Dig anywhere in your yard and you'll likely turn up a shovelful of dirt, clods, rocks, roots, worms, half-decayed leaves and other materials. A lot of plants like this mixture, but sometimes you want a fine soil for growing seeds or carrots. Sifting the coarse matter out of the soil yourself is cheaper than buying bagged potting mix, and the materials needed to make a soil sifter are inexpensive.
A homemade topsoil screener allows dirt and small bits of organic matter to fall through the holes while holding back the unwanted stones and roots. The size of the mesh determines the coarseness of the resulting soil.
For screening small amounts of soil to cover extra fine seed, a kitchen colander or sieve could be used. Most screens, however, are designed to fit on a wheelbarrow. The simplest screen is a large piece of wire mesh placed on top, but many people prefer to make a frame out of lumber and attach the mesh to the frame. The wooden rim holds the soil as the gardener scrapes it across the mesh with a shovel or rake. The lumber may be joined with fine woodworking techniques or with metal braces. The mesh may be stapled on or attached with screws but it is advisable to make it easily replaceable if damaged.
A fine-textured mix is essential for covering small seeds and for growing vegetables such as parsnips or carrots whose roots become deformed in rocky soil. Invasive roots of plants such as quackgrass can also be sifted out of the soil. By sifting directly into a wheelbarrow, a gardener can minimize the effort needed to transport soil from one place to another.
The main consideration in making a soil sifter is the purpose of the sifting. If your intention is to cover small seeds, you will need a finer soil than if you are planting beets. If you want to grow carrots with straight roots, you will need to sift out large clods and stones, but a quarter-inch mesh will be sufficient. Removing invasive roots requires a smaller mesh than growing regular vegetables.
While there are good reasons for screening soil, beware of assuming that plants always grow better in smooth rather than stony soil. Many plants enjoy the aeration of coarse, rocky ground and will thrive in it. Fine soil may compact more easily, especially if stepped on when wet. Sift soil if you need to, but spare yourself the extra work if you don't.