5000 ft elevation and have been over 90 every day for more than a month and the 'matoes are still setting.

But this got me to thinking about climate and things and I was wondering if maybe those people who are not successful in hot temps maybe live in a higher humidity.
Could it be that the humid hot air makes pollination more difficult?

For example it is hot today (heading to 90 plus) but humidity is very low.. could it be that in high humidity the pollen sticks to the thick air on micro droplets and is carried away?

Just curious

Anyway I have a 20% uV net over them because the radiant heat of the sun through our thin atmosphere can burn them badly. But so far heat hasn't slowed anything.

I can get fruit to set but its not in the numbers it would be later or earlier in the year before the heat sets in. Yes plants do seem to slow down and somke will just stop. What I do is try to get the plants though it best I can and in Sept they will start setting better again.

At your elevation you probably have cooler nights. We have 90 - 100's but night time temps do not really drop much so that might also be a factor. Last Tuesday it was still 89 at 10:00 pm.

Cooler nights might give the plants a window to make viable pollen that if used before daytime temps climb could set fruits.

Humidity is also ridiculous, Saw a post on here where someone complained about 50% humidity. We have been having 78 -80 % humidity, so yea it makes a huge difference

[Stepheninky]

Originally Posted by KsMama11

What exactly is this "blush"?

On a tomato blush means it starts to change color. Once they start to change color they will finish ripening on or off the plant.

[Dewayne mater]

I tend to agree that night time temps and humidity are key factors in fruit set. Hitting 90 (or up to 94 with some types I'm told) is one thing, sustaining temps over that daily and night temps that "dip" to 85, and tomato time is over. That said, you might still get a few stragglers that some how, some way set.

I the last 2 weeks, our lowest daily high was 100 and at night it barely cools to the mid 80s. Humidity is enough to make it uncomfortable when the temp cools overnight. Somehow, through that 2 cowlick brandywines have managed to set 2 fruit each and one Earl's faux set 1 as well. So, I wouldn't say it is a 100% certainty that high heat dooms tomato setting, but, the kind of success you may get it so few and far between that it isn't really worth it. I should also point out that cherry types, for me sun gold especially and black cherry to a lesser extent, are still setting fruit, just far less successfully than before someone left the doors to hell open.

P.S. i also use 50% shade cloth and I'm convinced that helps, and I grow in earthtainers. I've definitely experienced some increase growth and increases in blossoms when I put liquid fertilizers in the water reservoir...but that is the topic for another thread. Good luck.

[Sunsi]

ronsmith100

We're over 5000 ft elevation and have been over 90 every day for more than a month and the 'matoes are still setting.

So you're saying you have a good view AND tomatoes, too!?! sheeesh!

Happy gardening!

[creister]

I imagine in s. Utah your night time temps are in the 60's? I lived in Ely, NV for a year, and in the summer, we were always in the 60's at night even when temps were in the 90's.

I think night time cooling, which for cattle is below 70 is very important as well. I remember that figuring AUM's for cow/calf always had to account if night time cooling was happening, and that was temps below 70. AUM is how much food said cow/calf needed to gain, so nighttime temps above 70, needed more AUMs. Maybe mother tomato plants and fruits need more chow if it's too hot at night also. Hope this makes sense.

[Keiththibodeaux]

The local advice here has always been that tomatoes quit fruiting when the nights no longer fall below 80s degrees. I have never heard daytime highs being mentioned till now.

[Gobig_or_Gohome_toms]

Well the next few days here should be interesting humid and highs of 95+ with heat index of 105+ my terhune is now loaded with blosoms 6-7 trusses flowering I hope a few will set.

Craig

[travis]

Originally Posted by Keiththibodeaux

The local advice here has always been that tomatoes quit fruiting when the nights no longer fall below 80s degrees. I have never heard daytime highs being mentioned till now.

I've heard daytime temps mentioned as a factor, but Keith is right on this one, it's the nightime temp that's more critical. And at 5,000 feet, your 90 degree climate is a whole different planet from the Old Man River and back bayou 90 degree world.

[KsMama11]

They are calling for LOWS of 82 this week... sounds miserable to me.