Hardening Off......Temperature Guide ?

[Noreaster]

Could use a little advice here.....once my need/temptation to move seedlings outdoors for hardening sets in:

Is there a guideline for what's best in terms of daily outdoor high/low temps to allow for this ?

Like 60/45 ? 65/50 ? 70/55 ? 75/60 ?

Thanks !

Noreaster (experienced, but forever learning)

[carolyn137]

I can't give you any advice re the temp highs and lows that you've posted.

All I can say is that I harden off my plants about the week before they're to be planted outside for good, and so what
's good for planting out is also good for hardening off.

Sure, sometimes it turns nasty with heavy rains or even sometimes with late frosts, but I keep the plants where I can protect them from adverse conditions.

I'd rather have the bad weather come when they are all together as seedling being hardened off rather than trying to deal with that when they're already planted out, which I never could do considering the number of plants I used to put out.

You say Noreaster but no growing zone is given.

I'm in a generally zone 5 for 19/20 years and will NOT plant out until the first week in June if the weather looks OK.

If you put out plants too soon they're just going to sulk in too cool soil.

[Noreaster]

OK, thanks Carolyn. Here in Zone 7, planting out about May 10 is safe. So with hardening a week before, I'll do it May 3 if need be.

Lets see, they'll only be 4 1/2 weeks old by then...should be OK if they look strong enough, if not will keep inside one more week, and plant about May 17th.

Noreaster

[where_with_all]

not to steal the thread, but i was wondering what is the right soil temp for tomato transplants? Carolyn, you said that the plants sulk in too cool soil. What is too cool?

[carolyn137]

Originally Posted by where_with_all

not to steal the thread, but i was wondering what is the right soil temp for tomato transplants? Carolyn, you said that the plants sulk in too cool soil. What is too cool?

I have no idea what the temp of the soil might be when I plant out. I am not a person who takes temps, counts fruits, weighs fruits, or gets into the pseudo-scientific way of growing tomatoes.

I just know when the soil is OK to plant b'c I don't fool around planting out early with WOW's and all that. Been there, done that. I'd rather not have early tomatoes at the expense of waiting a bit longer for great tasting ones since most, but not all, earlies are not known for taste. At least in my growing experience.

The soil temp is a reflection of ambient temps so that's the way I know when it's OK to put them out.

Non-scientific? For sure, but I'll be 68 in June, was raised on a farm where we grew lots of veggies and fruits and I guess when to do this or that is just part of my past experiences.

Sorry I can't be more specific as regards actual soil temps.

[where_with_all]

pseudo-scientific??

what is pseudo about taking soil temperature? Not sure I understand that comment

Carolyn- maybe you don't prefer to garden scientifically . Thats ok. I can respect that. Your experiances in life guide your actions. My experiances are different. I need to have some science around it. Can anyone else chime in if they have any experiance here.

I agree that early season tomatoes lack taste. The purpose of the question is so that I get my LATE season tomatoes in time before the weather cools in September. I would bet, that being from upstate NY, your growing season is about the same or shorter than mine. I have to believe you have run into this problem with some of your late tomatoes being harvested at the end of september and suffering from overnight cold spells. Especially if you transplanted in June.

God bless, 68 and still gardening. Wonderful.

[dcarch]

Originally Posted by where_with_all

pseudo-scientific??
what is pseudo about taking soil temperature? Not sure I understand that comment------.

In the context of Carolyn's post, I do not think that she meant taking soil temperature is pseudo-scientific at all.

In any case, soil temperature is somewhat complicated:
1. Ambient temperature changes soil temp.
2. Porosity of soil.
3. Solar exposure.
4. color of soil.
5. Recent rain fall.
6. wind speed.
7. Recent snow fall.
8. Ground water activity.
9. Air humidity (laten heat lost from evaporation).
10. May be more other factors.

dcarch

[carolyn137]

what is pseudo about taking soil temperature? Not sure I understand that comment

*****

I think dcach has nicely outlined some of the factors and variables that are related to soil temp for it isn't just sticking a thermometer in the soil and reading it.

Each season is different. In my zone 5 when I plant out at the begining of June in a good year I can mature any variety I want to, but there are those years when frost comes earlier than normal.

Most of my harvest would be from late August into mid-September.

As for being 68 and still growing tomatoes, well, I was until I fell in Dec 2004 and severed all four quad muscles in my right leg. New left hip last June and new right one going in in a few weeks. The details are in the thread on my health near the top of this General Discussion Forum. And I've been using a walker since Dec 12th, 2004.

So instead of growing my normal 500-maybe 1000 plants/season, Martha in VA is raising my 12 plants for me and someone else plants them, cares for them and harvests for me.

bcday in WNYS has been doing seed production for me for the new ones so I can list them in the SSE Yearbook, and Shoe in NC has also helped in that regard. And as I said Martha ( gardenmama) has been so helpful in custon growing plants for me with my sending her seed for those, although she has a very large seed inventory herself and does sell plants.

it's been a huge change in my life to not be able to garden, that's for sure.

And being a scientist myself, now retired, I meant it very honestly when I said I don't grow tomatoes scientifically. I feel very strongly that experience is the best teacher and not growing anything according to set principles.

[Suze]

General soil temp guidelines:

http://aggie-horticulture.tamu.edu/c.../soiltemp.html

[Suze]

Originally Posted by Noreaster

Could use a little advice here.....once my need/temptation to move seedlings outdoors for hardening sets in:

Is there a guideline for what's best in terms of daily outdoor high/low temps to allow for this ?

Like 60/45 ? 65/50 ? 70/55 ? 75/60 ?

Thanks !

Noreaster (experienced, but forever learning)

Well, I can't give you exact guidelines, but here are a few tips. Remember you are not only acclimating the plants to sun and outside temps, but also to winds.

I use a fan on my plants while they are growing inside. The fan is on the entire time the lights are on (it's all on a timer). I've found this makes quite a difference in producing tough, stocky seedlings that will stand up to the hardening off process better in general.

Gradual is best not only with sun, but also with temps. For example, if you've been growing under lights in a 72F room, don't shove the plants right out into a 50F day. Pick a warmish day to put seedlings out.

I don't like to have the seedlings in temps below 45F or so and will protect/put in garage at night so they don't get slowed down.

Of course, odds are high that they will have to eventually have to take one or more nights at lower temps than 45F after planted, so don't pamper them temp wise too much. Towards the end of the hardening off process, make sure they are able to take some coolish night temps.

Hope this gives you more of a feel for hardening off your seedlings.

[where_with_all]

Originally Posted by dcarch

In the context of Carolyn's post, I do not think that she meant taking soil temperature is pseudo-scientific at all.

In any case, soil temperature is somewhat complicated:
1. Ambient temperature changes soil temp.
2. Porosity of soil.
3. Solar exposure.
4. color of soil.
5. Recent rain fall.
6. wind speed.
7. Recent snow fall.
8. Ground water activity.
9. Air humidity (laten heat lost from evaporation).
10. May be more other factors.

dcarch

darch,
Thanks for the note-- but to be accurate, taking soil temperature is a scientific and accurate processs. There is nothing complicated about it. Stick thermometer in, wait, and read temperature. The process has little variability.

All the things you mention have to do with effects (or affects?) on soil temperature. These variables would be a problem if you were trying to predict soil temperature.

I would also suggest that the variables you identify are not that big a deal. Soil tend to have a high thermal mass so there are usually limited transients in temperature.

Just from my own limited experiance this year, I have noticed that soil temperture is gradually increasing everyday with less than 5% variation in time of day, rainfall, etc.

To account for all these factors- transplant when the soil reaches 63 rather than the 60 that is in Suze's link (thanks Suze)

Or you could do what maybe carolyn does- and wait for the forsynthia blloms to drop to tell you it is time to transplant.
Either way works

But if your are trying to get a jumpstart by heating the soil with plastic wrap then you need to take the temperature.

Carolyn- I am jealous- All my tomatoes taste bland if they are allowed to ripen after labor day. The cooler temps seem to ruin them. How do you do it?

[carolyn137]

Carolyn- I am jealous- All my tomatoes taste bland if they are allowed to ripen after labor day. The cooler temps seem to ruin them. How do you do it?

****

I see Labor Day as being an arbitrary date.

As long as the night temps don't go too low the fruits are fine, but once the temps get down to the 40's and low 50's at night then I have problems with anthracnose and in addition the fruits start to become watery and shall we say "icky" tasting.

When most of the fruits get so watery I don't want to eat them, not that I would anyway, and they were used for seed saving for my SSE listings and online seed offers.

Was it last Fall we didn't have cool temps enough to make them watery and icky until almost the middle of October? I think so.

[moulman]

Wow, Carolyn!

In my area we rarely get night time low temps above 55F- 58F , even through the hottest Aug. !

And I have not had problems with fruit set or flavors.

[montanamato]

I am often surprised when people start to panic at temps in the 40's too...There is usually only a few weeks each summer when the night time lows are above 50 here...Then daytime highs are often in the low 90's for weeks...Fruit set and flavor for most is good for me too...Practically no humidity may help, but I have had a ton of great tomatoes into early October many years...
The tomato plants do much better with cold nights at the end of the season , than they do with cool temps when just getting established...
I have tried the wall o waters ages ago, with poor results too...I agree with Caroline, there is nothing to gain by plunking seedlings in cold ground...Now, I do try and beat the season some, by using a lot of containers and a cold frame for some smaller determinate or dwarf types...The only time I am tempted to plant into the main garden before June 1 is if I have several spare trays of backups...and that is getting too labor intensive also...Those plants put out in warmth quickly catch the pale, cold seedlings that have been doing nothing...

Jeanne

[dcarch]

Where With All,

One thing about science, as long as you identify the variables and all factors, we will be on the same page.

I don't think fundamentally we have disagreements.
Let me clarify why I think soil temp. issue can be as simple as you describe and at the same time as complicated as I feel it can be.

You are correct that soil is “massive” to stabilize thermal swing. I think you will agree that this “massive-ness” range is rather wide, depending on the composition of the soil.

All the factors I named will influence the temperature significantly and interactively depending how deep you measure into the soil. Do you measure 1”? 10”? 18” deep?

Then when you factor in the time scale relative to all the components, mathematically it becomes unmanageable.

Scientifically, as long as you are aware of all the variables not accounted for, then the information is useful within that limitation.

Practically I go with Dr. Carolyn’s methods of growing tomatoes.

Personally I feel offended by her comment that my singing to my tomato plants is “pseudo-scientific”. I am sure that my lullabies have improved production of fruits measurably.

dcarch