What is Topsoil?
Some people have the notion that topsoil is a
marvelous, naturally deposited material that contains
all the essential chemical, physical and biological
components necessary for growing beautiful plants.
Unfortunately, this is NOT always the case. Some
places sell topsoil that often needs amending with lime,
fertilizer or organic matter. Purchase from a well
known topsoil supplier like Peterborough Landscape
Use of topsoil is increasing in rapidly developing areas
where the native soil is predominantly clay. Concerns
have been raised about using clay- based soils for
landscaping or lawns. Questions frequently asked
1. When should topsoil be used?
2.What factors are important in selecting topsoil?
3. How can the quality of a topsoil be evaluated?
4. How does addition of topsoil affect drainage?
Deciding When to Use Topsoil
To use topsoil effectively, you must know two things:
what kind of soil you are amending and what kind of
result you hope to achieve. If your goal is to improve
drainage, your strategy will be different than if your
goal is to increase water-holding capacity. Applying
appropriate amendments can help alleviate either
In Peterborough, topsoil is often applied to “improve”
existing clay- based soils. The topsoil chosen for this
purpose is likely to be sandy. This scenario sets the
stage for increased nutrient deficiencies, acidity
problems and moisture stress. The very qualities of
sandy soils that improve drainage can trigger these
other problems. In such cases, the soil is better
amended with a combination of topsoil and organic
matter. Amendments that include compost, rotten
sawdust, manure, peat moss or aged tree bark can
improve drainage, soil porosity, nutrient retention and
soil pH. They can also increase biological activity and
promote root growth.
Your decision to apply topsoil will be based on the
qualities of the topsoil and the qualities of the soil you
want to amend.
Topsoil is commercially available either bagged or in
bulk. Bagged topsoil usually is sold in 40- to 50-lb
quantities and has been amended with lime, fertilizer
and organic matter. Bulk topsoil generally is a native
soil taken from the surface and sold in truckload lots.
Peterborough Landscape Supply topsoil, more than
meets the standards of a good topsoil.
The texture and fertility of bulk topsoils vary across
geographic regions. Sandy soils have physical
properties that make them easy to distribute, but they
have low nutrient- and water-holding capacity. As a
result, plants growing in these soils are more subject
to nutrient deficiency and drought stress. Sandy soils
generally require more frequent applications of lime
and fertilizer, particularly nitrogen, potassium and
sulfur. Addition of organic matter increases the water
and nutrient retention of these soils.
Typical soil test results from bulk and bagged
Topsoil HM% BS% pH P-I K-I Ca% Mg%
bulk 0.3 69 6.2 9 26 45 10.0
bagged 0.7 78 6.8
In contrast, clay soils aggregate and are hard to
distribute. However, they hold water and nutrients
quite well. As a result, lime and fertilizer applications
are needed less frequently than on sandy soils.
Evaluating Topsoil Quality
A soil test is the most reliable way to determine the
quality of topsoil. Typical test results from a bulk soil
and a bagged soil are given in Table 1. Most native
bulk soils tested have low pH and nutrient content,
both of which can be corrected with appropriate
amendments. The addition of amendments, such as
lime and fertilizer, also improves granulation of soil
particles. Keep in mind, however, that clays remain
clayey and sands remain sandy even after amendments
are applied. You can modify the chemistry of soils, but
their basic structure remains the same.
Optimizing Water Movement
The mechanics of water movement through soil is
often misunderstood. If a layer of sand is placed on top
of a clay-based soil, water moves readily through the
sand and is absorbed by the clay. In contrast,
if sand is placed below the clay, water moves into the
sandy layer only when the clay soil is totally saturated.
Therefore, placing a layer of sand on a poorly drained
clay-based soil has no effect on drainage of the clay.
Drainage of soils can be improved with any treatment
that enhances granulation or aggregation of soil
particles. Such treatments include lime, gypsum
(calcium sulfate), organic matter, sand or a
combination of all of the above. When adding topsoil
or other treatment to an existing soil, mix the two
thoroughly for best results.