Last frost date confusion

This will be my first year growing plants from seeds - normally I just pick up the seedlings I need at various garden centers.

So, I headed over to Victory seeds, and looked up the last frost date for my area. I'm in Ontario, and literally right on the Michigan border. Naturally, I looked up Detroit first (5/12) followed by Port Huron (5/17) since they're roughly equal distance away as the crow flies. Then I noticed they have dates for Canada too - so I looked up Windsor (4/25).

Now, that's a bit confusing. I realize Windsor is actually further south than Detroit... but a two and a half week difference? Really? I mean, London, ON is listed as 5/9 - and as anyone from around here could tell you London has a much harsher winter than Detroit.

Which one do I believe? If it's the Windsor date... then I apparently should be starting my tomatoes next week lol.

Maybe call your nearest nursery or greenhouse and ask the manager?

Also, your local county extension agent is usually a great resource.

The logic of the hardiness zones is apparent from the map: water on two sides indicates warmer temps. Proximity to a smaller body of water on one side (Windsor) means the water there will heat up quicker, resulting in warmer temp. Also bear in mind that the hardiness zones in Canada may have changed like they did in the U.S.

Source: http://atlas.nrcan.gc.ca/site/english/maps/environment/forest/forestcanada/planthardi

Naturally, I looked up Detroit first (5/12) followed by Port Huron (5/17) since they're roughly equal distance away as the crow flies. Then I noticed they have dates for Canada too - so I looked up Windsor (4/25).

Now, that's a bit confusing. I realize Windsor is actually further south than Detroit... but a two and a half week difference? Really? I mean, London, ON is listed as 5/9 - and as anyone from around here could tell you London has a much harsher winter than Detroit.

Yes the average last frost dates can be confusing. Where I live, there are 2, 3 and 4 week differences for cites/towns on the same latitude, but within 80 miles, east to west.

Checking with a nearby nursery seems to be a great option.

Furbalsmom wrote:Yes the average last frost dates can be confusing. Where I live, there are 2, 3 and 4 week differences for cites/towns on the same latitude, but within 80 miles, east to west.

Windsor and Detroit are within a mile of each other, when I said that Windsor is further south that's really just being technical - the city core is slightly south of Detroit's even though the two cities are simply separated by the river.

Anyway - I checked a couple more websites and it seems to be just the way the data is being reported. The date in May is accurate when you want absolutely zero risk of frost; while the date in April is where the risk is acceptably low.

For instance the website listed in the sticky (which is apparently different than the one recommended in the book-whoops) says this when inputting the closest zip code:
- Each winter, on average, your risk of frost is from October 21 through April 26.
- You are almost guaranteed that you will not get frost from May 10 through October 4.

Ugh. I'm heading to the local garden centers this weekend to start getting materials for MM - guess I'll be asking for verification as well!

Thanks guys!

eflan, sorry I muddied the waters, but glad you found a sound explanation for the differences, due to the % of risk.

My last frost date is 118 days away. Do you know when yours is?

Mine is 90-95 days away.  It will be time to start some seeds indoors before too long.  I promise to not jump the gun this year, I promise not to jump the gun this year, I promise not to jump the gun this year.  Really...I promise.

30 days.   

My 50% frost date is 138 days away (June 5). However, my local nursery expert tells me that I can start many cool-season seeds as early as March--with cover. Thoughts, anyone?

87 days here

donnainzone10 wrote:My 50% frost date is 138 days away (June 5).  However, my local nursery expert tells me that I can start many cool-season seeds as early as March--with cover.  Thoughts, anyone?

In my area, some can be planted as soon as the soil can be worked, like peas & spinach.  Actually I planted spinach seeds last fall to see if they will sprout come spring.  But I prefer to start others indoors  - kale, collards, cabbage, lettuces and such.

LFD April 10th.  I think...  ...can't remember and don't want to get up to look at my 2014 calendar.

CC

Depends which website I go to.

Anywhere from 72 to 87 days.

117 days here. Thinking about starting my onion seeds indoors this weekend. It is about a month early, but if they don't work, it will still give me time to order some plants!

GG - itching to plant SOMETHING!!!

30 days or less, depends on which website or person who does the talking.
It was mid March last yr., but I was to sick to set out transplants. We had a hard frost the end of March! Mother Nature strikes again!
Jo