Piling up billions of plastic containers in waste facilities is a dreadful thing, so I am hopeful that biodegradable pots will catch on.

In the meantime, many are trying to employ plastic containers in new, less wasteful, ways. Thus reusing containers is now on the rise, and I think this is sometimes having negative effects in terms of plant disease management via sanitation - our key control method.

In particular, I’m seeing more and more black root rot (caused by) in bedding plants, and I think this might be due to the trend to reuse containers. This is primarily a disease of pansies and violas, calibrachoas, petunias and vincas, so it would be a particularly good idea to use new, clean flats, packs and pots on these crops.

We see occasional Thielaviopsis outbreaks in bedding, flowering potted, herbaceous perennial and herb crops; verbena, snapdragon, leucanthemum, gaillardia, European ginger, rosemary and poinsettia are examples.

In an operation with otherwise excellent sanitation practices, reusing pots without first removing adhering organic debris and then surface sanitizing could allow Thielaviopsis to cause trouble year after year, as it produces long-lived spores that survive long dry periods.

There are many other, more theoretical, fears of pathogens surviving on flats, packs and pots from year to year, but I’m convinced that container reuse can make a Thielaviopsis problem into an annual problem. Using 1-gal. pots from a crop NOT prone to Thielaviopsis for herbaceous perennials would be a reasonable practice, but be forewarned that we are seeing more cases of Thielaviopsis in perennials in the past few years, so they should be protected from this pathogen just as carefully as you protect your pansies.

Incorporating a biological control into the medium of reused pots would be a great angle, but at this point I’m not aware of any biocontrol product with strong action against Thielaviopsis. Keeping the pH lower than 6.0 helps a lot; high pH favors the disease.

Power washing to remove organic debris followed by a treatment with disinfestant materials such as GreenShield or Zerotol would be an insurance step that you could take if the labor and time were available.

There are of course an assortment of other pathogens (besides Thielaviopsis) that could come back to haunt you if they were present in the first crop (e.g. Rhizoctonia, Pythium, Phytophthora, Fusarium) unless they were cleaned off the pots.

There will always be more risk in reusing pots than in starting with clean ones, but I believe that carefully managing that risk will make it a reasonable rather than a foolish practice.
Thielaviopsis basicola