January 20, 2020

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.

Selecting Topsoil

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.




Posted In: Top Soil
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