Vegetable Planting Guide

Soil temperatures are important for indoor germination, where the Table is useful, but also for outdoor germination, which is what they are supposedly talking about.

If I thought the minimum temperatures were going to produce a sprout, I better not stand there waiting for it - I'd turn into a statue. And, if I had to wait for my soil to reach optimum temperature at "at 8 a.m., 4 inches deep" -- I'd be waiting right thru the growing season and still trying to raise hell!

50°F soil will get you anywhere you want to go with cool-season crops in 1 to 3 weeks.

60° soil will do it for you with warm-season crops.

And, in my own optimistic fashion, I'm going to anticipate those temperatures by, at least, a week by sowing earlier. Soil temperature can catch up with the seeds and me if I think Happy ♪☺♫ Thoughts thru that time period!

Steve

Try as we might to convince ourselves, outdoor gardening is far from a purely scientific process. There are just way too many variables...

Throughout the Northwest, AgriMet (Bureau of Reclamation) keeps track of soil temperatures. Morning to Afternoon: at 8" into the soil on the 1st day of summer last year, AgriMet tells us that temperature varies just over 2°F in Aberdeen, ID. At a 4" depth, it varied nearly 5°. At a 2" depth, it varied over 6°.

The bureau is setting up one of these stations just a few miles from my garden. I assume that other agencies are doing this kind of thing in other farming regions. In Canada, it is the job of the Ministry of Agriculture in the various provinces, as I understand it.

Season of the year makes a difference with the greater intensity of sunlight. But, we are usually just talking about springtime temperatures for germinating seed.

Linked below, you can see the difference between average soil temperatures (morning and afternoon) during the months of April and May. It is quite a difference as they move into May but very little difference during April.

Soil moisture also changes things. Morning to Afternoon: In April, the average change is less than 8° in Lethbridge, and that is at a 2" depth.

All in the interest of providing some guidance for growing . . .

Steve

Like: the lilac leaf when the soil is 45°, my lilac bloom at 50° soil and the grape leaves are when the soil reaches 60°. Weeds are also good indicators of when safe to plant. When the goat heads sprout the soil is 70°.

If I take the temp at 8am in the same central place in the garden, then I don't confuse myself with data overload because it is just an indicator, not a cast in stone rule.

Thanks Steve for the CSU link. It is useful information, especially for people like me that did not grow up gardening, have never been farmers and don't have mentors (other then our internet friends).

They are out there everyday, all year and reacting to the totality of the environment.

We can really get crowded down into single variables and . . . I realize that this sounds like a contradiction to what I've said above but it is just part of my efforts to understand what is going on "out there."

Steve
The human understanding is like a false mirror, which, receiving rays irregularly, distorts and discolors the nature of things. ~ Francis Bacon

Are you holding your breath???

I do it whenever I have enough time!

Problem solved! Now everybody knows "when" to plant their veggies! Heh heh heh!

There is, of course, one caveat to that! There’s the cold season ones, and the warm season ones. But then, I haven’t even gotten the "warm season" side of my garden turned over yet, so the chance of putting them in "too soon" is unlikely! The problem there, however, is that the root crops go in the warm season "side," so they’re not in yet—and need to be gettin’ in soon! Altho if I HAD gotten them in with the REALLY cool season stuff, they’d probably just be sittin’ there with all the cold weather we’ve been having anyway, so maybe it’s a good thing I "didn’t have time!" At least, that’s how I’ll rationalize it to myself! And the other rationalization is: the root crops have ALL summer, and even into fall, to grow anyway, so they have LOTS of time!

What has REALLY amazed me this year is that I got my lettuce and spinach and peas in on the 18th, we’ve had mostly COLD weather since then—with lots of wind, except for a few warm days, and on the 27th I discovered that the first lettuce (Winter Density Romaine) had ALREADY come up! I almost fell over—or would that be, got blown over! Of course I had been going out there EVERY day to look—in the rain, in the snow—but I never REALLY expected to see anything up yet! The next day, on the 28th, three more lettuces and one spinach were up, and on the 29th, the first pea was up! I really was shocked! When the cold weather came in—and stayed—after I planted them, I had started worrying that they were all unhappily ROTTING—tho I do think it was probably too cold for that to happen! So now I only have one lettuce and two spinaches that haven’t put in an appearance yet—and four kinds of peas. I expect them all very quickly as soon as it warms up again.

Nothing to do with temps, but I’m running a "grand experiment" this year! I dug out a "trough" about 3" deep all the way down the rows for each lettuce and spinach, and filled them with mostly finished homegrown compost before planting the seed. Then I covered the seed (lightly) with more compost. I’m gonna see how much that helps with the IMMEDIATE bolting problem I’ve always had when they were planted directly in the BAD clay! It’s gonna be interesting, and, of course, I’ll be reporting back later!

Now—having given you all that wonderfully scientific method for deciding when to plant, I DO have another chart to link here! This is the one I’ve found most helpful in the past when I was getting "a feel" for what I should be putting in "when I had time!" I like this one because it gives you a range for how well the seeds germinate at different temps, so instead of looking for a certain specific temp—yeah! Like that’s gonna work at altitude!—you can get a "feel" for the general conditions they need! (Seems to me I may have gotten this link from somebody here on RMG! You, Digit?)

I’ve only ever actually measured the soil temps a couple times, and that was more out of curiosity than anything. Once you get down which seeds need cool/cold, and which need warm/hot, I think it really has more to do with GUT (and good luck!) than with a thermometer! Wing it! It usually works out! (Gotta get a "bird" reference in here somewhere!)

So for anybody who’s new to veggie gardening, I recommend the linked chart below to help you get your "feel" tuned up, and then just go for it!

Skybird