Popular among home gardeners, raised beds deliver an aesthetic that planting into the ground can’t achieve. Some gardeners believe that raised beds can increase soil temperatures and extend the growing season.
Do raised garden beds stay warmer? Raised beds alone don’t cause drastic changes in soil temperature. There are several ways to increase soil temperature, and raised beds, in the right conditions, might help but do not deliver consistently warmer temperatures.
Gardeners are always looking for ways to increase production or maximize the beauty of their plants. Raised beds alone might not increase soil temperature much, but, when combined with other methods, increasing soil temperatures can deliver impressive benefits.
Benefits of Higher Soil Temperatures
Soil temperatures are the reason that farmers and gardeners plant things in different seasons. Some plants require high soil temperatures to germinate and flower, while others like cooler temperatures. High soil temperatures are beneficial, then, for only plants that require higher temperatures.
Raising the soil’s temperature in your garden, especially in spring, can help new seeds and sprouts grow into healthy, vibrant plants. Get a head start on your spring planting by increasing your soil temperature for seeding and sprouting new plants.
Some warm-weather plants, like tomatoes and cucumbers, will begin to seed, flower, and sprout sooner if you can maintain higher-than-normal soil temperatures. Gardeners and farmers know how important soil conditions are, and temperature plays a key role in your soil’s health.
Understanding Soil Temperatures
Have you ever left a chilly air-conditioned office to step into warm, bright sunlight? Imagine how nice that feels on your skin. Plants, of course, use energy from the sun to produce nutrition and grow, and lots of sunlight and higher soil temperatures can make sure plants are cozy.
Nutrients, moisture, bacteria, and other microorganisms, and soil aeration are factors in how well plants grow. Soil temperatures also affect plant growth; if it is too cold or too hot, plants won’t be healthy and might not grow at all.
The soil under the surface of the ground will usually be cooler than the air above-ground. The way that heat circulates through the atmosphere and soil are juxtaposed. During the day, sunlight warms the air above the ground, but only some heat is trapped in the soil.
The soil will usually heat to a few degrees lower than the air temperature, depending on how deep into the ground you are planting. According to thermodynamics, the soil will release some of the stored heat back up into the atmosphere at night.
Most natural soils will achieve peak temperatures at a depth of two inches and peak at about 30% lower temperatures than the air above the surface. At four inches below the surface, natural soils are typically 66% cooler than at the surface and only after hours of heat exposure, as the heat slowly filters down through the soil.
Do Raised Beds Stay Warmer?
The short answer is no, though it is logical to think that raised beds maintain increased soil temperatures. If you are raising soil out of the ground’s surface, that soil might get warmer faster and retain heat longer.
However, the reality is that soil in raised beds, without any other measures in place to retain heat, will act just like the soil on the ground. If you have two or four inches of natural soil in a raised bed, you can expect similar temperatures in the bed as the ground around it.
Why is it Unlikely?
Thermodynamics is beyond human control, but it is in the realm of human knowledge. Heat acts the same way no matter where the surface of the soil begins.
A raised bed of soil that sits atop more soil will retain and release heat, just like the natural soil around it. On the other hand, the mix of your soil will affect temperature. Natural soil, peat, perlite, and potting soil all have different heat-retaining attributes affecting the speed with which your raised bed warms up or loses heat.
Darker soils attract and retain more heat, and well-aerated soils will warm and cool more quickly. Soil mixes that retain a lot of moisture will heat more slowly, which could keep your soil temperatures lower than desired, but lose this heat much slower.
There are simply too many factors in play to determine that a raised bed alone will increase soil temperatures, but with clever engineering, it is possible to design a raised bed that will maintain higher-than-average soil temperatures.
Hügelbeet vs. Raised Beds
A Hügelbeet is another type of raised bed that you might consider for your garden, especially if you plan to plant vegetables and other produce.
What Is a Hügelbeet?
A Hügelbeet is an Eastern European and German gardening technique in which compost and wood debris are formed into a mound and used as a bed for planting. This sustainable method of planting forms a natural raised bed utilizing scraps that would otherwise be wasted.
While increasing soil fertility, improving drainage, and retaining moisture, a Hügelbeet makes it easy to garden in tight or suboptimal spaces.
How do They Compare?
A Hügelbeet, like a raised bed, will likely not maintain higher soil temperatures. Decomposing wood and compost releases energy into the soil but is unlikely to result in higher soil temperatures.
A raised bed is usually walled-in by wooden planks to hold soil rather than creating a mound of wood refuse and compost. A Hügelbeet is more sustainable and eco-conscious than a raised bed, but raised beds can provide an aesthetic quality that a mound of soil cannot.
Great Ways to Keep Your Garden Warm
Even though raised beds alone will not maintain higher-than-normal soil temperatures, don’t fret. There are still some great ways to keep your garden warm so that you can reap the benefits of higher soil temperatures.
The simplest way to maintain warm soil temperatures is lots of sunlight. Plant in a south-facing plot so that your garden will get as much sunlight as possible and avoid shaded spots. Increased exposure to sunlight will ensure that your soil stays warm.
Covering the ground below your garden with plastic or burlap will help the soil above the layer to retain more heat than average. The heat that the soil absorbs from the sun won’t be able to seep through the plastic as easily and will stay near the surface rather than filtering down.
When building a raised bed or even a Hügelbeet, a protective layer below the plot will give the gardener more control over the soil in general and has the added benefit of maintaining higher soil temperatures.
Start Plants Inside
Planting in a greenhouse or building a covering to go over young plants is also an excellent way to retain that hard-won warmth. You can start spring and summer plants inside, or, if that’s not an option, build a covering for the raised bed to use at night.
Planting inside will allow you to germinate and sprout seeds earlier in the season and increase your grow time and production. Covering the garden at night will stop the cooler night air from seeping the warmth from the soil that you worked hard to retain.
Building a removable “Greenhouse-cover” for your raised beds can also repurpose them early in the season to function as a cold frame.
As mentioned above, soil mixes and conditions can help keep your gardens warm. Tilling soil lightly before planting will aerate the soil, providing better drainage and encouraging warmer soil temperatures.
Some potting soils are darker than natural soils and bring the added benefit of extra nutrients. Darker soils will also attract and retain more warmth from sunlight.
Whether you are planting flowers for a display or sprouting and germinating tomatoes and other veggies, the soil temperature is crucial. Raised beds alone might not raise soil temperatures, but there are many ways for gardeners and farmers to ensure that their soil stays warm.