If you’ve ever heard of a microclimate, you’ll probably understand that it generally refers to an area of land that has a different climate than the surrounding area. I have often visited the Vendée in France, which is in northwestern France on the Atlantic coast, but it has a Mediterranean climate, its own microclimate. You can also get a similar effect near a large lake where the lake will help cool the air or on a south facing slope of a valley side in the northern hemisphere as it gets much more sun than the north facing slope.
You can also get a similar effect in a much smaller space in your own backyard raised bed vegetable garden. If you built it near the wall of a house that faces south toward the sun (facing north in the southern hemisphere), this wall will radiate the stored heat, especially if it’s a brick or stone wall. The effect will not be as good with a wooden wall. If your raised bed garden is not close to the wall of your house, it is possible to recreate this effect using mirrors, although these are heavy and expensive. You can help combat this by using thin sheets of aluminum or something similar to ach as a mirror.
However, there is often no need to do something like this, as by planting your crops at a much higher density than normal using a method such as high density gardening, you can help create your own microclimate in such a space. small like 12 inches by 12 inches. Planting close together helps plants alter the temperature below them and helps conserve moisture, providing more shade for the soil mix.
When planting carrots, for example, the High Density Gardening eBook recommends spacing them 4 by 6 in a 12-inch by 12-inch mini-plot, and this close growing distance helps plants develop their microclimate beneath them. That gives you 24 plants from each mini plot. I have even planted carrots at a 6 by 6 spacing and have grown 36 plants in a mini plot. Guess what, I must have altered the microclimate around the crops as I got 36 carrots from them and routinely plant radishes in this space in my high density garden. It works and I guess a lot of it is because the plants alter the small space around them by creating a microclimate.