I was hoping you could help me identify what a cluster of white work like substance that has appeared near the thyme shoots on my herb bed… Is it something I leave along? Get rid of immediately? It seems to have appeared quite suddenly.
Thank you for contacting Toronto Master Gardeners.
Although the picture is not clear enough to tell exactly what is happening on top of your soil I am going to assume by your description that the mass is not moving (i.e. they are not actual white worms) but it is static instead.
I suspect in that case it may be some sort of slime mold. Slime molds, although not really a fungus, are normally a temporary nuisance confined to small areas which seem to appear suddenly. Slime molds are often found on mulches, compost and old well-rotted logs, where they can find the moisture and bacteria required for survival. They can also clump together when looking for food appearing as a mass. They are harmless to plants and feed on decaying organic matter, fungi or as mentioned, on bacteria. It should eventually disappear on its own but you can remove it and place it in your compost pile. The best approach to controlling slime mold is by modifying the environment (reducing moisture for example).
What appears on top of your soil could also be a fungi. Soil fungus naturally occurs in the soil and are an essential part of healthy soil as they sequester carbon and break down organic matter so that nutrients become available for plants (However, not all fungi are good for your plants and some species can be pathogenic). There are millions of different fungi species. Potting soils, mulches and composts can be a source for several interesting fungi. If unsure, you can remove the fungi from your soil and dispose of it. The best way to deal with a fungus is to take preventative measures: control moisture, avoid waterlogged soil, increase airflow and sunlight, avoid compaction, feed the soil with nutrients to keep healthy plants and use reliably sourced potting soil when planting seedlings.
Hope this information is helpful. If we have not addressed your query, please feel free to contact us again.