Fertilizing 101, part 2: soils

I started to write this blog and quickly realized it would be waaay too long if I write about both soil and fertilizer. So this one will be an introduction to soils and what makes a good soil.

The backbone of a healthy and productive garden is the soil.  It both supports and feeds the plants that grow in it.  By far the best way to create a happy healthy garden is to build and prepare the soil before planting.  Like I always say about watering systems, install them before the plants.  Its a lot easier to bring in good soil before the plants than trying to add it after.  Vegetable garden soil can be amended after all the veggies are done and pulled but permanent perennial and shrub borders are much more difficult to work in without damaging roots once the plants are mature.


Hellstrip soil.  Note the clumps of clay that turn rock hard in the baking sun

Soil is a mixture of mineral matter: sand, silt, clay; organic matter such as decaying plant matter and animal waste; and living organisms.  Soil organisms include macro-organisms like small mammals, worm and insects (both good and bad!); and micro-organisms like nematodes, protozoa and bacteria.  Plant organisms include roots, algae and fungi.

The diagram below is known a the soil texture triangle and shows the various soil types depending on percentages of sand, silt and clay. Ideally your soil should be in the loam category with lots of organic matter.  Too sandy and the water runs through too quickly taking nutrients with it.  Too much silt or clay and the water either sits in the soil and the roots drown or the soil becomes so compacted that water or air can’t even penetrate and the plants die.


Sand creates stable pore spaces to allow for good aeration and enough silt/clay makes sure the water doesn’t drain too quickly.  The uniform grains of sand touch each other to create large open pores that withstand heavy foot traffic and watering.


Compacted soil won’t leave a footprint when you walk on it

Finer silt/clay particles lock together and fragile organic matter breaks down into finer components and both compact quickly under pressure.  That is why a good soil has a balance of sand, silt/clay and lots of organic matter.


The soil in my rose bed:  rich, dark and full of organic matter.  I do pick out the diseased leaves though!

You can always have your soil tested for texture, ph, nutrients etc. but there are a few easy DIY tips.  First look at your soil.  It should be dark coloured with a sweet, fresh yet earthy smell, not smelly!  You may find an earthworm or two and hopefully only the occasional grub!  If it stinks, air is not getting in, the micro-organisms are decomposing the organic matter without oxygen and creating gases like sulphur and methane.  Moisten the soil and form it into a ball in your hands.  It should hold its shape without compacting or falling apart.  If it falls apart you have too much sand or coarse matter and need to add organic matter and some silt.


Sandy stony soil, lighter in colour and drains very quickly

If it compacts into a ball like play dough then you have too much clay and need to add some sand and of course organic matter.  When you buy topsoil, get it from a reputable dealer and make sure it is balanced and certified weed free or your gardening life will be hell next season!  You basically get what you pay for 🙂


Purchased topsoil/container soil with added perlite

Existing soil structures can be improved by adding organic matter such as compost, manures, peat moss, spent plant material, green crops and inorganic matter such as perlite and vermiculite, and even fine gravel for scree, cacti and alpine gardens.  Manures and green crops are generally used on an agricultural scale in the fall.

Organic matter should be added yearly as it is pulled down into the soil and broken down continuously by earthworms and soil micro-organisms.  A great free source is of course the leaves that fall every year.  Just make sure to grind them up first in a leaf mulcher or lawnmower before adding them to the garden.  Large leaves tend to become soggy and mat down, potentially rotting your precious perennials and causing mold growth over the winter.  A mulching mower is great for chopping up both grass and leaves.


Lovely homemade compost with lots of organic matter and earthworms.  There’s one in the middle of the photo!

A good soil base creates a healthy ecosystem both below and above ground.  It reduces the amount of fertilizer you have to add, saving you time and money and is of course good for the environment.  But plants are living beings and need to be fed like us and that is where fertilizers come into play.

Next time, fertilizers and how to use them.

Happy gardening!




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