The only foraging event I have cancelled (in ten years) was a seaweed workshop when a electrical storm was forecast. It would have been dangerous to be wandering around the low tide line with lightning striking. I do not cancel any events because of rain, wind or cold.
Plants and seaweeds are relatively predictable. The meteorological seasons do move about a bit compared to the calendar, but there’s never a seaweed famine or a year when wild garlic doesn’t grow. Fungi are a different story. The worst year I can remember was 2003, when the sun didn’t stop shining from March until October, and then there was an early cold snap. Very few fungi fruited at all that year. I do occasionally have to cancel/postpone fungi foraging events, because I cannot ethically expect people to pay me to take them fungi foraging if I expect to find almost nothing. I will give people as much warning as possible if this situation arises.
When is the best time to go foraging for fungi?
The main autumn fungi season starts some time in late summer after it has rained, and ends with the first big ground frost. The peak (in England) in any given year can occur at any time between the middle of August and the middle of November. On average that means the peak happens around the end of September and start of October, but it would be wrong to think that means if you go at that time, you are guaranteed lots of fungi or a wide variety of species. It doesn’t work like that.
This is England; the weather is deeply unpredictable. Sometimes it rains for the whole of August and in recent years we’ve had heatwaves in late October. The fungi usually do best when we have a mixture of these things – regular rain, but with some fine days inbetween, and with the temperature steadily dropping. They do worst when there has been no rain at all for several weeks, but even if it has been raining things can be sparse (eg if the slug population is booming).
For a few years I attempted to minimise the risk of cancellations/postponements by only scheduling fungi events in September and October, but I eventually came to the conclusion this was pointless, because the barren patches are just as likely to occur at the start of October as they are at any other time. It is simply not possible to avoid this problem: fungi foraging is a lottery by nature. Sometimes you go out and get very wet while you find nothing. Other times the weather is perfect and the fungi are super-abundant.