Container Gardening - Using the Right Soil

Succulent Dish Garden (Wiese Acres photo)

Well prepared garden soil is great - if you are growing plants in a garden.  In a container?  Not so much. 

Soil in containers becomes compacted much more easily than in large garden beds.  Potted soil needs to be well-aerated and well drained, but still hold adequate moisture to support the moisture needs of the containerized plants.  Garden soil just won't do that for you.

Most potting soils are actually soilless mixes of peat moss, finely shredded bark, and vermiculite or perlite.  These work for the majority of plants, however, for succulents, you may want to change to a soil with less or no peat and more perlite or vermiculite.  It might be ok to add a little bit of sand to the potting mix for succulents, but be cautious. Sand adds a fair amount of weight to the mix and could potentially crush the more tender roots of your plants.  Tropicals or bog plants may be happier in a soilless mix that contains more peat moss that will retain moisture more aggressively.



WieseAcres Containers

Fill the pot to within about an inch from the top and moisten the potting mix before planting.  Leaving that inch of head space makes it easier to water without having your soil bubble over the top each time you water.  It also allows for a "collection basin" for the water as it drains through and moistens the soil below the surface.  Moistening the potting mix and allowing it to settle before planting allows you to make sure that one inch of head space stays at one inch.  The drier your planting medium is when you fill the pot, the more it is going to settle when you moisten it, and you may need to add to the top to keep the soil surface from being way down from the top edge of the container.

Potting mix can be expensive and larger containers can take a lot of it. I don't replace my potting soil in my containers every year.  If I had disease problems with any of the plants, I will discard the soil to the garbage dumpster.  If the plants were healthy, I will reuse the potting mix for three to four years.  Generally you need to add some replacement potting mix to the container before planting, so I do that and leave an extra one inch of space to topdress the container with a good, healthy dose of compost.  

When the potting soil seems to be worn out, as evidenced by the collapse of all the perlite or vermiculite balls or compaction of the peat and bark mix  which makes for slower drainage and poorer growth of your plants, I empty the pots into the vegetable garden and till it in with the rest of my organic matter, if the plants that grew in it last year were healthy.  Remember, though, if you had disease problems in your container plants, you'll want to destroy the potting mix to avoid perpetuating those diseases.

Wiese Acres concrete planters

There are some gardeners who tell you it is fine to use garden soil, at least in small amounts, in containers.  I have not had good luck with that, with one exception.  I have some very, very large containers that are built almost like raised beds, using landscape blocks.  Because of the sheer volume of soil in those planters, I have been able to use about 1/4 well ammended garden soil, mixed in with potting mix.  I mix fresh soilless mix into these planters each year to replace what's been lost in the previous year, and add about two inches of compost to the tops before planting.  I can add enough of both the potting mix and compost each year, that I don't have the issue of the mix "wearing out" and needing to be fully replaced.  Most containers don't hold enough volume for this method to work, though.

With what is spent on plants for containers, it only makes sense to invest in good quality potting mix that is made for use in containers.

Tomorrow we'll discuss some environmental factors to consider in successful container gardening.