The Dirty Truth

We have been applying topsoil and triple mix to our yard every year. This year we are applying a little bit of a top dressing of soil and grass seeds over our lawn. We are also filling our raised vegetable garden beds with a mixture of soil. Each year we also apply a layer of mulch over our flower beds. These beds are on a steep slope which face quite a bit of erosion of the soil when the snow melts.

Setting up raised beds at the base of a steep slope

What is the difference between soil and dirt? I read somewhere that soil is the stuff in your garden while dirt is the stuff we have to clean up. I’ll worry about cleaning the dirt later, I just need more soil. Dirt and soil are all the same to me, but I thought it would be nice to lay out the facts about soil (or dirt).

Soil is a medium for growth of plants. It is more than just that – it contains minerals, sand, silt, clay and organic materials. Plants need enough weight to hold them down and support their stems, but their roots need air and water.


Clay is made up of very small particles which are compressed tightly together and so clay soil has poor air circulation around plant roots, but holds the water.


Grains of sand are larger and so water drains quickly from around plant roots, but minerals and nutrients also are depleted quickly from this soil.


Silt is granular, in between the particle sizes of sand and clay. It’s made up of quartz and feldspar. It holds the water well around the roots of plants but is not good for aeration.

PH in Soil

It is possible to have the pH level of your soil tested and to augment it if necessary. I don’t personally worry about this, unless I am having trouble with a particular plant. Soil is generally going to return to it’s original pH level over time, and so the augmentation must be ongoing. My soil is rich in compost and we just top up as often as we can! Plants require different pH levels. pH is a 14 point scale – from 0 to 14 where 7 is neutral and anything below 7 is acid, and anything above 7 is alkaline.

Blueberries for example like a soil of 4-4.5 pH – so acid! Evergreens, dogwood, magnolia, azalea, carrots, cauliflower, celery, cucumbers, garlic, sweet peppers, pumpkins, winter squash and tomatoes do well in mildly acidic soil. Composted fruit, composted pine needles and pine bark, elemental sulfur or a soil acidifier added to the soil will increase acidity.

Cabbage family plants, garlic and beets can tolerate mildly alkaline soil, as well as forsythia, weigela, watermelon and asparagus. Ash and lime added to soil increase alkalinity.

Soil Varieties:

Garden centres offer many types of soil and soil additives for sale – by the bag or in bulk.

Dry Topsoil

Black Soil

Black soil can be just any type of topsoil or triple mix. The key is that it is often labelled and priced higher than other soil mixes, when it may be the same soil for more money! Any soil CAN be black or dark. However, black or dark soil absorbs the sun and warms more quickly for spring planting and germination.

Photo by Lisa Fotios on


Topsoil is the top layer of soil. When a field, construction site or forest are cleared, the top layer of soil that is excavated is top soil. This soil is considered to be the best quality because it has the most organic matter from composting life forms. The quality of the site though will determine the amount of organic matter and texture in the soil. Generally, topsoil is screened to remove rocks.

Triple Mix

Triple mix is generally composed of 1/3 top soil, 1/3 peat and 1/3 compost. This definition and composition can vary – sometimes/often the compost is manure.


Compost is decomposed plant and animal material. It is generally a good source of fertilizer, and continues to decompose and release nutients into the soil. When we had room in our rural garden, we created our own compost in recycled plastic composters. We regularly added kitchen waste, grass clipping, leaves, occasionally wood ash and garden clippings, and pulled our compost out of the bottom of the bin. We have much less room in our current yard, but regularly take home free piles of compost from our local landfill. There is some ground wood fibres in this free compost, but it seems to give the soil a nice light texture.

Digging compost at my local landfill

Peat Moss

Peat Moss is available in large bales, and may be added to soil to lighten it’s texture. It creates air around the roots of plants and absorbs and holds water. It does not add many nutrients to the soil, but lowers the pH (addes acidity). I had noticed that Peat Moss was highly unpopular in UK gardening, but receives less bad press in Canada and was curious as to why.

Peat Moss is essentially dead sphagnum moss which is decomposing. Peat moss dies and forms deep bogs. As moss dies it forms very deep boggy areas full of the material, which is harvested and packaged into bags or large bails. Peat bogs develop over thousands of years and cover approximatedly 3% of the earth’s surface, with Finland leading the way, followed by Canada, Ireland and Sweden.

Photo by Lukas on

Peat bogs are wetlands or ecosystems which naturally purify water. They contain unique wildlife, and native plants which may be threatened by harvesting of peat. The acidic ecosystem results in a very slow decay and unique species. They filter and estimated 10%of the world’s freshwater, and are important in flood prevention. When peat bogs are harvested, trenches are created to drain the water. This can effect local waterways and drainage patterns.

It is theorized that peat bogs help prevent climate change by cooling the earth. Vast bogs of living sphagnum moss absorbs carbon dioxide. It is believed that the carbon dioxide is then contained in the peat (decaying sphagnum moss). In theory, if the peat is harvested it could release carbon dioxide back into the atmosphere.

In the U.K. it is estimated that heavy industrial pollution is stored in the peat bogs, and that if they are harvested and the bogs are dried out, this carbon will be released into the atmosphere. The government is tasked with preserving the country’s peat bogs. In Canada, bogs are required to be returned to functioning wetlands after the peat has been harvested. Canadian peat producers log the wildlife and plant material before the harvest, harvest only part of the bog, leave a layer of peat in hte bog and restore the water table after production.

Potting Soil

Potting is another mixture of soil – and can generally be top soil with peat moss, but might also contain perlite and or vermiculite. These minerals and peat moss, lighten the texture of the soil, making it easy to work with in pots.


Perlite is a volcanic glass with  a relatively high water content which expands when heated.


Vermiculite is produced by the weathering or water and heat treatment of the minerals biotite and phlogopite (mica). It is light like perlite and also expands when heated. Pure vermiculite does not contain asbestos, but it had been associated with asbestos contamination until the early 1990s. Vermiculite mines are now regularly tested for asbestos and are supposed to sell products free of asbestos.

The dirty truth is that we can only guess what’s in our soil based upon how it looks and what’s on the label. You can’t beat well drained dark soil with lots of compost though!

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