On Sunday, during a brief nano-second of sunshine, I ran into the yard to check on all my veggies. Everything in the slug biodomes seems to be thriving and I harvested a salad for dinner.

Some of the outdoor plants were definitely not happy; the zucchinis and beans, which I had left growing in the hopes of having one last fall harvest, were all mouldy. So much in fact, that when I pulled out the plants, clouds of dusty spores were released into the air around me.

Panicking, I pulled all the plants and the rotting veggies (boo!) into the garden waste before the mould could spread. Then, my rational left brain calmly took control, and reminded me of a few fun facts about mould  that I had tucked into my brain from my very brief stint as an indoor mould expert:

• Moulds are naturally occurring and widespread, especially in the outdoor environment. Outdoor air concentrations of mould spores and fragments depend on the season, climate, local vegetation and time of day, with levels ranging from < 100 – > 10⁵ spores/m³ [1].
• We are exposed to mould every day. There are over 100,000 different fungal species reported; humans are routinely exposed to about 200 types [2].
• Levels of outdoor mould are elevated by activities such as lawn mowing, gardening, leaf blowing, street sweeping, construction work.
• Moisture is the primary factor needed for mould growth. In addition to moisture, mould requires oxygen, a carbon-based nutrient source, and an acceptable temperature range.

Although numerous studies have concluded that the growth of visible mould indoors, regardless of the species or the amount, is inappropriate and needs to be removed, moulds are naturally occurring and widespread in the outdoor environment. Removing a few mouldly plants from my garden is unlikely to make much of a difference in overall mould levels. Removing a mouldy plant may not reduce the chances that the surrounding plants start moulding, as (in theory) those mould spores are already present in the environment. However, mouldy plants looks awful, so just from an aesthetic perspective, they are worth removing. So, garden activities in the next few weeks will focus on removing wet and mouldy plant materials and weeds….

Some references:

[1] World Health Organization. WHO guidelines for indoor air quality: dampness and mould. 2009.

[2] Institute of Medicine. Damp Indoor Spaces and Health. Washington, DC: National Academies Press, 2004.