Soil Temperature: What It Is And Why It Matters

On any given day, normal people are concerned with the temperature of the air. If you have to walk a few blocks to the subway, or you want to plan a barbecue, the ambient air temperature can affect whether you go out in a t-shirt or hunker down inside. But us gardening folk are a little different from the normies.

我们不仅关心空气温度，也关心土壤温度。We may even obsess about it, particularly when winter runs its course, and our green thumbs get to itching.

土壤温度可以决定种植的成败。它是西红柿从微小的种子中生长出来的关键，也是防风草生长出美味的甜味的关键。它可能是我们最大的资产，也可能是最严重的祸根，这取决于我们想在花园里种什么。了解土壤温度以及如何处理它是管理你的农田的一个重要部分。

Soil Temperature Versus Air Temperature

土壤温度和空气温度一样，都是花园规划的一个要素——尽管你不会在天气频道上听到它。然而，对于一个园丁来说，了解土壤温度的每日波动是在春季和秋季气温变化很大的季节里园艺成功的关键。

The top 6 inches of soil is probably the most important to a gardener. It is where the majority of your plants will be sown, grown, and harvested. Much like the air, the soil has daily highs and lows, but they act somewhat independently of the surface temperature. If you’ve ever been in a root cellar, you’re familiar with the insulative power of earth.

Your garden is similar. The soil will retain heat longer than the air does during some parts of the year, whereas in other seasons, it will stay frozen even if the air feels positively balmy. Being able to understand and work with these seasonal changes will help you advance your garden game from newbie gardener to an experienced green thumb.

How To Measure Soil Temperature

找到表层土壤的温度就像使用土壤温度计一样简单——一个你可以在网上商店或园艺中心找到的工具。然而，不要随意地把这种相当昂贵的设备塞进土壤里。先用螺丝刀打一个导孔，这将有助于在未来几年保护温度计的探头。

然后，根据你使用的温度计的类型，给它几分钟的时间来获得准确的读数。你知道你得耐心等待你的第一个番茄。当然，你可以等待几分钟，让温度计完全记录温度。

The thermometer should take a reading that is around 5 to 6-inches deep. The visible surface of the soil will sometimes be drastically different than the actual soil around your (hopefully) germinating seeds, so that depth is important. Also, make sure you shade the tool with your hand as you take a reading. Bright sunlight could accidentally mess with your results.

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Finally, take several readings around the garden. The part shaded by the big oak tree may take longer to warm up in the spring than the area in direct sunlight, so plan your plantings accordingly. Also, take measurements in the morning to get the lows and measurements in the late afternoon to determine your soil’s highs.

The average of these numbers should give you a temperature for deciding what’s going in the garden next. Bear in mind, however, if temperatures are too cold at night, sensitive seeds like tomatoes and eggplants may not germinate even if the average is ideal.

If you keep a garden record book or journal (a recommended activity), jot down the values you get along with the date. Though the seasonal soil temperature of your USDA growing zone is somewhat predictable, the actual conditions of your garden’s specific microclimate may be different enough to make an impact.

Knowing the history of how your property warms or cools will give you the heads-up if there’s a warmer or cooler-than-usual year, and hopefully, spare you some unnecessary frustration.

What’s The Optimal Temperature For Planting Vegetables?

Seeds can be tricky little stinkers. While an established plant can sometimes handle a cold snap or heatwave with little damage, germinating sprouts are much more finicky. The majority of leafy greens prefer cooler temperatures and either won’t germinate if it’s too hot or will bolt almost immediately. Lots of annual garden crops, however, prefer it warmer and won’t germinate if it’s too cold.

The cold and wet of early spring can often rot seeds that are sluggish to germinate, making you wish you’d waited. Don’t let the array of uncontrollable factors make your head spin, though. The balancing act of seeds, soil, and timing is an art form that takes a lifetime to master and enjoy. Just learn from every success and failure, and make the necessary changes next year.

Some gardeners overcome the needy baby stage of their garden by starting seeds indoors under ideal circumstances. Once the seedlings have been hardened, they can be transplanted when the weather outside and the soil temperature are milder.

决定何时移植是每个园丁不得不冒的一个更大的风险。一旦土壤变暖，我更喜欢直接播种，但生活在6区气候确实给了我更长的生长机会，以弥补任何延迟。

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Here’s the general range for some common vegetables, taken from one of my favorite organic gardening books,Burpee’s The Complete Vegetable & Herb Gardener. Note the range for successful germination is pretty wide with every category, but a plant does have a smaller, ideal range, usually printed on its seed packet.

Additionally, some cultivars of crops have been specifically bred to handle higher or lower temperatures than their counterparts, so don’t despair if your climate isn’t ideal for your favorite vegetables. Maybe the right variety is still out there, and waiting for you to plant it in climatically correct success.

• 50-85 degrees Fahrenheit: Beet, cabbage, carrot, cauliflower, celery, Swiss chard, lettuce, onions, parsley, parsnip, peas, radish, spinach
• 60-85 degrees Fahrenheit: Asparagus, some bean varieties, celery, corn, cucumbers, tomatoes
• 70-85 degrees Fahrenheit: Lima beans, okra, pumpkins, watermelons, peppers
• 80-95 degrees Fahrenheit: Eggplant, melons

My final advice for direct sowing or transplanting seedlings is to not rush things with your enthusiasm for getting back into the spring garden. Take a lesson from my first year of planting okra. My planting of the round, pearly seeds was at the very brink of their cold-tolerance early in the year. I had a pathetic 20% germination rate, and those that did break ground grew at a snail’s pace.

Taking a cue from my sad results, I waited a month and replanted. The second planting of okra had ideal warm soil, germinated in a fraction of the time, and grew with so much vigor it was astounding. The second generation of okra grew taller than my clothesline and produced pods like mad.

Those earlier survivors of my overambition never grew past my waist and made a total of four pods each. You could hear a sad violin playing in the background whenever you looked at them.

我们从中得到的教训是，即使一颗种子能够发芽，也并不意味着它一定应该发芽。让植物在理想的土壤温度下入土——即使这意味着要等待一个月——会给它们一个更强壮的开始，让它们生长得更有活力。这足以弥补你在等待中损失的时间。

How To Manipulate Soil Temperature

There are many strategies for working with soil temperature to make it more appropriate for your designs. Of course, unless you live in some sort of bio-dome, there’s no fighting the weather or changing the reality that exists outside your window. The following methods may help you achieve your planting goals faster, extend the harvest, or protect your seedling garden in the event of extreme weather shifts.

Your growing zone will determine how drastic the measures you need to take — southern growers past zone 6 may benefit from little more than thoughtful management of mulch or cold frames. Northern growers may need to employ a whole host of covered tunnels and greenhouses to help their plants produce through the extremes of their climate.

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I highly recommendEliot Coleman’s book Four-Season Harvest适合任何种植者，特别是2号到5号种植区的种植者。他在缅因州的花园一年四季都非常高产。如果他能在二月中旬挑选一份新鲜的沙拉，做一份刚刚收获的烤根茎蔬菜汤，那么你也可以!他关于冷框架的构造和使用的文章对冬季园丁特别有见地。

Utilizing Southern Slopes And Ados

If you live in the northern hemisphere, simply placing your garden on a south-facing slope can warm the soil considerably faster than the north-facing alternative. Watch your land in the winter. The snow on southern slopes will always melt first.

If you live on flat land, however, you can purposely slope the soil in your garden in a southerly orientation to take advantage of the sun’s winter angle. This is called ados in France, and there’s usually a slope that’s 4 inches of rise for every foot of garden (a 15-degree angle). You can add a bonus to the warming effect by placing these sloped garden beds against a stone or brick wall. The wall will absorb the day’s heat and help warm the ground through the cold of the night.

Applying Mulch

This thick blanket of organic material can both warm or cool the soil, depending on the conditions of your garden. Mulching seedlings too soon in the spring will slow the soil’s ability to warm with the growing daylight hours. This same insulative protection, however, can protect plants during the worst of summer’s blazing heat by helping retain the morning’s cool soil moisture throughout the day.

By the same token, a thick layer ofmulch in the fallcan retain the soil’s warmth longer, and allow you to extend your fall harvest until the first killing frost. Even then, massive amounts of mulch applied over “heeled-in” vegetables can turn your garden into an outside larder, allowing you to successfully dig up cabbages, carrots, and parsnips in the middle of a blizzard.

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Plastic coverings are also used as mulch, but I always feel funny recommending any single-use plastic product. When organic material does the same job while simultaneously enriching the soil and not contributing to any landfill, the short-term convenience of plastic mulch seems wasteful in comparison.

Cold Frames

These simple tools can be immensely helpful moderating soil temperature. They are essentially, bottomless glass-covered boxes placed over a space in the garden. The boxes can make the climate inside as much as 20 degrees warmer on a bright day, though a difference of 10 degrees is more typical.

With some careful venting during sunny days, these frames make it possible to harvest frost-free food year-round. The best part? They are easily made from recycled materials — an old window mounted on some scrap wood serves the purpose as well as a store-bought model.

Soil Solarization

有时候，让土壤变暖不仅仅是为了帮助植物。如果你发现你的菜园面临着巨大的问题，比如难以克服的越冬害虫，或真菌来源的枯萎病，在你收获番茄之前偷走了每一个番茄，那么对土壤进行日光照射是一个让你的菜园重新开始的自然方法。

This process takes place during the hottest part of your summer — either July or August in the northern hemisphere — and involves covering selected areas of cleared, watered garden beds with a close layer of plastic. Left in place for at least six weeks, this super-intense covering will heat the top 6 inches of soil to deadly levels (around 150 degrees Fahrenheit). Unless you take a summer gardening pause for the treatment, you’ll have to treat the garden in sections.

High Tunnels And Greenhouses

Of course, to really fight the wild variations in your climate, you can install structures like high tunnels or a greenhouse. These require ample space in many circumstances, so they’re probably more functional on a homestead than a suburban backyard.

Gardeners have been both fighting and embracing the soil temperature of their cultivated plot for generations. These methods are merely a selection of the many ideas out there. From cloches to chenilles to low tunnels to buried greenhouses (yes, that’s a thing), there are many more ways to both understand and manipulate growing conditions. So what have you done to measure your soil temperature, and how do you manage it? Let me know in the comments below!