Have you ever had stunted tomato plants before? Life isn't perfect, do you really want to wait over 4 weeks to plant? Look at the forecast and make your decision.

Oh, certainly not 55! I've been starting my own plants for over 30 years, take them outside the minute they are up as long as the temp is above 40 (and bering them in at night, of course). They most certainly aren't stunted.

Look it up!! Tomatoes are very temperature sensitive plants, semi-tropical in origin. Temps that are too cool to their liking result in poor, slowed growth and reduced flowering, especially cool soil temps. As spring soil temperatures are directly influenced by the ambient air temps, if your nighttime temps have not consistently reached an appropriate level, the soil remains cool and the plants will just sulk and do nothing. That's why they sell things like Wall of Waters or protective cloches so one can accelerate the growing season if they wish.

In my location, it is not recommended to plant out tomatoes starts before Mother's Day at the earliest but generally not before June. Planting them earlier does not gain any advantage and will in fact slow their development. btw, hauling starts in and out of doors is not all the same as planting them in the ground! In the UK, almost all tomatoes are grown under glass in greenhouses, as their summers also remain relatively cool with both nighttime and soil temps remaining low.

Thanks! I have cold frames if needed. I read a lot of varying temps but I feel 45 for short periods of time (hours not days) is ok. Soil temps will likely not be below 55 likely higher. I mostly planted sungold which are cool tolerant.

Have to agree there, GG. IME, tomatoes like to be grown fast with no check to growth so even a week or 2 of snivelling in cold will translate into a diminished yield and vigour. Have sown seeds at every time, from late February to the end of April and have found the sweet spot (for me) to be around 14th April, with outdoor transplanting in the second week of June (give or take a week on either side). I want to see consistent night temps of 12C.

I think there is something to be said about the age of the plants. An established and mature plant can handle a cooler spell better than a newly transplanted and not yet established young plant. How well they are hardened off can be a factor too. Well hardened plants can also handle a cooler spell better than plants that are poorly hardened off.

Tomato plants are very picky when it comes to temperatures, and will stop growing below 50 degrees, and with consistent nights below 50 growth will slow or even stunt growth.

They' are also picky on how they will grow in a positive, negative or zero temperature differential between night and day temps, with just a few degree swing around 50 degrees at night.. I'm not guessing, It's proven by science and with a few degrees below 50 degrees you will get slow growth to a stunted plant, and a few degrees over 50 can cause the plant to grow long skinny stems with less xylem vessels. It's best to wait until the night temps are in the Goldilocks zone of 55 to 65 degrees producing the correct amounts of growth hormones. .

Greenhouses can manipulate growth of plants by positive, negative and zero temperature differential. Ever seen dark green stocky little plants at greenhouses with thick fat stems? These plants are grown with No differential between night and day temperatures with even a higher night temp than day temp. These plants should be avoided at all costs when shopping nurseries because they are mutated and bathed with nitrogen to look healthy but will never grow good throughout the season.

Edited, Just read beesneeds comment and he is correct. (he always is). What I wrote is for seedlings still in initial cell development and how temperature effects the production of growth hormones. One link -- https://pmc.ncbi.nlm.nih.gov/articles/PMC7752778/

If you prefer video from a soil scientist, link -- https://www.youtube.com/watch?v=gpDkNQg-4jg

I grew tomatoes commercially. We were told by agronomists, tomatos stop growing at 50 degrees. 50 degrees does not mean they die, they just stop growing.

We used to seed in May, harvest in August/September. Our customer, a local canner retired and the plant shut down, thus we had no customers. I do not think there are any tomato growers left in the area.

California, Sacramento area.

One can always resort to my method....the old light bulb in the tomato box trick ;-)

For those below freezing nights.....plus, a 3 week jump on that 1st tomato doesn't hurt.

Once again, the above advice is useless if planting out in the ground!! A light bulb is not much help trying to raise "below freezing nights" to an acceptable level for toms!!

I personally don't grow tomatoes, but if plants are basically ruined by a 50-55F night wouldn't that mean that most plants are stunted in my area? People plant them late April into mid-May, cover if threat of frost. Lowes has the Bonnie tomatoes and peppers outside uncovered in 40-50F all the time, cover them with a tarp for frost outside on colder nights. Local garden centers have their tomatoes outside on those 40 to 55F degree Spring days. I assume the plants grow for most people. I've always thought tomatoes were idiot proof they were so easy to grow.

I have never had problems with stunted peppers with variable midwest weather. Personally, I would rather plant plants in the ground instead of having them sit around in pots too long, worried about a possible cold night. Obviously, no point in forcing plants out in overall cool temps, but you can always get some cool nights into June, it's life.

Well, I've been using my technique as I said for over 30 years. The minute the plants germinate, they go in and out of the house daily as long as temps are above 40. By the time the weather has settled and they are ready to go in the ground, they are strong plants with thick stems and often have begun flowering. They're not weak, they're certainly not stunted, they're vigorous and they produce magnificently. I've grown dozens of varieties over the years since when I was younger with a larger garden I would try a new variety or two every year just to see if I liked them. For years now I've settled on Jaune Flamee as a favorite--I normally get my first ripe fruit in early July.

I've always been curious about people using the term "stunted" in regards to tomato plants. Extension services will say that a week of night time temperatures below 50-55 degrees F will stunt the plants. Yet people plant out in cooler temps than that every year and the plants will be subjected to it for longer than a week. The plants may not grow in these cool temps but I have never experienced firsthand, nor seen anyone else, have prolonged adverse affects.

So, is the stunting they refer to this brief period of no growth? To me stunted would mean the plants remain permanently small and have poor growth even when temps warm up, but as I said above I've never seen this happen. As long as they aren't killed or severely damaged by frost they do grow when it warms and they do so quickly.

Rodney

It works for me Gardengal to get that extra early tomato at generally a 3 week jump, been doing the light bulb in the box trick going on several years now. Naturally it would be a difficult task commercially, but it allows me to get away with planting 2 plants in late March which do not die from freezing and if they are stunted they show it well (or not at all).

Stunted can be a lot of things. A difference in root growth or formation, leaf happiness, growth rate, fruit formation, a bunch of other things- on the hot end of things, it can hit the point where heat stunts the tomato and it shows with blossom dropping. It can be fairly temporary, or become chronic- depending on how the plant is treated.

For me, I start my seed indoors under lights. As I harden them off, they are exposed to outdoors during the day. Then they come inside at night when it's still too cool to me and they get their dark hardening at the same time as their day hardening. After a last few days to a week of out in a greenhouse cage as a final adjustment to the diurnal climate.. and in the ground they go. There have been seasons where they shuffle went off to the enclosed porch because the weather was just too ick. This year it's mild and they are hardening off as I type.

I usually transplant tomatoes outside around the 7th of may, the last frost date. It doesn't mean it won't get below 50 degrees at night and it will cause a time lag in growth but I'm not to concerned. and most people won't even notice a time lag. I just want to get them out of pots into the ground and in doing so I always get a time lag, a few that die and a few that stunt out. It could also be contributed to a combination of low night temps and low soil temperature preferring 60 degrees as a minimum. Toward the end of May I pull the stunts and dead and replace them with store bought plants and they seem to always catch up with the early plants. If I plant late I never get a stunt and seldom any that die. ( I do plant 40 to 50 plants.)

Peppers are the last thing I plant sometimes in the first week of June because they prefer 60 degree night temps and 65 degree soil temps. or may cause slow growth and stunting. All I gain when planting peppers early are more stunted plants. And if Planting with flowers or hanging fruit they're basically dead in the water until those peppers are removed. I always thought the stunts were caused by a virus until I learned better.
I would never do the light bulb in a cardboard box trick like VGKG because I would forget to turn on the bulb or turn it off, but it will give you a head start on a few plants. A 100 watt incandescent light will emit 341 Btu's and cardboard has a higher resistance to heat loss then fiberglass insulation per inch. Think about layering your boxes with more cardboard layers or a box in a box in a box and you could use a lower wattage bulb.

Zone 6a, have planted tomatoes May 1st every year with no problem. Grew like weeds. Hugely productive.

I planted out my peppers in early March when they were 5 inches tall. They've been through 40F nights several times. They are now 2 feet tall, and LOADED with peppers. No question they didn't grow much on those cold nights, but who cares? All this blather about peppers being damaged by such temperature is just that. I suspect the same is true for tomatoes.

Kevin I wouldn't use cardboard either, too weak and flimsy. These are hard wood boxes and the light is suspended near the center away from the container and the plants. A remote thermometer keeps me posted on the temp and I'll adjust the air exposure/vent to keep it in the 50's range. It just goes to prove that I have too much time on my hands in March.

It really depends on where you are located. Here in the south, our soil temperatures stay high so the tomatoes are not stressed when the air temperatures get down to the 40's. We had 4 days in a row with lows in the mid 40's the second week in April. Low soil temperatures never went below 63 degrees. If we waited until after then to plant tomatoes, we would never produce many if any tomatoes since the June heat and humidity will prevent fruit set.

I planted the first week of March, had to cover the tomatoes twice since the temperatures went down in the mid to upper 30's. Now my tomatoes are 4 feet tall loaded with tomatoes that are beginning to produce. Again, would not work the same further north or along the west coast, but works well here.

Farmers here complain about low soil temperatures stunting their crops, not a one time low unless of course they get a freak frost.

Gary's comments are right on. Our soil temperatures never get much below 60F once the danger of frost has passed. No doubt that prevents tomatoes from being stunted at what would otherwise be considered hurtful temperatures. Now, while our growing season for most summer veggies (no frost) is nine or ten months, our growing season for tomatoes is VASTLY shorter, because the tomatoes won't set fruit in our summer heat. I plant out in late February, which is slightly risky, and we're all done in June. One can try for a fall crop, but planting out tomato seedlings when the temps are over 100F is pretty iffy. Sort of a joke around here when we hear northerners proudly announcing their first tomatoes by early July.

It is about SOIL temperature. Zone 5-6 is a whole heck of a lot different than zone 9. Up here the ground is frozen for a couple months during the winter -- it takes time to warm in the spring as well as dry enough so it's not sopping-wet. Cold, wet soil is death to some plants; cool, wet soil might be tolerable but plants that need warm soil will sulk.

Yea sure you can manipulate things with all sorts of tricks. I tried the wall-o-water a couple years in a row and guess what? I got tomatoes no earlier than just waiting until the soil was thoroughly warmed before planted. Well, maybe a week or so earlier -- but getting tomatoes a week earlier wasn't worth the effort I went through setting up the contraptions. I have too many other things to do than fiddle around and coddle the tomato plants.

I grow tomatoe seedlings under lights indoors, start hardening off sometime in early May, depending on weather, and usually plant out 3rd week of May. That is typically when the SOIL has warmed enough to promote rapid root and plant growth. There have been times where I've waited until Memorial weekend because the weather and soil temps just didn't cooperate.

Melons don't go out until 1st week of June. Melons HATE cool soil, and if it's a relatively cool, wet summer fuggedaboutit = accept that it's a bad melon year and let it go.

This is true, but that's not an issue of nighttime air temperatures, as in a weather issue. Soil temp is largely a climate issue. I think the point is that warm soil can let you get away with a lot in regard to cool air. Now, soil temp is also a matter of soil content. I dig in loads of not-completely composted material, and it continues to compost in situ, and heats the soil. So my soil is slightly warmer than the mean local soil temp. No nutrient worries. I routinely add nitrogen. I plant out my melons in mid-March, with soil temps in the low 60sF and yes, they're slow until it starts warming up. They are now exploding, with my soil temp near 80F.

^^ I bet you guys in the south can grow spectacular-tasting melons! Not so much up here....some years are good, some ok, and some years like I said just forget about it and hope for the best next year.

Yeah, they're spectacular, if we get them before the possums and raccoons do. Cantaloupes SMELL ripe, and the beasts know it. Often, that's how I identify a ripe cantaloupe. When it has a big bite taken out of it. This year I have chicken-wire fencing up. Fingers crossed. I have marble-sized melons already. I also grow Armenian cukes (which are really melons) and have already harvested a few.

" Zone 5-6 is a whole heck of a lot different than zone 9. "

Only as it pertains to how cold it may get in winter. While my zone 9 climate has mild winters and rarely does the ground freeze more than an inch or so in extreme (for us) weather, it also remains cool in summer and it takes a long time for the soil to warm up sufficiently to be able to plant out tender, temp sensitive plants like tomatoes. That requires a period of time where night time temps remain above 55F and that doesn't occur before late spring - mid May to early June.

That's very true. I used to live in the PNW, and now live in Texas. Zone 8/9 in BOTH places, and while winter is similar temperature-wise, summer is HUGELY different. People often think that the USDA zone is a convenient indicator of climate. NOT SO. It's simply how cold the winter is. It has nothing to do with summer gardening.

It doesn't matter where you live, the top 4" of soil will lag air temperature by 4 to 6 hours. Folks in Zones 7 -10 will see their top soil temps fluctuate just as fast as zones 3-5. I just happened to check soil temps yesterday hoping to plant some sweet corn, and with air temp at 65 degree the soil temp 5" down was 60 degrees. I would of planted if the weather forecast looked better. Last night air temp dropped to 42 so I checked soil temp 5" deep and was only 49 degrees at 8am, a 11 degree drop!. Today's high will only be 50 with tonight's low will be35, so Sat. morning the soil temp will be around the low 40's. This is how fast soil temp move and would have killed my corn seeds.
I need 60 in the soil for at least 48 hours when planting sweet corn to avoid imbibitional chilling to the seed. Absorbing water colder than 50 degrees in the first two days will damage the seeds and won't germinate even when it warms up later.
So about tomato seedlings, soil temperature is proportionally relate to air temperature and the only way around it is insulating the ground before it follows air temperatures. soil below 60 will drastically reduce nutrient uptake and also proportional to temp until uptake stops. The result is the plant stuck in time until temps go up. I started my tomato and pepper seeds later than I ever had, chasing early planting isn't worth the work.

I'm not sure if that's right in practice. We had a cold front come through in early April, and the nighttime air temperature dropped to 40F from a daytime temp of 70F. It was 50F at 10pm. I can look all that up. The minimum soil temperature on that following morning (5 inches deep, at a local sensor station that records continuously) was 59F. I can look that up. I don't keep track of my own soil temperature anywhere near as continuously, but that sounds familiar. Now, as I said, suitably amended soil can generate it's own heat, and that might be a factor here. Now, it may also be that deeper layers were warm because of previously warm days. But this means that the soil temperature won't just depend on the current air temperature, but also the air temperature in previous weeks. So if we're talking about a sudden cold front coming through, your soil temperature won't track the air temperature very well, and may not ever drop even close to the air temperature at all.

BTW, I've posted this before, but Greencast does a nice job assessing local daily soil temperature. Don't bother trying to measure it yourself. https://www.greencastonline.com/tools/soil-temperature. Not quite sure where they get it, but it could be derived by integrating air temperature over time. USGS has many real-time monitors around. You could look for one close to you.

The average depth to reflect the 100 year average air temperature is 25 - 50 feet down. Everything above is based average air temperature for a specific time duration to the top 4-5 inches and determined by the average temperatures over hours.

I took the soil temp at 4 pm this afternoon when air temp was 49 degrees. It was 52 degrees, and I'll do it again Sat. morning when it's 35. With the 4 to 6 hour lag the soil temp should be 40 or below.

Gardengal, have you had severely stunted tomatoes and peppers that never grow again like you have warned people about for years? I have read you say that you have not worked in or dug in ground for more than 20 years, that you just use pots. Did you have this stunting issue back when you planted in ground?

We're not talking about 100 year averages. We're talking about the heat wave that preceded the cold front by a week. I agree that the temperature will stabilize 4-5 inches down after 4-6 hours, but it will likely NOT stabilize at the air temperature, if the air temperature has changed suddenly.

It didn't get down 35 as predicted. This morning at 7 am it was 43 degrees and the soil temperature was 45 degrees, another 7 degree drop.

A real time top soil site shows your top soil temp oscillates just as Mine does due to air temperature change and dives like a bird when cold fronts move in.

Top soil will track the air temperature closely. 5-6 inches down, it won't necessarily. We're talking about soil where the roots are.

I know during smowmegedon we got down to 14 and 16 degrees on back to back days, but the top of the ground did not freeze. Same for the other couple of years when lows got down to 12 to 13 degrees. Once several years ago the top of the ground did freeze, but only for the morning and only for part of one day. Soil temperatures here stays in the 40's and 50's, so when a cold snap hits we still have a lot of heat and moisture. That heat radiates up and keeps the crust of the soil warmer than it would in colder zones. Our cold snaps where I am at only last for 3 or 4 days before things warm back up with highs in the 60's.

My strategy up here in z4 is to plant some of the hardened off tomatoes in early May (this week) and some peppers mid-May (next week); the remaining plants stay indoors/haul them all out in morning, planted out in a couple weeks. If there's going to be air temps below 45 I put one of those large 3-layer paper leaf bags over the plant. I also have about 6-8 inches of straw mulch at base of each planting bed. There was one year where tomato plants leaves got damaged, but they re-grew from the roots. We have such a short season up here, I figure I gotta gamble a little bit.