Temps above freezing but colder than plants like

[gorbelly]

I'm finding a lot of conflicting information regarding the damage that cold temps that are still above frost can do to plants.

Some people seem to think that temperatures that are colder than what plants like will permanently damage/stunt them, even if they do not suffer frost damage, while others seem to think that it will just slow their growth while they are exposed to the cold temperatures but not affect their later growth when the weather warms up.

I realize that it probably also depends on which specific plants we're talking about (for example, some basil varieties will get black leaves with temps in the 40s), but I was just wondering whether there is a general principle here. For example, during spring, when temps can get down into the 40s at night but be well into the 60s or even 70s during the day--is being exposed to a few hours of temps in the low 40s permanently damaging for young plants?

[rhines81]

I recently did some research on this and the first thing to identify is what the information is drawn on. Many sites discuss first frost (for late summer/fall planting) and others discuss last frost (for spring planting). If you can separate the two, which is sometimes difficult, then your information will be more consistent. If you run across information and it is unclear whether they are talking about in terms of Spring or Fall planting then just move along to a better source.
Use heavy mulch or straw for Spring planting.

[gorbelly]

Thanks, but I'm not so much concerned with actual frost/freezing temperatures as the effects on plants of cold-but-not-freezing temperatures.

[rhines81]

Impossible to answer as it depends on what you are planting and at what growing stage the plant is at. If it is a frost tolerant or semi-frost tolerant plant, then you could be fine with a night of 28-36F temperatures with maybe only slightly retarded growth and quick recovery.
Peas for instance may be able to stand several days at 20F while the seed is germinating, 28F might kill a seedling, 32F might devastate any flowers even for a short time but the plant itself would recover.
You'll have to research each plant.

[gorbelly]

Yes, but as I keep trying to explain, I'm NOT talking about freezing temps. I'm talking about above-freezing temperatures that are colder than is listed as optimal for plants. Obviously, with any young plants, even cold-hardy ones, avoiding exposure to actual freezing or below is important. I'm talking about exposing, for example, vegetable seedlings to 45 degree temps, etc.

[rhines81]

A few hours out their comfort zone will not really hurt any plant (again mulch is important). Overnight, 12 hours or so with gradual warming back into the zone and repeated cycling of this is not good ... this is where you need to be more specific: as to what "Vegetable Plant(s)" you are speaking of.

For example--- 45F for 12 hours with repeated cycling over a several days:
Okra -- a dead duck, never will recover.
Peppers / Tomatoes -- maybe some shock, slight wilting.
Spinach / Cabbage -- will be fine and enjoy the refreshing coolness.

[Cole_Robbie]

I have a few thousand plants right now in an unheated greenhouse that dips down into the mid 30's. I think I know the answer to your question, but it's all just my guess.

What happens with a container plant that gets cold like mine do is that you start to spin the bacterial wheel of fortune. Fertilizer in the media that doesn't get used by the plants, especially when it gets cold, can start to grow anaerobic bacteria like pythium. Plants show nutrient deficiencies, turn yellow and purple, and just look sickly, like this: http://i.imgur.com/EIYzIZC.jpg

Having said that, my overall greenhouse looks like this: http://i.imgur.com/UgmXEHT.jpg

It's going to get down to 37 tonight, and I didn't even close the door. If I went through and culled everything right now that didn't look perfect, I might lose 10-20%. So it's worth it for me, because that is a lot cheaper than paying for heat.

However, let's say a person only has a few plants, and each one is very important to them. In that case, no one should do what I do. Don't let your plants get cold if you can't afford to lose any.

[BigVanVader]

If I remember correctly a little cold is good for them, making them stronger, but beyond a few low 40's nights in a row I have seen damage and usually some will not recover. If I lose a handful its ok b/c that is just natural selection and I don't want to plant cold sensitive plants in case of a late cold spell or freeze.

[sjamesNorway]

I use "The Cold Treatment" on my seedlings, and it works well.

http://www.tomatoville.com/showthrea...cold+treatment

Then again, there's this paper from the U. of Colorado extension, with a passage about temperatures.

http://www.ext.colostate.edu/mg/Gardennotes/717.html

There would seem to be a very fine line between what's beneficial, and what's detrimental.

Steve

[bower]

For sure it depends on the vegetable you're talking about, because their tolerance of cold is very different.
Onions, leeks, kale, broccoli, cabbage, turnips, lettuce, peas, carrots... are very tolerant of cold even as seedlings. (On the other hand, peas that are not sprouted can rot and die if the soil is cold and wet.)
Tomatoes, beans, squash and basil are a lot more sensitive to cold, even above freezing.
Beans squash and basil, it's just as ColeRobbie said they get sick and rot.
We can only put beans and squash outside after midsummer or in July here, where it's cool, and no one would even think of trying to grow a crop of basil outdoors. Ever. Beans are also pretty challenging (except for favas).
Tomatoes, may not show any damage but I have seen, with side by side of the same variety, that too harsh exposure to cold resulted in later fruiting (for the varieties I compared). Some other varieties did really poorly all season and could possibly have been a permanent setback due to the harsh cold treatment. And some other varieties may be just fine in spite of it. Lots of variation in the tolerance, even after the "cold treatment" for seedlings, which is supposed to activate cold tolerance gene expression in tomatoes.

[ChiliPeppa]

My okra seedlings got left out at night by unintentionally twice and though they got droopy they sprang back just fine. Temps were in the 40s and down to 37-39.

[twillis2252]

Originally Posted by ChiliPeppa

My okra seedlings got left out at night by unintentionally twice and though they got droopy they sprang back just fine. Temps were in the 40s and down to 37-39.

Had the same issue late last Summer with mature okra. Temps upper 30's at night and 60's daytime. Okra still produced until a frost took them out...