Maybe your greenhouse is in the shade, our unheated greenhouse on cool Camano Island has been above 80 many times this spring - we have started using the ventilation fan to keep the plants from cooking.

Last time I grew tomato plants ('Sunglo', on Camano Island) they blighted off in August. I definitely think growing these under some kind of cover, even a clear roof with open sides is the way to go here.

A friend uses coverings to grow melons, tomatoes etc. in raised beds north of Seattle. There is also fencing all around and reflected heat from the front of his house.

Can't be bothered with protection nor much fussing :-) The older I get, the simpler I want things to be. Only put out my tomatoes this past week so it's sink or swim! I do tend to grow varieties that work well in our short, cool season, grow 'em in big black nursery containers to maximize soil warmth and site them on my south facing deck so they receive reflected heat from the side of the house.

I am doing a cherry tomato grow-off this year - Sungold, Isis Candy, Red Lightning and Italian Ice. Sungold is my absolute favorite for flavor but Isis Candy is supposed to give it a run for its money. The great thing about cherry tomatoes is that a bunch of green ones at the end of the season just means a fresh batch of pickled green tomatoes for Bloody Marys!!

I meant the greenhouse kept overnight temperatures above 50 degrees. It gets warm during the day especially on bright sunny days, so I open more vents or even the door.

I haven't put any tomatoes in there yet because it simply has been too cold at night.

We have a fan on all the time with slightly open vents and a no freeze boat heater. I have jugs of water on the brick floor and keep a jug on a black shelf that warms in the sun.

I mostly use the GH like a cold frame since it's only 6x8 and plastic over cedar framing. It works great for overwintering dormant and starting up again in spring tender perennials (fuchsia, begonia, geranium, canna, dahlia, etc.), hardy seed starting, cuttings, & hardening off, but it's also nice for growing greens in summer because it is part shade of big leaf maples and fir trees in my backyard. It's easier to keep the humidity up for the fuchsias in spring and the greens in the summer. It's also a great privacy screen for the patio.

The GH isn't a necessity, but a luxury type cold frame so I don't have to bend over to tend plants.

I started seeds indoors end of Feb. and set them out under SW eaves in wall o'waters about 3 weeks ago (black plastic pots). Throw a thermal blanket overnight when it is too nippy. So far they look great with flowers starting and have stout stalks. They are Brandywine and Sungold. My Principe Borghese only got started a couple weeks ago. They will all have to live in pots (up to 5 gallons each).

Gardengal I would love to hear what you think of Isis Candy. By the time I got to the Tilth sale, they were gone. Cherries seem like such a good bet here. I am exploring other disease-resistant OP tasty beefsteak alternatives to Brandywine.

I put out some tomato plants in mid-April, as I was tempted by our beautiful weekends. I bought this red plastic that Ciscoe Morris supposedly recommends. It comes in a 20 foot length (I think) and you pull it over the tomato cage and twist tie the top closed. Before I found this red film, I simply used the plastic dry cleaner bags (as recommended by Ed Hume) and those worked well in insulating too. But the hard thing is remembering to take them off before the temps get too hot or the plants will fry.

Nights in the 40s still being forecast.

Some ideas that are working to help keep the tomatoes happy while we wait for those overnight lows to be 50 or higher....

On sunny days the tomatoes go outside as soon as temps are over 50 degrees as measured on my shaded porch. I have my garden cart ready to load tomatoes and then pull them to the sunshine and use the cart to bring back to the front door in the evening. If I need to use the cart during the day I set the totes on cardboard on the ground -- checking for slugs 1st before putting them down.

On cool cloudy mornings I've put the tomatoes and cucumbers out in my car parked in the sunshine. They get brighter light than in the house and the car warms up faster than the outside air.

Yesterday early evening I put them back in the car & they stayed there overnight. The low was 40 here last night, so I hope they did okay in the car.

Pots are inside clear plastic totes (shoeboxes, sweater, underbed storage, etc), so are super easy to lift & move around without making a mess in my home or car. Also ideal for watering from the bottom as long as you empty what doesn't soak up in an hour or so.

Keeping these warm weather plants happy until planting outside...

My tomatoes are long time ago in unheated GH.
I just keep there jars with water that keep temp warmer during nights. Tomatoes are flowering already.

I've got tomatoes under a hoop house/cloche and they're flowering. Not sure if they'll set fruit in the cool weather we have now, but the plants look very healthy. I think that even if they don't manage to set fruit, having large robust plants in place by the time the weather improves does help a good deal in the long run, although as noted it does involve a bit of fuss...

Hope this helps someone new to planting tomatoes. I found out what works here by trial and error. Earlier isn't better for us here.

We're at 500' in a clearing in the woods that gets about 2x the rain as measured at SeaTac, so well over 60 inches a year. Our microclimate is cool due to tall trees and not a prime tomato growing location because of the moving shade throughout the day. However, we do get tomatoes and hopefully enough to can them this year.

We're growing tomatoes purchased locally quite inexpensively. I was very picky in my selection of healthy plants and made several phone calls & trips to Kent McLendons in April to get plants delivered that day only & none that spent the night outside at the store. I didn't want any stressed plants. The 2 gallon pots were from the Earthworks fuchsia greenhouse for $2. I wanted an assortment of maturity to spread out the harvest a bit.

I bought $ .99 3 plant pony packs, $.99 4" pot, & $2 gallons = Early Girl, Early Girl improved, Early Girl Bush, Roma, La Roma, Lemon Boy, Sun Sugar, Super Fantastic, Oregon Spring. I put them in clear plastic totes to haul in & out of the house as weather conditions allowed. I bottom watered with warm water only each morning, but didn't let them sit in water for more than 1/2 day soaking up. I fed them weekly with a diluted manure tea made from a bucket of alpaca manure I kept outside. They stayed dark green and didn't get too leggy in the larger pots. The 3 to a pack pots were a bit rootbound when planting out & probably would have benefited from potting into individual pots. I planted one Lemon Boy into a gallon pot using Whitney Farms premium potting soil for our daughter's place at the same time I put them rest out in the garden. Inside a cold frame is growing so well you wouldn't have guessed it was in a small pot a week ago. I've watered it once and it's plenty moist yet.

I have more tomatoes started from seed Stupice & Amish Paste as an experiment mostly. I planted them in cups in plastic totes in a cold frame outside. Next year I'll start sooner, but we'll see how these small vigorous starts perform as compared to the purchased hothouse tomatoes.

We planted last week in our sunniest location at the top of a slight slope in our garden area along our driveway. This is a permanent mounded bed that was covered with leaves & grass clippings in the fall and horse manure + bedding in late winter. Soil was turned over in April, additional rocks removed, and raked to prepare for planting and warm up without the sheet mulch. Since our spot is on a slight slope, so we use old straw pulled off in sheets as well as other mulch to keep soil in place and keeps us cleaner when working in the garden.

This was our planting routine for starts well hardened off once the soil temperature was consistently 60 deg +

-soaker hoses down middle of bed held in place with long pins made from wire hangers (2 per hanger)
-red plastic perforated mulch in 3x3 sheets (new this year & on soil for a week before planting)
cages, overlapped slightly to cover the 28' long row & held in place by the cages + large rocks

tomatoes still in pots spread out in small groups to spend the night in their approximate location (covered with large upside down clear totes, plus warm water in milk jugs)
-clipped off leaves on bottom 2/3 of plant except for the gallon pot sized plants where we left the branching & upper 1/2 of so
(some years I go ahead & snip the flowers off, but this year on the larger plants left them to see if they drop blossoms or set fruit)
-2 tomatoes trenched on either side toward a corner with a cup of amendments in the planting hole (didn't plant straight down, but mostly at a 30 - 45 degree angle (holes dug with trowel & hand as soil was loose)

mixed in the bucket for each tomato
1/2 cup complete organic fertilizer (Dr. Earth brand)
handful bonemeal
handful calcium carbonate lime
handful crushed eggshells from our chickens

watered with warm water
covered with bottomless plastic milk jug (no lid either)
bottom cut off of clear plastic bag & slipped over cage (held in place with a strip of panty hose)
jugs of warm water set around plant inside cage or just outside plastic to help hold it down flat

2nd day after planting
watered again with warm water
adjusted plastic as needed to keep the tops of the milk jugs from being covered by the outer plastic

1 week after planting
growing & starting to touch the top of the milk jugs
the largest ones were staked to t-posts in the row, surrounded by milk jugs of warm water, but weren't covered with plastic because they were too large --

-- Early Girl had fruit on one cluster & another cluster of blooms at planting, now fruit is cherry size tomato & there 2 clusters of flowers & has grown at least 4" to attach it again to the stake. Pictures would be more complete, but it seems that there is more branching out as well as compared to when it was in the pot.
-- Roma has 3 flower clusters when it had 1 opening & another just showing

Soil is still moist - no additonal watering necessary. If we don't have an inch of rain I will run the soaker hoses, but want to wait as long as possible, so no cold water gets to plants. Usually, about 1x a month now while it's still cool. When temps are over 70 for several days I will increase to about 1x a week then gradually lower to 2x a month. I don't water as much once fruit is set & ripening -- just enough to prevent wilting. Too much water makes watery tomatoes here.

Continued care:
As soon as the plants are touching the jugs I will remove them, but keep the outer plastic.
As soon as the the plants touch the sides of the outer plastic I will take them off.
When the filled jugs of water get in the way of the growing plant I'll remove.
I might make my lazy compost tea (a scoop of compost in a watering can for a few days) to give them some liquid feed, but no additional fertilizer is planned.

To ripen:
No watering after August 15 unless plants are wilting. By then the root systems are deep & find the water they need.
Snip tops of plants around Labor Day. If at least 5 trusses of fruit will sometimes snip in mid-August for plants I want vine ripened fruit more than I want a large total harvest.
Wait to pick that 1st tomato one on each plant until it's very ripe -- encourages more to ripen on the plant. At least in my own mind it does.

Clean up:
remove all the tomato foliage and fruit at the end of the season & cover the soil again with a sheet mulch of compost ingredients + lime (calcium carbonate 3 years in a row, then dolomite lime the next year)
Sometimes I also cover the soil with black plastic or burlap.
After Halloween season I gather straw bales & store outside all winter near or over part of the tomato beds for use as mulch the next season. That way I can pull off thick sheets & they're no longer slippery to walk on plus more absorbent of moisture.

Gardengal, in case you see this (and I know you posted a month ago, but perhaps you will anyway!), I grew both Sungold and Isis last year. When they eventually fruited, I tried some from each plant, and happily decided Sungold was still my favorite. Then I went to look at my chart of which tomato was planted where -- and it turned out I'd been enjoying the Isis much more than the Sungold all along!