Yesterday we talked about the containers.  Today we’re going to talk about the potting “soil” I’ll use when I repot my new babies.    It would be so easy if we just went to the store, picked up the one variety of potting mix they have, came home, transplanted our plants and they all lived happily ever after. 

But, it’s not quite that simple.   There are different choices of potting mixes and they really do serve different purposes.  African violet soil mix really is different from Cacti and Succulent mix.  And both of those are different still from an all-purpose mix. 

That said, potting mixes all should be designed to do three things:

1.       Hold moisture and nutrients around your plant’s roots;

2.       Provide enough air (yes, air) for growing roots to be able to breathe;

3.       Support the plant and anchor the roots.

Most potting mixes contain three main ingredients:  peat moss; ground bark and / or sawdust; perlite or vermiculite.  Some of them include some topsoil and others have slow – release fertilizers or moisture retention crystals added to them.   Cacti and succulent mixes should preferably contain sand and only small or no amounts of peat moss.

The peat moss helps the mix retain moisture, unless it is allowed to dry out completely.  Then, any water you add will simply stand on top of the soil or run down around the sides where the mix is shrunken away from the side of the pot.  As the water collects in the bottom of the container, the entire mass of potting mix / peat moss will begin to float.  You can deal with this by gently pushing the floating mass back into the water and holding it there until water moistens the peat moss, making it less buoyant again.  You can also place the entire container in a bucket of water, weight it down with small stones or pottery shards, and let it soak until the potting soil is re-hydrated, then remove the pot from the bucket and let it drain well.

Small quantities of ground bark and sawdust are added to potting mixes to improve drainage.  In larger quantities or with large pieces, it will reduce the moisture retaining capabilities of your potting mix, making it harder for your plants to thrive.    A “professional” potting mix usually is much finer and better blended than some of the home garden type mixes, but even the most expensive potting mixes sometimes have what seems to be the entire log lurking in them.  It’s best to pick these out and throw them away before you put the mix in your containers.

Perlite and vermiculite are minerals that are added to improve drainage and lighten the soil.  These are the little white or gray puff balls that you find in the mixture.  Vermiculite is mica particles and perlite’s base is volcanic glass.  Both are super-heated until they expand and pop like popcorn.  Vermiculite is better at retaining moisture than perlite but some gardeners are reluctant to use it, as mica is often found close to asbestos deposits and the vermiculite may contain small amounts of asbestos.

So, how do you know what’s in your ready-to-use soil mix?  Look for a list of contents on the bag to find peat moss or sphagnum peat moss, pine bark or other type of bark, and perlite or vermiculite as the primary ingredients.  If the bag doesn’t tell you, do the “feel and look” test.  Lift the bag and squeeze the mix inside.  If the bag is lightweight and the consistency is spongy or springy, that’s a good sign.  If the bag is very heavy or if when you squeeze the contents into a ball, it stays that way, it’s a bag to avoid.  Feel for the large pieces of bark or other clumps.

The best way to check your soil is to open the bag and inspect it.  Most retailers will not thank you for doing this, though.  But, if you do have a chance, sift through the mix and look for those “logs”.  Look also for the vermiculite or perlite balls and see if they are still intact or if they have been crushed.  If they are crushed, that is evidence of soil compaction and the soil has already lost some of its moisture retention and aeration capability.  If you pick up a handful of mix and squeeze it, when you open your hand, the ball of soil should crumble easily.  If it forms a ball that holds together, that won’t work well in containers.

Tomorrow we'll talk about one more thing you should do before you put that potting mix in your container.