Hi frost is basicaly frozen dew the temperature has to get below freezing for it to form however it won't all melt if the temp creeps back up to 33* if the temp is below freezing and the dew point temp = the air temperature then frost will form. also tomatoes don't like cool temps so I'd wait a week or two until it's warmed up. Also make sure your passed your avg last frost date for your area.

Here in the Central Basin in TN, zone 6b/7 the avg last frost date is around April 15.

google . They have 'year at a glance' and a 'daily/monthly' historical weather data base including high/low temps for most mid to large cities.

I see you are in zone 8, but you don't say where you are located. I'm also zone 8 and our avg last frost date is March 17th. It has been beautiful here also, but the temperature can drop quickly. To give my plants more light before I can transplant in the garden, I take them out side for a few hours (after hardening them off) and then bring them back inside before the sun sets. You can even leave them out all day if you check the weather report and it is not supposed to be at or below 32. I wouldn't advise planting anything until closer to your last frost date. If you have WOW you might be able to plant out as much as 2 weeks earlier, but to be honest I've never used them so I can't say for sure. Good luck!

I'm located just south of Austin. I've checked and the last expected frost date is March 7-15th. However, I'm putting more stock in the 10-day weather forecast to determine a good time to plant.

Right now, as soon as I can prep the beds, I plan on putting at least three in the ground. I have three WOW's and I'm anxious to see how well they work. Any more than the three will have to get protected by half milk jugs. I would have planted sooner with the WOW's, but getting everything set up is difficult due to a child with the sniffles and wife who needs inside housework done :-). The reason I'm asking is I see that the coldest it is going to get over the next 10 days is 41 degrees and was curious if this was too cold for the plants. I plan on having them all out and in the ground by March 7th, but wanted to check the 10-day at that time before committing and wanted to know what was considered too cold for transplants (frost).

32 degrees is when frost will form. Anything higher will not hurt the plants. Happy gardening!

In addition to avoiding frost, some rec soil temps above 50F some even 60. Here are just a few references.

"The safest way is to get a soil thermometer and take the temperature several inches down in the bed you intend to plant. Tomatoes want their roots in soil at least 50 degrees Fahrenheit, but it is better to wait until it warms to 55. When gardeners become impatient and plant early, tomatoes can become dwarfed and stunted, and may not recover."

http://ccmg.ucdavis.edu/CCTimes/Times_08-04-26_tomato-planting.htm

"When it comes to transplanting Tomatoes, you want to ignore your calendar. Outdoor temperature is the most important factor in transplanting Tomatoes; far more Tomato plants are killed by being put into soil that's too cold than from any pest or disease. Both the soil and the air temperatures needs to stay above 55 degrees Fahrenheit, even at night, before your plants are ready for transplant. When in doubt, just keep them inside a bit longer."

http://parktomatoes.com/howtogrowtomatoes.html

"Tomatoes like warm soil and don't tolerate frost, so wait until warm spring days arrive and soil temperatures reach above 60°F to plant."

http://www.organicgardening.com/feature/0,7518,s1-5-16-248,00.html

Frost is 32 but freezing doesn't happen instantly. I put out my first 3 plants with wow on Jan 1 and they're doing great. Now that they have started peeking out over the tops of the wows I gently cover them when it gets really cold. 40s is NO problem at all with wows.

"What is considered 'frost'"
Frost is a covering of ice crystals on a surface. It is produced by the depositing of water vapor onto a surface cooler than 32°F.

"I know that frost is bad for plants."
Yes it is. Frost damages plants because the water inside the cells of a plant freezes and breaks the cells' walls. That part of the plant will die. BTW, black is not a good color when it comes to tomato plants. :)

"At what temperature does "frost" happen?"
See above. You spoke of a temp prediction of 41. Keep in mind that is the ambient surface temperature prediction. Surface temperatures are usually measured 4 to 6 feet above the ground. The coldest air is closest to the ground. So, to present a hypothetical case, let's say the weather person predicted 34 degrees for your area. Let's also say that the prediction was spot on. You still might get frost on your seedlings if the temperature close to the ground (where your seedlings are) was let's say 3 degrees cooler than the "surface" temperature.

"I'm starting to keep my plants outside and even plan on putting a couple in the ground (with WOW's)."
You should be okay with WOWs.

What I always recommend when asked about when to set out tomato (actually any frost tender) plants is:
Determine the average last frost date for your area. Add 2 to 3 weeks to that and you should be fine.

The reason is that the average last frost date is just that an average. So, depending on the year the last frost will be before, on, or AFTER the average last frost date. By waiting a couple of weeks you avoid disasters and you allow the soil to warm which makes it better for the plants anyhow.

Good luck.

Randy

Also pick up your own digital thermometer and have it calibrated.
Our 'official' weather monitoring station is less than two miles from our house. In the parking lot at the fire station and snugged up against a south inside corner of the building.
The 'official' low temp is always at least 2-4 degrees higher than what I record in our yard.

(that would also account for about 99% of recorded global warming LOL)

Corrie

Our weather station is less than a level half mile from us and yet it can also be quite a few degrees colder in our yard than the reported temperature, especially in the early am. (I know this because I've prowled the yard at 3:00 a.m. with a flashlight and a thermometer, looking for microclimates.)

What is Wow

What is Wow

--------------------

t is short for Wall of Water.

A cylindrical /conic plastic with pockets of water.

And my dreaded pedantic comment: NOAA's National Weather Service - Glossary - '' Frost describes the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth's surface and earthbound objects falls below 32°F. As with the term "freeze," this condition is primarily significant during the growing season. If a frost period is sufficiently severe to end the growing season or delay its beginning, it is commonly referred to as a "killing frost." Because frost is primarily an event that occurs as the result of radiational cooling, it frequently occurs with a thermometer level temperature in the mid-30s.''

chellestar83: 32 degrees is when frost will form. Anything higher will not hurt the plants. Happy gardening!

Usually tomato foliage will not die (although do see albert's comment above). However, some people say that too much exposure to low temps (below 50F) not only stunts plants temporarily but also permanently negatively affects plant growth and tomato production. I personally have not observed this to be the case, but I can't be totally sure, as I've never done a side by side grow-out testing this (ideally, one would do this with cuttings from the same plant to make everything identical).

If you're talking generally, different plants have different temps at which they suffer damage, and the cutoff line isn't always freezing temps.

I have grown tomatoes in PNW for 3 season. I have pushed the season by starting as much as 30 days before the traditional plant out. From April 10 to May 15 there had been many nights ( 70% of the time ) night lows in 40s even in 35 to 40F range. My plants ( indets ) ended up growing up to 12 ft tall.Actuall, rarely night lows used to cross 60F on the up side.

Tomatoes are cold hardy plants. They might not grow as fast but they do tolerate cold weather. But if a variety has a DTM of say 70 day down in Alabama it will be like 85 days up in PNW, when planted out real early. .

Sey

I tend to agree that tomatoes seem to do fine once temps warm up. I've always wondered whether the claim that they are permanently stunted stems from the fact that tomatoes set out very early tend to grow very slowly and not end up being particularly early or that much more productive than plants set out during reliably warmer temps. A younger tomato plant put out when temps are nice and warm can quickly catch up to older plants that had been set out much earlier. Plus, there's less loss due to catfacing, etc. Maybe this gives the perhaps erroneous impression that the cold has permanently set back or disadvantaged those plants when what's actually happening is probably that setting plants out extra early just doesn't give that much of an advantage.

I agree, gor, that starting too early in cool weather does not make a lot of difference when it comes to getting ripe tomatoes, UNLESS by luck you get a very nice and warm spring weather. Part of the reason for doing that ( in my case ) was running out of patient and just trying to challenge. There were just a few times that I got ripe tomato in late June and early July, in small quantities.Traditionally tomato is normally harvested starting in early August in the PNW.

Sey

Sey, could be "Very nice Spring weather" or you could have tomatoes in a high tunnel or covered with row cover. I always have ripe tomatoes by early June when other gardeners in my zone are just planting. I find the outcome to be amazing when these technologies are utilized. Frost may form on uncovered plants but covered plants handle the cold very well (to a point).