Soil temperature

So here's a newbie question... Is there a way a person can determine soil temperature? I understand the obvious "get a thermometer" response, but at the moment am reserving the meat thermometer for kitchen/culinary use (and I actually don't think it is capable of a reading down in the range of our current chilly reality in the PNW).

I guess my question would better be posed as... is there any correlation between air temperature (what we see in the weather forecasts) and soil temperature?

My question comes from looking at the back of my seed packets, and even some of Mel's comments in ANSFG that read: plant when soil temperature reaches 50 F (or whatever temp is appropriate).

I can absolutely go out and acquire a thermometer, but was just curious if others' prior experience could be helpful.

I also suppose that, not being in the ground, SFG beds might have higher temps earlier in the year, just like containers. And of course location and what the bed is made of contribute to soil temps as well.

Many thanks!

I push the limits when it comes to getting stuff in the ground in winter. (cool crops) I'm super conservative when it comes to getting warm crops in the ground in spring.

My favorite crop is corn. It's optimum germination temp is 60* plus. I'm afraid that if I stuck a thermometer in the ground, I would never see that temp. Ignorance is bliss. When I feel that summer is here, it's time to plant. Sometimes I win; sometimes I lose.

One thing is guaranteed: I'll know when the optimum planting time is, about 30 days after it has come and gone!

Boffer and I have similar gardening styles. Optimum planting time for me is usually a month or so earlier than when I do. Ah well...what can you say.

It is true that germination results are better when the soil is warmer for some crops. If it is too cold, some seeds just rot. If at all possible, follow the charts. My husband has a thermometer from the days when he had a darkroom for developing his own photos. It is very accurate and quite long (11 inches) so it is easy to use. He uses it to take Gomer's temperature (the compost pile) but it also works for the soil. However, I usually forget to use it. You are probably right about the meat thermometer.

Naturally as the air temps come up in spring, the ground warms up too. But we can sort of push it a bit by doing things to help warm the soil faster. Raised beds warm up faster than those that are not raised. Another great trick is to put clear plastic down on top of the soil. The dark soil attracts the heat of the sun and the plastic helps hold it there rather than just dissipating. It is amazing how much warmer the soil feels to the touch doing that. I have had fairly good results just cutting a hole in the plastic and planting through that. I have left it on for a couple of weeks to help retain heat and remove it later. It has the added benefit of keeping cats away.

Gwynn

It's a good question but one to which there's no easy answer becuase each garden has it's own microclimate and it depends if and how a gardener manipulates their conditions. Soil temp is cooler than air temp so air temp has to reach a given point and remain there before the soil warms up.

The thing that raised beds, containers and borders tended from a path have in common is that they drain better and are darker in colour due to their compost and manure content and as a result retain heat better and have the friable, open soil structure that promotes them warming up earlier.

You can sense when things have warmed up and conditions are right by what you see and feel but it's less obvious when that point has been reached unless you stick a thermometer in. The alternative to waiting for nature to provide is to help her along.

Yes, there IS a correlation. However, it is complex and not likely to be expressed in a simple formula.

Both soil and water temps have a lot to do with your sun angle as well as the ambient air temps. The more intense the sun angle, the better both warm up. And, as we know that angle is constantly changing. When factored in with cloudy days, partly cloudy days, diurnal temperature changes, it just becomes too complex to figure with scratch paper and a pencil.

I learned this when I jumped in a lake as a teen one 82* day in October. I thought it would be a little cold, but had no idea how freezing the water would be. My father had to explain the relationship between water absorbing heat, the longer nights, and the correlation with the sun's angle to me while I was recovering from my hypothermia....lol. I never forgot it. Bottom line: The long nights never gave the sun's weak angle enough time to put significant heat into the water.

You are right. The easiest way to monitor soil temps is with a meat thermometer. There are pretty inexpensive varieties that go below 32*F. I have one, and when I want to use it for purposes non-food related, I make sure I wash it well before using it on food again.

Hmmm. Forgive me for jumping in with more questions. I just planted a bunch of corn over the weekend, and am thinking now that it may not be warm enough yet. Ah, so much to learn still... so it's been in possibly too-cold soil for 4 days now. Would covering those squares at this point with plastic save them? Would any kind of plastic work, or do I need to make a special trip out to Lowes (my second home these days)? I'm thinking grocery bags or milk cartons.

I'm not familiar with your climate to be able to say when is the best time for you. But, for me, corn is one of the last warm crops that I plant.

I use black plastic on my corn patch to help warm the soil and keep down weeds. They say that clear plastic does a better job of warming the soil. Any type of plastic will work, bags from the dry cleaners, painter's plastic, grocery store bags, even saran wrap for just a couple squares.

I've had corn sprout much faster than I expected under black plastic. They got to eight inches tall before I peeked...the stalks were white! Pretty strange looking, but they greened up in a week in the sunshine.

Thanks to all those who responded -- and so quickly! I'm grateful for the information and personal experiences, but especially for the humor. It's relatively early in the day, and I'm tending to my first cuppa joe, and absolutely laughed out loud at a few of the responses. A wonderful way to start my day. I think we could bend a phrase to read: "the worst day in the garden beats the best day in the office".

I think I'll sink my cold weather seeds now (just built my beds a week ago and filled them with gorgeous MM this last weekend), but hold off a while before the warmer weather crops. And I'll contemplate the idea of plastic, too. I read a couple of comments in the book about putting plastic tunnels over certain seeds (peas were one example), but wasn't entirely sure about how to do that. Plastic over the whole bed would sure accomplish that!

THANK YOU ALL!!

jazzymaddy wrote:Hmmm. Forgive me for jumping in with more questions. I just planted a bunch of corn over the weekend, and am thinking now that it may not be warm enough yet. Ah, so much to learn still... so it's been in possibly too-cold soil for 4 days now. Would covering those squares at this point with plastic save them? Would any kind of plastic work, or do I need to make a special trip out to Lowes (my second home these days)? I'm thinking grocery bags or milk cartons.

Jazzy,
I received this information from the Dept. of Horticultural Science @ NCSU. I thought it might help you out a bit with future projections. I would also encourage you to check with your local agricultural extension office. They are a great resource when trying to determine what and when to plant.

http://www.ces.ncsu.edu/depts/hort/hil/pdf/hil-8103.pdf

The second page suggests varieties of vegetables and the third page suggests planting dates. I am almost positive you can get something like this for your state. I hope this helps.

Jazzy,

You should be fine with Corn here and planting right now. A local corn farmer here plants about 15 acres of it and its on my drive to work each day. His crop is already a few inches right now. I actually use him as a reference guide. When he tills over the soil usually sometime in late Feb, that is my cue to get busy with my spring transplants. When I see corn poking out of the soil, its time for summer plantings.

Oh, that's awesome. I actually went out and checked on my corn today (I went ahead and covered those squares a few days ago), and I HAVE THREE BABIES!!! Well, baby corns that is. I already knew about my three human babies, and I didn't cover them in plastic, unless you consider some of the cheapy diapers I used once in a while...

So I guess I should go ahead and take off the plastic now. What could I do to cover my broccoli toddlers so they will bear before it gets too hot? Anything?

Thanks again staf.

Oh, and thanks to you too, buttaflie. I didn't see your response. I'll definitely look into that. I need all the sage advise I can get! And rosemary advise if they've got it...

Don't forget the thyme

jazzymaddy wrote:Oh, and thanks to you too, buttaflie. I didn't see your response. I'll definitely look into that. I need all the sage advise I can get! And rosemary advise if they've got it...

You're !!!!!

Furbalsmom wrote:Don't forget the thyme

The thyme, the thyme, who's got the thme?