Topsoil or Compost: What’s Best for a New Lawn & Why? (Answered!)

From preparing the soil to choosing which seed to buy, laying a new lawn is a daunting undertaking fraught with perils of every description.

We are going to try – in the broadest possible strokes – to take the sting out of this endeavor so that you can proceed knowing that you’re following acknowledged best practices.

First of all, let’s dispel the notion that there is a choice to be made. It’s not a question of compost or topsoil. Both are necessary.

How and when to use and combine them, are the decisions that need to be made.

Laying the Foundation for the Best Possible Outcome

To start out with, take a good, long look at the patch of ground you’re planning to transform.

Where are the holes or areas where the ground has subsided or where it is particularly uneven? These are the spots you want to level off with topsoil.

Now turn your attention to the weeds. Where are they growing? Where are they not growing?

It’s safe to assume that the soil is fine in the places where the weeds are thickest. The spots where hardly anything is growing, that’s where you want to spread compost.

But now it’s time for some soil analysis:

The Benefits of Getting Your Hands Dirty

You don’t need a Ph.D. in agronomy to analyze your soil. Your eyes are all the diagnostic aids you need.

Two basic tests will determine your soil type. They are the Squash Test and the Jar Test. They are very straightforward and take hardly any time at all:

The Squash Test (a Quick Test!)

Dig a small round hole six inches wide and six inches deep. Take a big handful of soil from the bottom of this hole and squeeze it into a ball. Now open your hand.

A soil analysis video using the Squash Method comes to us courtesy of the Central West Local Land Services in Australia.

Now for the fun part…

The Jar Test

Remove any stones and vegetable matter from the soil you dug up and place the soil in a glass jar. Fill it up most of the way with water, screw on the lid, and shake it hard for a good couple of minutes until all the soil particles are floating in suspension with nothing resting on the bottom. Now let the jar stand for three or four days. (The longer the jar stands, the more accurate your results!)

When you come back, the soil will have settled to the bottom, with one important difference: now it’s organized into three distinct layers, each with its own texture and color.

The bottom layer is sand, the heaviest. The middle layer is silt. The top layer is clay, the lightest.

Measuring the Jar

Now, by measuring the thickness of each layer, you can calculate what percentage it is of the overall sample.

If the overall sample is four inches deep and the sand layer is one and a half inches thick then one and a half times one hundred divided by four is equal to thirty-seven point five percent.

If the top, clay layer is two inches thick then two times one hundred divided by four is equal to fifty percent.

You don’t even have to measure the silt layer: one hundred minus fifty minus thirty-seven point five is equal to twenty-two point five percent.

So now you know that your soil is half clay with a big chunk of sand and some silt making up the difference.

If there is a layer of organic matter floating on top of the water, this could be peat: a possible indicator of acidity. If there is a thin layer of white crystals at the very bottom, this could be chalk: a possible indicator of alkalinity.

A video, ‘How To Determine Soil Type Using The Jar Test Method’ is good to check out.

More About Soil

There! That was fun, wasn’t it? :) A bit like the science projects we used to do in junior school.

If that has piqued your interest and you’d like to learn about soil testing in greater depth, you might want to visit ‘10 Easy Soil Tests – How to Test Your Garden Soil” from the good people over at Good Housekeeping. It can be found here.

There is also a video about the different soil types produced by the folks at the Royal Horticultural Society:

Now that you know your soil type, you might want to start thinking about which variety of grass you want to grow. See ‘Types of Grass Seed: How to Choose the Right One’.

If you live in a drought-prone region with hot, dry summers, combining strains of drought-resistant grass can ensure you have a green lawn without having to use excessive amounts of water.

Soil Types

Make no mistake!

Understanding soil types saves you money and gives better results!

Clay Soils

Clay soils are heavy and compact. They retain more water than other soil types and don’t drain well, so they’re inclined to become waterlogged. On the upside, their density means they’re better at retaining nutrients.

The more clay there is in your soil, the more compost it needs. Leaf compost is best. It contains high levels of humus, the organic material formed from decayed plant and animal matter. Leaf compost is also exceptionally absorbent. It retains water well, a Godsend in Summer when clay soils tend to become super-dry!

Another advantage to leaf compost is its ability to reverse compaction when soil becomes so dense that it inhibits root growth and development.

Sandy Soils

Predominantly sandy soils require a bit more than just compost. The regular application of a slow-release, granular fertilizer is called for since sandy soils are an epic fail when it comes to retaining nutrients.

For a detailed breakdown of lawn fertilizers, follow that link.

A thin layer of mulch – light organic material like chopped leaves, grass clippings, wood chips, and shredded bark – can help with water loss by reducing evaporation.

Silt Soils

Silt soils are a mixture of sand and clay. They are the most conducive to plant growth. It’s both dry and soft, which means that as well as retaining both moisture and nutrients, it has good airflow, allowing oxygen to more readily reach the roots!

Its pH value (acid versus alkali) is nutrient- and earthworm-friendly!

Last but not least, its calcium levels tend to be higher than that of other soil types. Calcium (in case you didn’t know) maintains the balance of soil chemicals, breaks up compacted soil, and reduces the salt content!

Buying the Right Topsoil

By now you will have realized that there are different kinds of topsoil just as there are different kinds of compost.

When laying a new lawn, general-purpose topsoil is best.

General-purpose topsoil comes in different grades, from coarse to fine. The finer grades are used more for top dressing. Coarser grades are cheaper and fine for lawns, but they shouldn’t be completely ungraded. Too much debris can cause root rot.

It’s worthwhile bearing in mind at this point that the sale of topsoil isn’t regulated. There is no industry standard. It’s a case of caveat emptor – let the buyer beware! In other words, it’s up to you to ensure the quality of the product you’re about to purchase!

The best way of doing this is by taking a close look at it and by touching it to feel its texture.

Quality topsoil is a mixture of compost, organic matter, sand, and clay. It’s relatively clean in that there aren’t too many stones and twigs, and the overall amount of debris is minimal.

High-quality topsoil should crumble easily and feel slightly gritty. The loose texture is a sign that it’s rich in organic matter.

Topsoil: How Not to Get Ripped Off!

If you live in the suburbs, chances are topsoil and compost comes in bags, not in their raw state. How then to evaluate it, when you can’t even see it, let alone touch it?

Simple! Buy one (and only one) of the smallest bags on offer. Once it’s yours, you can do with it what you will.

This applies to compost as well as topsoil.

By the way, store-bought topsoil tends to fall into three categories: premium, general-purpose, and economy.

Premium is the most expensive. In return, you get a nutrient-rich, weed-free mix with a good, loamy structure ideally suited to growing flowers. Best practice from an economy point-of-view? Stick to general-purpose?

Buying the Right Compost

In their Organic Lawn Care Guide, North Carolina State University lists the advantages of compost over topsoil as follows:

Compost: How Not to Get Ripped Off!

The compost should contain controlled ingredients free of persistent herbicides that create killer compost.

For the sake of the environment, it should be peat-free.

It should be dark like chocolate cake mix, with a smooth consistency, and feel great in your hands.

Again, if you don’t have access to the raw product, buy one small bag and examine that first.

Compost Versus Fertilizer

Fertilizer is great in a pinch or when you need to give your lawn an extra boost. Unfortunately, it does nothing for the structure of the soil. It won’t break up compacted ground, assist drainage, or improve aeration.

Last but Not Least

Visit Yardthyme’s ‘Ultimate Lawn Care Calendar’ for a step-by-step year-round guide to lawn care.

FAQ

Can I mix compost and topsoil together?

For those reasons, it’s best to use compost mixed with topsoil to create an optimal and sustainable environment for your plants, and then add in fertilizer should you need it.

This could be to amend specific nutrient deficiencies or to give veggies a boost during their growing season, for instance.

Is compost cheaper than topsoil?

No. Compost is more expensive.

Can you add too much compost to the soil?

Yes. Compost tends to dry out faster than topsoil. In any mix, topsoil should predominate.

Can compost burn your lawn?

Yes. More than an inch or two is too much! Anything in excess becomes toxic.

How much compost do I add to my lawn?

After the lawn has been planted, the most effective method for applying compost is to mix it with water and sprinkle it on the grass with a watering can.

Can you use compost and fertilizer together?

Yes, this is fine.

How long does compost last in soil?

As long as it takes to be fully absorbed into the ground, depending on the type of soil.

Research Pays Off!

A little bit of homework goes a long way! Educate yourself before committing to a long-term strategy and you can’t go wrong.

Your comments, feedback, general remarks, and criticism are roundly welcomed and eagerly anticipated! If you have anything you’d wish to add, that you feel we left out, please don’t hesitate to get in touch.