I have been in a discussion with others on how best to calculate the average date of the last frost of spring and the first of autumn

does anyone do this and if so how?

The others wanted to have an excel spread sheet to do it but I prefer pen+paper and came up with this:

is that in each year a number is allocated to the date of the last frost ie: 1st Jan' would be 1, 2nd Jan would be 2, 1st Feb would be 32 and as per the example below we get a mean number

1.) 1st June = 152 (that is the 152nd day of the year)

2.) 4th April = 94 (the 94th day of the year)

3.) 3rd May = 123 (the 123rd day of the year)

now add together 152+94+123 = 369

now divide 369 by 3 (No. of years) = 123

so we can say after those 3 years the date of the last frost in the spring was on average the 3rd May.

any suggestions welcome