The main disadvantages of topsoil are that it can be difficult to predict its quality, it may contain pollutants and weed seeds, and it can be expensive. The quality of topsoil can vary greatly depending on the region and the supplier.
'Topsoil is rich in nutrients, making it the most fertile type of soil. It is generally used when establishing new gardens, lawns, or landscapes,' says Stephen Sullivan editor at the Plant Native. 'It is particularly beneficial in areas with poor soil quality,' he says.
Whereas topsoil is better suited for a wide range of projects, gardening soil usually fits more of a niche need, sometimes even plant-specific needs. Gardening soil is a combination of a mixture of soils and textures that is designed to target a specific type of gardening project.
For example, topsoil will be a better choice if you are filling a large land area. This is because it is relatively cheaper and will offer better coverage than lawn soil. In a smaller land area, lawn soil may be better because it is specifically designed to provide necessary nutrients to plants.
Landscape professionals often call topsoil fill dirt – but it's really not actual dirt. Dirt is what you find when you excavate a basement or attic. No plants thrive in dirt. Topsoil, on the other hand, contains natural organic matter from leaves, grasses, weeds and tree bark that can help sustain plant life.
Over time, mulch will break down and effectively become topsoil but it shouldn't be used in lieu of topsoil. That said, while you could leave your topsoil uncovered, it is wise to cover it with mulch to avoid erosion from the rain and overheating from our hot sun.
You certainly can use topsoil for potted plants, but that doesn't mean you should. If you do, your plant probably won't get the nutrients it needs, won't grow at the rate you expect and will be likely to die sooner. The best topsoil for vegetable gardens may not be topsoil at all.
If you're looking for a short answer, then yes, you can put topsoil over grass and existing garden lawns. Although it's possible for grass to grow through the topsoil, this can only be successful depending on the thickness of topsoil applied as a top dressing.
Rich topsoil is as beneficial for new grass as it is for old. Few people realize they can significantly boost the health of their lawn by carefully adding new topsoil. If you simply pile the soil on, you can kill the grass.
Soil Depth is Crucial
Topsoil is typically thought of as the top 6 inches of soil. We recommend adding at least 2 to 3+ inches of topsoil and rototilling it 2 to 3+ inches into the existing dirt to get the recommended 6 inches depth.
Triple mix soil generally consists of 1/3 soil, 1/3 peat moss and 1/3 compost. This triple mix combination is widely known as meeting most planting needs. Due to the moss and compost, it is more airy than regular topsoil, which is excellent for your plants – as it holds more air and water.
Good quality topsoil contains a rich mix of nutrients necessary for healthy plants. It appears darker than subsoil because of the organic matter it contains. The right type of topsoil retains water as well as nutrients, promoting healthy plant growth. A rich layer of quality topsoil ensures healthy lawns and gardens.
It's best to use it wherever you're lacking soil, for example, to fill in a low spot in your lawn, or as a base layer in a new garden that's missing a foundation of soil. If you use topsoil in a garden, you'd still have to add additional compost or manure to help your plants thrive.
Degraded soil makes growing food more difficult and expensive. Without healthy soil, farmers won't be able to grow nutrient-dense food to feed our growing population. The calculated loss in the region is part of a critical issue; some experts suspect that Earth will run out of usable topsoil within 60 years.
Incorporating topsoil into an area of lawn or a garden that tends to hold water improves the location's drainage. Use sandy topsoil combined with organic matter, such as compost or ground pine bark, and till it into the existing soil to a depth of 12 inches to create good drainage in the root zone area of plants.
Many think that putting topsoil over the seeds would protect it, but in fact, that will actually suffocate the seedlings rather than doing any good. We suggest that straw, hay, or any other type of mulching material be used.
Usually, 8 inches of topsoil is needed to fill a new garden bed or raised bed. If you intend to add topsoil to your lawn, you will need approximately 4-6 inches of topsoil to give you the healthy lawn you desire.
Topsoil Uses Can Include Fixing Uneven and Patchy Lawns
You may even notice areas of your yard that are slightly uneven. Topsoil is a great remedy for both problems. To grow grass, simply spread topsoil across the area so it is 1 inch deep. Evenly distribute grass seeds and till the soil to combine.
To start off you will need to clear the existing area before laying down your new soil. Then lightly turn over approximately the top 5 inches of the existing soil, this will loosen the ground and help make sure you get the best from your new topsoil.
Again, remember to mow the lawn the day prior to applying the top dressing; the longer the grass the more sandy loam or clean river sand required to cover the area and a deeper layer of soil will make it harder for the grass to grow through it.
(Grass and weeds will grow through soil 2 or 3 inches thick quite easily.) Once you add more than 3 or 4 inches of soil, the amount of weeds and grass that will grow through starts to drop off dramatically. This picture shows the new sod, old lawn, and the soil over top of the old lawn.
The most common use for bagged topsoil is a top-dressing on damaged areas of the lawn or garden. It typically contains little nutrient value but are a great filler or top-dressing.
For grass and most other plants, a medium loam, with proportions (by weight) of 40% sand, 40% silt, and 20% clay is the ideal growing material. That mix holds nutrients and moisture but lets excess water run through.
Tips on Storing Topsoil and Compost
For long term storage, compacting the top layer of the pile will help against erosion, though the use of a tarp is still recommended. Of course, the best option is to avoid the need for storage in the first place.