I can't wait to hear your thoughts
Dave

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

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?

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

Weird spring we're having.

Betsy

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

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

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.

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...

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)

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.

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 :-)"

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.

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

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.