lows in the lower 40s

Yes, cover them to prevent damage. Lots of discussions here about this and the general guideline is cover when temps fall below 50-55. Would they be ok without cover? Possibly. But it's a risk to be avoided when possible.

Also when are you supposed to remove the black plastic mulch- temperature wise and month? Can I add straw mulch on top of the black plastic at this time or do I need to remove the plastic mulch completely before I add the straw?

In your zone you can probably leave it in place and just cover it with a thick layer of straw. It works fine for me that way even in my zone but I am using landscape fabric with air holes in it, not black plastic.

But in southern zones where the heat is steady and intense many find they have to remove it to avoid heat build up in the soil that happens even with thick mulch on top.

Dave

temps in the 40s are not going to harm your tomatos unless it is a constant temp in the lower 40s for days on end. If the temps dip into the mid 30's then you should cover them to shield them from the wind.

If you have nice sunny days you really don't have much to worry about

Is the lower 40s forecast for the standard temp or just nightly temps?

This post was edited by Erich_k on Wed, May 22, 13 at 11:20

Just to be safe I'm going to throw some fleece on them and leave it on for a few days it lets in 85% sunlight. The forecast has lows at night 41-45d for the next 4 days with highs of lower 60s.

Tomato plants are susceptible to chilling injury at temperatures between 32 and 42 F. Chilling can cause stunted growth, wilting, surface pitting or necrosis of foliage, and increased susceptibility to disease. Low soil temperatures also stunt plant growth and prevent root development. Temperatures below 50 F during flowering can interfere with pollination and result in catfacing of fruit.

So, I say go with Dave's recommendation and cover the plants if you can.

Weird spring we're having.

Betsy

FWIW, unless there's potential frost in the forecast, I never cover them. We're supposed to have lows in the low 40's coming up this weekend for 3 days or so. As long as they don't get nipped by frost they always have survived and done fine, and I've not noticed any stunting or anything. Also, the night's are very short this time of year.

One thing to keep in mind when making your decision is the difference between the air temp at the standard reading level of 5-6 feet and the air temp at ground level. Ground level air temps can be as much as 10 degrees colder depending on humidity and wind.

Obviously there is a great deal of difference in the effort required to cover 50 or more plants than to cover 10-12 plants or less just as there are many variables than can determine the type and degree of damage done. Some prefer to take their chances rather than cover no matter how few plants they have. That is their choice, their risk to take. But to claim there is no risk at all isn't accurate and there is ample research available to support that claim.

Dave

Just for the record, I never said that there was no risk or made any absolute claims. Only my experience of living in Z4 or Z5 through many springtimes. In my experience, with only ground truth to go on, have never seen any ill effects of a few cool (without frost) nights on a tomato plant. In my experience they are actually very hearty as long as ice doesn't come in contact with them. Even though I have a degree in Meteorology, I still consider myself a student of it. And Dave, I've read alot of your posts, and for the record, you definitely know more than me about gardening, and probably always will. These days I seem to be forgetting at a faster rate than I'm learning :-)

Yeah wasn't referring to your comments specifically Ed. Sorry I didn't make that clear.

temps in the 40s are not going to harm your tomatos unless it is a constant temp in the lower 40s for days on end. If the temps dip into the mid 30's then you should cover them to shield them from the wind. If you have nice sunny days you really don't have much to worry about

Although I do think you have some luck on your side and that the damage that might be done may not always be obvious, my comments were in response to that quoted claim. Check out the article linked below for some additional info.

I have over 100 plants so covering all of them is not an option for me anyway. So I do selective variety covering. And I sure can see the difference in my plants that were protected when a surprise 40 degree night comes along and the ones that weren't. Stunted? Not in the usual sense of the word but slower growth, less fruit set and production.

Just something to consider. Ultimately the sun will still come up in the morning either way. :-)

Dave

Here is a link that might be useful: Cool Nightlife Bad for Tomatoes

Dave (digdirt) - I was looking at that very same article this morning (see the Hardening Off thread). I was wondering since they said cold temps disrupted the circadian rhythm of the plants, but mentioned as example temp dropping at 10 pm and taking 10 hours to come back over 50, have you seen any ill effects from dropping more briefly? Low is usually around 5am, and temps climb right back up after sunrise.

So will say 3-4 hours each night (let's say a few nights in a row) of mid-40's hurt production?

Dave (OP) Temps are crazy around here, near 90 yesterday, 70s today but high will only be 55 on Sunday with low possibly getting down to 39, then by Tuesday will be low 70s and Thurs low 80s again. At least that's what they're predicting now - seems like the forecast changes every couple of hours.

This post was edited by ajsmama on Wed, May 22, 13 at 21:28

Related question here; after daytime temps of 80f in Montreal, I planted 12 heirloom tomatoes. Unfortunately a few days later, nightime temps went into the 30s.

I covered them with an agribon-19 floating row cover, but some plants have black tips on the leaves, and the flowers died. Others look OK, with healthy flowers.

Should I give up on the damaged ones now and replace them, or is it possible for them to bounce back? Unfortunately my garden center only has beefsteak type tomatoes, so I'm hoping that they'll produce, even at reduced capacity...

With reference to the plastic mulch, cablestarman, I can't think of any reason to remove it before the end of the season. The straw would be an option only to provide a mat for fruit if you were not going to use any plant support. Otherwise the straw will be a waste of time and money. But you only gave no info about the dimentions of the plastic mulch, the watering methods or the plant support method.
Cvinson, you have just experienced a setback but by no means should you give up on those plants until they kick-the-bucket. Likely the Agribon was a little light for the freezing temperatures and if the bulk of the plant looks healthy you will get continued growth and dozens of more flowers to replace those lost.

Ok. Here is my story:
shortly after I planted my tomatoes( when it was hi=+75f, Lo=50+) the weather turned around and got cold. For the last two weeks our Hi have been 56 to 62F and night lows at 42 to 46F. Despit of all that some of my tomatoe have growm more than 10" in height. So what happened?

NOT ALL LOW 40s ARE THE SAME:

When they say " tonights low will be 43F", it does not tell me the whole story. Suppose the day before's high was 63F and the following day's high will be 65F. SO, what kind of pattern we will have between those two highs ? HOW LONG will that 43F (43 to 46 ) will hang around ??? In most cases it will me less than couple of hours.

Another important issue is : How your garden is situated against te winds" How the winds will blow ? A 43F withoul wind is much better than 46F and windy.

Plants are just like us, humans. They feel the cold more (by losing mor heat) when it is windy and dry. Therefore, often inverting a container, bucket etc on a plant at cool nite can keep it warmer(by not losing heat too fast)

Ed:

Just like weather forecasting, gardening can be very humbling. No matter how long you have been at it situations will arise that you haven't encountered or you just flat make mistakes. I think that is the most appealing thing about both. The average frost free date here is around May 10. Afraid of a couple of weeks of wet weather I decided to plant out ten plants ahead of the rain about 5 days earlier than that. We had a low of 34 a few nights later and although I had buckets on them the plants turned a bit yellow. I don't think it helped that a few days after that we were at 88 degrees with 30 mph winds. Anyway the plants that I put out ten days later stayed green and passed the other ones up. They all look good now and I don't know if there was really any lasting damage done. Bad call on my part about what the weather was going to do, as we did get 2 inches of rain but it dried up fairly quickly. We do have temps forecast to get around 40 in a few nights. I probably won't cover the plants and I have a few more to put out after that so I guess I will have a pretty good test plot on what effects these cold snaps might have.

seysonn: Agreed. The big concern for early tomatoes here is the humidity in addition to temps.

Never realized WA is in same HZ as TX. I may have known that once upon a time but as Ed says, "These days I seem to be forgetting at a faster rate than I'm learning :-)"

We had a heavy frost/light freeze here on May 14th. All my plants were still in WOWs except one. So I turned over a garbage can on the 'one.' Didn't realize that the can had a crack in it, and the frost killed about half the plant. It's definitely behind the others now but recovering strong, and I'm expecting that in a month or so I won't be able to tell the difference. A lovely Memorial Day weekend on tap for here.......cold, rainy, and windy.

Hey, it is forecast to be below 50 here tonight. For this time of year, where I live, that is pretty unusual.

MksinSA,'
" Never realized WA is in same HZ as TX"

zone numbers don't mean much in terms of temperatures. Zone 8 means that there is roughly 8 months of growing season; from last spring frost to first fall/winter frost. probably our temperatures during growing season 15F cooler than zone 8 down south.

"zone numbers don't mean much in terms of temperatures. "

Actually, that's exactly what zone numbers mean. :) Hardiness Zones don't tell you the length of the growing season; they tell you the average minimum temperature for a given location. Your Zone 8 means it gets down to an average of 10-20 degrees in the winter. Austin, TX gets down the same average lows, so your areas are both listed as Zone 8.

But that doesn't mean your last average frost dates are the same, or that your average temperatures through the summer are the same, or that your growing season is the same length. All Zone 8's (or Zone 5's in my case) are not the same, so just because someone in TX has planted their tomatoes outside doesn't mean you're behind if you haven't.

In general, Zones are more useful information for perennials -- will they survive the winter low temperatures -- than for annuals. That's why you see perennials marked with "Z5-8" or whatever, but you don't see vegetables identified that way. An area's average last & first frost days are more useful information for vegetable growing.

The attached link explains it well, bringing in Heat Zones and how Washington significantly differs from Texas, even though they both are in Hardiness Zone 8.

Kathy

Here is a link that might be useful: Washington State Extension - Hardiness Zones

cvinson, I live in Montreal, and the hot weather got me overly optimistic and I started hardening off the seedlings. Needless to say, they aren't planted yet. Too cold and rainy. Where r u located? Cause there are still lots of varieties at some of the nurseries and the markets.
Sharon

Actually, that's exactly what zone numbers mean. :) Hardiness Zones don't tell you the length of the growing season; they tell you the average minimum temperature for a given location. Your Zone 8 means it gets down to an average of 10-20 degrees in the winter. Austin, TX gets down the same average lows, so your areas are both listed as Zone 8.
Kathy

I did not say anything about "AVERAGE MINIMUM TEMPERATURES" that doe not concern me. But what I said was, to the effect, that zone numbers, in terms of growing season temperatures, don't mean mud. And I mentioned and example comparison, zone 8 in PNW and down south, GAAnd I am pretty sure that zone numbers closely corelate to the length of growing season in months. For example: a zone 11 has 11 months of frost free period. It does not tell me anything about the growing season temperature.

No, a Zone 11 region has frost free, year round growing. Zone 10's lowest temps are in the 30s-40s, very very rarely freezing along the coast especially, and they also have 12 months of growing. The fact that the months of growing season sometimes correlates with the arbitrary numbering system of the USDA (as it does here, in Zone 8) does not mean it works all the time.

Crap, we have a frost advisory for tonight :-/

Us too. Just got in from covering strawberries (again), after dinner I think I'll cover my spinach transplants (and the kale in the same bed). Unfortunately, blueberries and raspberries (in bud) are on their own since we're having gusty winds and I have no way to secure any coverings.