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page 2 title pg


This is page 2 of the series on medium. We will explore the different components you are likely to find in your local garden center and some reasons to choose them.

by Mary Sue

     Here’s The Dirt…page 2


          Time to explore and get your hands dirty



When you know the needs of your plant you can combine any number of ingredients to create a perfect habitat or there are many commercial potting mediums based on the following components.  The ingredients you supply to your plant will dictate your plants growth.  Garden soil alone is unsuitable for containers because it may contain weed seeds, pests and diseases.  The drainage often becomes poor quickly without the activity of worms and other animals once you put it into a pot and place it indoors.  Finding materials to mix together to create the best environment for your houseplants has never been easier.  We will begin by exploring the many ingredients you can use in many combinations to create many different habitats.

Basic Ingredients


– contains the following 3 ingredients mixed in relatively equal amounts.  The clay and silt hold moisture and nutrients and the sand keeps it from becoming compacted.  Loam will crumble in your hand yet hold its shape.  It will not dry out in the summer too quickly or get water logged in the winter.

Sand – large particles allowing aeration and improving drainage but does not hold nutrients well

Silt – medium particles that contain moisture and hold onto it, but can become compacted

Clay – small particles that pack down so water cannot flow through easily and air cannot circulate but has the ability to hold onto any nutrients supplied and will resist acidity change

sphagnum peat

sphagnum peat


– is still breaking down. Sphagnum peat is humus but so very broken down that very few nutrients remain and is beneficial in providing a nearly constant acidity (slightly rising as time passes) that will hold water like a sponge.  It is usually free from weed seeds and disease organisms.  It is a good substitute for leaf mold if not available but will be without the nutrient and bacterial value of the leaf mold.  Used to provide aeration, water retention and anchorage.  When using in a mix, dolomite limestone may be added to help neutralize the acidity.  A bonus quality is its ability to suppress fungal disease that can cause root rot.  When using in a mixture for a plant that likes a more moist soil it can be very beneficial.  Be sure to moisten it before adding it to your mixture or before adding your plant to it and never let it dry out completely as it can be very difficult to re-wet.  It is harvested mainly in Canada and Europe and does involve destruction of the natural habitat of many plants and animals.


– from sedges, is not as uniform as sphagnum peat moss and its acidity is various.  Used to provide water retention and aeration outdoors but not usually suitable for container, houseplant gardening.  It has short fibers and can compact too tightly around roots.  Look for the word sphagnum when choosing peat for your houseplants.


– a good coir mix, made from ground coconut husk, will contain both the pith, fiber and chips.  Often used as a substitute for sphagnum peat moss for the environmentally conscious.  Will retain water well and supply the same aeration as a coarse sphagnum peat.  Mexican coir, readily available, is essentially free of sodium, is rich in potassium, has some anti-fungal properties and has a stable ph of about 5.98, slightly acidic, depending on the grade.


– organic matter that is still breaking down, supplying nutrients, aeration and will hold moisture.   Any of the following 3 ingredients can be added to a nice sterilized loam to provide the necessary food and aeration for most houseplants.  It would be an excellent top dressing to freshen the medium of an established plant when not re-potting.

Composted animal manure – well-rotted manure is valuable as a soil conditioner, adds nitrogen and has a high population of good bacteria.

Decaying leaf mold – partially decomposed matter from the forest floor and is an excellent compost that is rich in bacterial life and organic fertilizer and should be used when flaky not powdery.

If making it yourself from yard leaves (high carbon material), you need to add a source of nitrogen (green stuff like grass clippings, flowers, coffee grounds or fruit and vegetable scraps), keep it moist (like a damp sponge) and turn it to aerate (perhaps twice a week).  This will get the bacteria working that turns it into a nice compost that will supply nitrogen and beneficial microorganisms to your plant.

Decaying bark – partially decomposed from the bark of a pine or other, usually a hardwood, tree.  Contains anti-fungal properties and can help prevent soil-borne disease like root and crown rot.





– decomposed plant and animal matter.  It can enrich the soil with minerals, nutrients, raise the water-holding capacity or increase porosity and aeration depending on the source.  Mixing it with a clay soil may allow more air to circulate, mixing with a sandy soil may allow more moisture to be retained.  Mixing with anything will create an environment that stimulates the development of micro-organisms you need in a healthy soil.  It is generally well-decomposed, perhaps from lake bottoms and can be aerated with a larger particle matter, to make it more suitable for your plants, such as a coarse sand, pine bark fines, granite chips, sphagnum peat moss (or coir which is replacing sphagnum peat for the more environmentally conscious). Humus from peat sedge may be too fine for container gardening and will pack too tightly around roots.  Know what the humus comes from.




– made from heated volcanic rock.  Heating expands it and makes it lightweight and crunchy.  Approximate neutral ph 7.0.  Provides aeration, water and some nutrient retention from fertilizers, will not break down (unless you crush it), and is lightweight for containers.  May want to add dolomite limestone when using to neutralize the notably high fluoride content so your plant will not be able to absorb it.





made from expanded mica.  Used to aerate a medium – perhaps a bit less than perlite, helps retain moisture and nutrients – perhaps a bit more than perlite and has minimal nutrient value of its own.  It will compact over time.  Ph can vary from 6 to 9.5.




builders sand

builders sand


– coarse builder’s sand is used to improve drainage and add weight to a container.  It has no nutrient holding value.  Be sure it comes from rivers or fresh water lakes as you do not want added salt.





– larger particles than coarse sand (3/16”-5/16”) but still small and can be used in place of sand, must be washed to remove dust.  Used to provide aeration and weight.


– a clay pebble, comes in several sizes, has been heated to create a porous medium.  Used to provide support and aeration, often in bonsai and orchid mixes. Holds moisture, with ph 7.0.  Sold under the names Aliflor, or Turface, etc.  Use a screen to sift out some of the more fine bits and rinse to remove dust before using.

medium size fir bark

medium size fir bark


– use pine, fir, cedar, or hemlock bark all under the size of a dime, smaller bits are good.  Used to aerate the medium and supply nutrients and minerals.


– Hardwoods decompose more slowly.  Abies concolor (a N. American evergreen fir tree) is commercially available for Orchids and Anthurium.  Available in chunks also.


– reduces acidity and supplies calcium and magnesium.  A coarse limestone is preferable to a finer grade because it will release nutrients more slowly.


– contains over 70 minerals and can be used to fertilize and aerate soil mixes.  Use ¼ pound per 1 cubic ft. of medium or 1-2 t. as a side dressing of established plants.

sphagnum peat, perlite, vermiculite and sand.

sphagnum peat, perlite, vermiculite and sand.

moistened and ready - perhaps for a succulent

moistened and ready – perhaps for a succulent

When you have chosen your ingredients, added them to your container and mixed them well it is a good time to moisten it all and give it another stir.  There will be less stress on your plant when you give it the new home if it does not have to search for water.         Soil Recipes


There are many commercial mixes you can purchase for nearly any type of plant and with the guide above you will be able to decide if they are right for your plant or if you would like to enhance one you bring home with any of these ingredients to get to the proper habitat you feel your plant needs to be a happy, healthy grower.

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