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Effects of soil and air temperature on vegetables

Posted by AlyoshaK 7 (My Page) on
Tue, Jun 19, 12 at 16:54

I've just recently joined and recently started gardening so this is a rookie question. In an earlier post about gardening books I came across the following response by "okiedawn":

"It was this book that taught me about the effect of soil temps and air temps on plants, which may seem elementary, but most of us don't know those things when we're just starting out. Once you understand the effect of air and soil temps on your plants and their productivity, everything else just falls into place."

The book referenced was "The Vegetable Book" by Sam Cotner. I had no idea this was so important. Worse, that book is hard to find and expensive. Cheapest used one I've seen is $94.00. Can anyone recommend some resources that will enlighten me about this part of gardening, and how everything falls in place after it?

AlyoshaK


Follow-Up Postings:

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RE: Effects of soil and air temperature on vegetables

AlyoshaK,

Uh oh. I bet the book is out of print. It went out of print once before and at that time Dr. Cotner said he did not think the publisher ever would print it again because it is a very, very costly book to produce because of all the photographs. (The book itself is 421 pages, and every chapter has several photos.) Later on, though, the publisher did another printing of the book and that's when I got my second copy (a hardback version) for less than $30.00 because my first copy (a paperback version) was falling apart after many years of use.

Your best bet will be to catch it on a used book website or in a used book store in the winter time when no one is gardening and no one is looking for this book. When I still lived in the Dallas-Fort Worth area, I often would see used copies of this book in the Half-Price Books stores in the area. I don't know if the Half-Price Book store in OKC would have it, but if you're ever in there, it is worth watching for.

I suspect the publisher decided not to do another print run of this book, which originally was published in 1985, because a current author of theirs who also writes for their Texas Gardener magazine has a new fruit and vegetable book that was just published. It may be that he wrote the book as a newer replacement for Dr. Cotner's book because they knew they weren't going to print any more copies of it. I haven't seen his book, so cannot tell you what it is like, but Greg Grant is one of my favorite regional garden writers.

The publisher for Dr. Cotner's book, when it still was in print, was Texas Gardener Press, which I'll link below. I did a search for his book on their website and they told me it no longer exists. I'll link the website, though, in case you want to see the other regional books they offer.

With regards to the effects of soil and air temps on various veggies, is there a specific vegetable you're interested in right now, or just all of them? If there's a specific one, let me know what it is, and I'll explain how temperatures affect it.

Dawn

Here is a link that might be useful: Texas Gardener Press


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RE: Effects of soil and air temperature on vegetables

No, no specific vegetables in mind because I'd like to grow quite a variety, mostly the usual stuff. I used the BookFinder site which searches far and wide, and was surprised at the expense of all the results. I can visit a Half-Price store in FW and look for it.

I would like an extensive, comprehensive understanding of this since you seem to think it's so important. So, without a book, I'll have to start scouring the web. Perhaps you can give me some key concepts or terms that'll help my search. Surely on the entire world wide web there has to be some good information.

Is it just a few pages of info in the book? If you're able and willing to photocopy the pages I'll gladly pay you for the image files. Just a thought.
AlyoshaK


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RE: Effects of soil and air temperature on vegetables

I found this chart! It lists, among other things, minimum soil temps and preferred air temperature range for germination, for various vegetables. Is this perhaps what you found so valuable in Dr. Cotner's book?

http://www.gardeningbythemoon.com/chart.html

AlyoshaK


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RE: Effects of soil and air temperature on vegetables

AlyoshaK,

Minimum soil temps and preferred air and soil temperature range for germination are important, and Dr. Cotner's book includes some of that data but also includes data on what temperatures are best for fruit set, etc. Each of the 31 main chapters in his book focuses on a specific vegetable, and throughout the chapter, he'll discuss the different affects both air and soil temps have on vegetable plants, and he does mention minimum germination temperatures but not in exacting detail. Most of us use Tom Clothier's seed germination database for the really detailed soil temp/seed germination info. I'll link it below.

I like Dr. Cotner's book a lot and have considered it a valuable tool for many years, but I wouldn't spend $84 to buy it. There's lots of great vegetable gardening books out there for a reasonable price, and I do not consider that a reasonable price.

If you just follow along with current threads on this forum, especially in late winter and early spring, you'll see all of us talk about if the air is warm enough, if the soil is warm, etc. in terms of planting the various vegetables. Then, throughout the the year, we talk about the heat's effect or the cold's effect on whatever we're doing or whatever is going on in the garden. You can learn the temperature stuff that way.

I grew up in a gardening family so I knew, for example, that we always planted potatoes on or near Washington's Birthday. No one ever explained why, and as a kid, I didn't ask. I just knew that you planted them at that time. When I read Dr. Cotner's book, he discussed how potatoes make their best growth with daytime temperatures are between 60-75 degrees during the day and 45-55 degrees at night. He also said that in order for potatoes to make a good crop, they need to set and size their tubers before soil temperatures begin exceeding 85 degrees. So, you see, based on what he said about the air temps and soil temps, I understood that my dad planted potatoes on Washington's Birthday because that was the time you needed to plant your seed potatoes so your plants would be making good growth when the air temps were in the right range and so that they would have time to make a good crop before the soil got too hot. It was the same in every chapter---Dr. Cotner's scientific explanation helped me understand why my Dad planted onions when he did or peppers or corn or tomatoes when he did. I grew up knowing the old folk explanations--like you plant your corn when the oak leaves are the size of a squirrel's ear, but realistically speaking, Dr. Cotner's temperature explanations are a lot more useful, especially since I'm gardening in an area further north than the city where I grew up and learned to garden.

A lot of the temperature-related information, you sort of discover as you go along. Finding it in his book just moved me along the learning curve a little more quickly. For example, once it gets really hot, you might notice that tomatoes are slower to color up in the heat. OSU did research that showed once the air temps are staying at 86 degrees and above, the heat has a negative impact on the way tomatoes color up. It can slow them down and it can cause a sort of patchy color on the fruit (as can some pests and some diseases/genetic issues like 'gold fleck'). After I read that, I understood why my dad would pick tomatoes after they'd broken color and he'd bring them inside and set them on a counter to ripen. It was because they'd color up faster inside, and clearly he knew they ripened better inside and he was doing it long before OSU did their research. After I read about the OSU research, I understood exactly the temperature that can begin to slow down the coloring up of the fruit. It didn't change anything I was doing because I've always liked to pick at breaker stage, but it helped me explain it better when someone else asked why. So, I think there's a lot you learn by observing and doing but it is nice to read the books and understand why you're observing whatever it is you see.

I'm going to link Tom Clothier's database on vegetable germination.

Dawn

Here is a link that might be useful: Tom Clothier's Seed Germination Database


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RE: Effects of soil and air temperature on vegetables

I'm so far north that I drool for a month while everyone talks about BLTs. I have had cherry tomatoes and small salad size for awhile now, but only today do I finally see color on some of the big slicers. It sure takes a long time from seed to sandwich for those big ones.


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RE: Effects of soil and air temperature on vegetables

I'm glad you're seeing the color change. The first real BLT featuring a huge slice of tomato is merely days away now. I'm happy for you. I hope you and Al enjoy and savor every single delicious bite.

The big ones do take a awfully long time some years and in a year I expect severe drought, I'll skip planting the really big ones....the ones where only a single tomato slice covers a whole piece of bread. This year, with all that rain falling in Jan-Mar, I planted oodles of big ones and I am glad I did. It is a good year here for big tomatoes. I don't know if that is a true in the parts of the state with below-average rainfall.

I don't care how many big tomatoes you get later, or how many BLT sandwiches you enjoy over the course of the growing season, the first one is always the best--if only because you waited so long for it!

The bite-sized tomatoes started splitting after the last big rainfall, but the big ones only showed some mild concentric cracking beginning this week and it was not bad enough to ruin the fruit...it was almost like the heat checking you see where the skin doesn't actually tear, but comes very close to it. I don't think I'll have to worry about any more tomatoes cracking from rainfall, because it is drying up and heating up and I'm afraid the garden will begin to suffer accordingly. It's all good, though, as long as we're getting tomatoes of any kind.


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RE: Effects of soil and air temperature on vegetables

It looks like I am going to get a nice harvest of tomatoes that set early and are just now starting to change color, but a lot of my vines look very unhealthy. That little bug infestation probably did some harm and I haven't had rain for a long time. I am trying to keep them watered, but the ground is so dry, it soaks it up fast. I'll just enjoy what I get and not worry about it.


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RE: Effects of soil and air temperature on vegetables

Dawn,

Thanks so much for your post, particularly what you said about potatoes and the seed germination database. I did check out Greg Grant's book on the previous link, but even after going to Amazon where I could examine it more closely it didn't seem say much specifically about what I'm interested in. It said a little, but not much. Since your such a tomato specialist do you have any particular observations with regard to tomatoes and temperature?

AlyoshaK


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RE: Effects of soil and air temperature on vegetables

Dawn,

Thanks so much for your post, particularly what you said about potatoes and the seed germination database. I did check out Greg Grant's book on the previous link, but even after going to Amazon where I could examine it more closely it didn't seem say much specifically about what I'm interested in. It said a little, but not much. Since your such a tomato specialist do you have any particular observations with regard to tomatoes and temperature?

AlyoshaK


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RE: Effects of soil and air temperature on vegetables

Temperatures affect tomatoes in many ways.

SEED GERMINATION: Tomato seeds need soil temps of 70-75 for best germination.

FREEZES/FROSTS: Tomato plants cannot tolerate freezing temperatures and will freeze at 32 degrees. Tomato plants can be damaged by prolonged frost exposure, although they'll often survive a small amount of light frost for a short period of time. Because of our erratic spring weather, it is recommended that you wait 10-14 days past your average last freeze date to transplant tomato plants into the ground. However, a lot of us plant on or even before our last frost date or last freeze date because we're trying to beat the heat for pollination/fertilization purposes. I'd only do this if I felt like I could cover up the plants well enough to protect them from an unexpected freeze or frost. I watch my weather very carefully after my tomato plants have been transplanted out because, under certain conditions, you can get frost and frost damage on tomato plants at 37 or 38 degrees, even though the temperatures are above freezing. I use Agribon floating row cover that gives 4-8 degrees of freeze/frost protection if a freeze or frost threatens after my tomato plants are in the ground or in large, unmovable containers.

SOIL TEMPERATURES: Soil temperatures should be staying consistently at or above 55 degrees before you put your tomato transplants into the ground. In soil that is colder than that, the plants will stall and sit there and be miserable. Sometimes it stunts them and they grow poorly for the rest of the year.

POLLINATION/FERTILIZATION: Tomato flowers are pefect flowers, meaning they fertilize themselves from pollen formed within one part of the flower. High temperatures can bring pollination and fertilization to a halt. How high? It varies. For some tomato varieties, the threshold might be 92 degrees, but for others it is about 95 degrees. At the same time, nighttime low temperatures above 72-75 degrees can prevent pollination and fertilization. Generally, the larger the fruit that the plant produces, the less likely it is to set fruit well at higher temperatures. Generally, the smallest tomatoes, generally referred to as cherry tomatoes but also in shapes/sizes called currant, grape, and pear, will product fruit in hotter temperatures than the plants that produce full-size fruit.

In much of Oklahoma, we reach those temperatures in June of most years. In some years when it gets too hot too early, like it did last year, those hot temps can arrive in April or May. That's why we push hard to get the plants into the ground as early as we reasonably can without losing them to a freeze, frost or late snowfall.

If you can keep your plants alive throughout the summer's extreme heat, drought and onslaught of pests, the plants will flower, pollinate and fertilize in late summer or autumn after temperatures drop back into the preferred range.

HUMIDITY TOO: It isn't just the heat, but also the humidity, and especially the two of them together. High humidity can make the pollen 'sticky' so it clumps together and refuses to move around inside the flower and do its job. The worst combination is high heat/high humidity. In some years when my county has been in Exceptional Drought, even when daytime highs were above 110 and nighttime lows were in the 80-85 degree range, I have had tremendous amounts of polliantion and fertilization on tomato plants, usually in August. Why? Because we were so dry that our humidity was in the single digits in the afternoons and fairly low the rest of the day. So, high heat/very low humidity is not nearly as bad, in terms of fruitset, as high heat/high humidity.

When it gets hot, sometimes you can help your plants achieve pollination and fertilization by thumping the flower blossoms to shake up the pollen inside the flower. If you have a lot of plants and it would be ridiculous to try to thump every flower, you can just gently shake the plant to get the same effect. If your garden is getting wind, the wind likely is doing this tast for you. Texas horticulturalist Neil Sperry used to recommend that people with rows of caged tomato plants walk along the path beside each row and whack each cage with a tennis racket as they walked by to shake up the pollen.

TEMPERATURE'S EFFECT ON TOMATO FLAVOR/TEXTURE: Nothing will ruin the flavor or texture of a fresh home-grown tomato (or, for that matter, any tomato) more than refrigeration will. I never, ever under any condition put my home-grown tomatoes in the refrigerator because it turns them into mushy, poorly -flavored grocery store tomatoes. Why go to all the trouble to raise tomatoes if you're going to put them into a refrigerator? Dr. Adams says in his book "The Texas Tomato Lovers Handbook" that if you simply must refrigerate tomatoes, just remove them from the fridge 2 hours before you eat them and it will improve their refrigerated flavor somewhat. I've never tried this since I refuse to refrigerate my tomatoes.

INSECT PEST BEHAVIOR: To a certain extent, the tomato pests you see on your tomato plants are linked with temperatures because some pests are more common in cooler temps and others are more common in warmer temperatures. Early in the season, the tomato pests you're more likely to see are flea beetles, cutworms, aphids and often leaf miners. As the warmer weather arrives, you start seeing other tomato pests that are heat lovers like spider mites, grasshoppers, stink bugs, blister beetles, leaf-footed bugs and tomato fruitworms, pinworms and hornworms.

BLOSSOM DROP: Most tomato plants will drop their flowers without the flowers forming fruit if air temperatures are staying at or below 55 degrees. So, even if the soil temps are good and the plant is growing, you may not get fruitset until the temps are consistently staying above 55 degrees.

CATFACED FRUIT: Rough, misshapen fruit is called catfaced fruit and it is common when tomato plants manage to bloom and set fruits at temperatures below 55 degrees. There's nothing inherently wrong with the tomato fruit, but sometimes there is so much tissue scarring in the catfaced areas that a portion of the fruit is not edible and must be discarded.

DISEASES: Many tomato diseases can develop only in specific temperature ranges, so there's some diseases we are more likely to see in cool, wet spring weather but other ones that are more common in warmer weather. Knowing the temperatures at the time a disease develops can help us diagnose a disease. One reason we tend to escape tomato late blight here is that we're usually too hot for it to develop.

HEAT IMPEDES GOOD FRUIT COLOR: Any time the air temperatures are 86 degrees or higher, the coloring up of tomato fruits tend to slow down. You also can get uneven ripening where some parts of the fruit look fine and others just won't get their fully ripe color. Generally the hotter it gets, the more this is a problem.

COOL TEMPERATURES IN FALL: While we often get a second chance for a tomato crop with fall tomatoes, fall's shorter day length and cooler temperatures can have an adverse effect on flavor. The fruit that ripens in October, for example, usually is not as tasty as fruit that ripened in June or July, unless the October weather is unnaturally hot.

Hope this is the kind of info you were looking for,

Dawn


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RE: Effects of soil and air temperature on vegetables

Dawn,

That is exactly the kind of information I was hoping for. My sincere thanks. Now, to find a copy of that book so I'll have more guidance on the other vegetables too.

AlyoshaK


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RE: Effects of soil and air temperature on vegetables

Well, well, I found a copy of Cotner's book! And for only $13. Had to dig around some though. If I don't get to garden in OK this fall, I should be up there in the spring (near Durant). We'll see how things go. I really like the camaraderie between the gardeners on this forum. Perhaps one day I can join the club so to speak and contribute something myself. Right now I make my living at a computer and I live north of Dallas.

AlyoshaK


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