I think the average last day for frost in much of MN is the 20th or 21st of May, so grandma might be right about that.

Here is a link you might find interesting.
http://climate.umn.edu/doc/agwx.htm

Used to be no one would put their tomatoes out until Memorial weekend. My grandma wouldn't plant anything much until around then (which is also around her birthday). My husband and I would go over there and do a massive planting for her birthday gift every year until just last year when she moved.

-Marie

I am prob. the over-zelous type gardener...I have been begging to put thingsout for a month now! But.......

Growing up (all of my 30 years!!) my mother and grandmother planted their tomatoes etc. on Mother's Day!! That was our Mother's Day event!!! So...I always remember that andeven though I may not listen to what they have instructed me to do.....that is the DAY they marked!

Granted.......climates have changed in 70+ (Heck...when is the last time we got 5 feet of snow???)years and my grandmother was in Pierz MN and I am in Hennipen county....that is how I justify putting things out early!So....based on this...um.....when I plant early I am RISKING losing everything, I know!
Bec

I planted tomatoes once, in Nebraska, on the 14th of MARCH! They made it too, and I Only had to cover them a couple of times. But that was a really strange year. Once the ground has warmed up to a reasonable level, I think how early you can plant is directly connected to how willing and able you ate to cover them up and take care of them if it gets cold. And of course, there's that odd year that it's going to get really cold for several days and it won't matter how well you covered them! Funny... I never thought of gardening as being like gambling until now :-)

I see all these people buying tomato and pepper plants in the 'box' stores, I wonder if they are covering them or keeping them inside before planting?

For me the fall is a lot more problematic..

I have a lot of plants that have to over-winter inside (it's absolutely insane, I know)...some I have to make sure to get in before the temperature drops too low at night(banana's, tacca's) and others (fig trees) I have to leave out til the first frost so they'll go dormant and then get wrapped up for their winter inside the garage -but before there is a really 'hard' freeze...I've had a couple of close calls because the weather is just as unpredictable then as it is in the spring.

If nothing else, gardening is challenging here in Minnesota!