Success is in the soil

Potting soil. Every garden center sells it, but do you really know which potting soil is best for specific uses? What if a customer wants to plant an indoor hanging basket? Save an ailing peace lily? Plant kitchen herbs on a windowsill? Can your staff answer each of these queries about houseplants with authority? If not, perhaps it's time to read a few product labels at the next employee meeting.
 

Not just dirt. What's the scoop on potting soil? Is it soil? Is it container media? While it goes by many different names, in general, potting soil = container media = potting mix = container soil = soilless media.

None of these have any actual soil (sand, silt and clay) in them. Regardless of what you call it, houseplants need a special type of potting soil, different from potting soils used for outdoor container gardening.

Should it be organic? This depends on your personal outlook. I choose organic potting soil because it makes the world more sustainable. Organic is a lifestyle choice. Consumer research shows this rising tide of shifting paradigms towards organics continues to affect consumer buying habits.

Houseplants thrive when repotted annually, to refresh porosity within the growing medium and remove any excess salts present from over-fertilizing. Potting mixes that contain high percentages of easily degradable organic materials lose the majority of their pore space within one year. Pore space is extremely important when container gardening. The water-holding capacity and air space present in a potting soil is only as good as the total pore space. These are all good talking points when educating a gardener about repotting.

Yet, every potting soil blend on the market has easily degradable ingredients like peat moss or coconut fiber. Thank goodness there are other ingredients as well. Aged barks are very common in most potting soils. The East Coast uses pine bark, and the West Coast uses fir bark.

Perlite, vermiculite or sand is added to indoor potting soils to provide a mineral element and increase drainage. These three ingredients do not break down, thereby conveying their benefits for the life of the potting soil. Vermiculite has the added benefit of nutrient retention, imparting its ability to hold onto fertilizer. Sand and perlite are strictly for drainage and creating pore space.

Compost and worm castings are also organic ingredients for potential inclusion into potting soils. Compost can successfully be used to reduce or replace other common ingredients in container media.

Compost destined for potting soil must be a higher grade than compost destined for lawn areas or raised beds. How do you tell if the compost is high-quality? You talk to your supplier about how the compost was made, how it was tested, and their compost specifications.
 

Blends matter. Now that we've covered ingredients, let's talk blends. When shopping for a line of potting soils, look to see that the company sells one soil especially for indoor houseplants. Houseplants require mixes that hold moisture longer than outdoor container blends, since outdoor potting soils need exceptional drainage to deal with excessive rainfall. If a customer repots a houseplant with a container media designed for outdoor use, it may dry out faster than it should, resulting in wilted appearance or yellowing leaves, especially in the winter months.

There are a few things to watch out for when receiving your next shipment of potting soil. Make sure to inspect product upon delivery; not the day after, or the week after. If fungus gnats are noticeable, bring it up with your supplier immediately! Even sterilized potting soils can have fungus gnat infestations. Ever smell alcohol after opening up a pallet of soil or mulch? Potting soil that smells like alcohol when opened should not be used, as it likely contains anaerobic materials.

What is the No. 1 customer complaint about houseplant potting soils? "I repotted my plant, and now it has mushrooms growing out of the container." The easiest way to avoid carryover by certain fungi is to remove as much of the existing potting soil from the root ball as possible before repotting. Take it one more step by gently washing roots of clinging soil particles to remove them. If the customer is not up to this challenge, another method to minimize mushroom formation is to keep houseplant potting soil at a consistent moisture level. Only when potting soils dry out frequently will fungi be able to grow and get a foothold inside houseplant containers. Make sure houseplant potting soil contains worm castings or similar to hold moisture in-between waterings to minimize mushroom growth.
 

What about fertilizer? Houseplants need less fertilizer than their outdoor counterparts, since light levels are lower inside. If the potting soil does not contain fertilizer, this is an opportunity for cross-merchandising. Consider recommending a small package of organic, slow-release fertilizer.

During the colder months, houseplants will use less fertilizer. This is important information for a beginning gardener, since over-fertilization during winter can result in leaf necrosis and tip die-back.

So are there different soil mixes for each type of houseplant? Not necessarily. Does sound horticulture knowledge come into play when recommending or selecting a potting soil? Yes. Plants that require drier soil conditions should be potted with a well-drained container media. For most houseplants that simply need moisture-retentive mixes, find one potting soil brand designed for use indoors and stick with it. Choose a brand that will resonate with your customers and staff. After all, if your staff doesn't LOVE it, they won't SELL it!

Mark Highland focused his studies in the Longwood Graduate Program on compost and potting soil. After completing the program, he started The Organic Mechanic Soil Co., www.organicmechanicsoil.com.