I used to live in Z6b, and May 15 was always the benchmark date for warm weather plantings. Veggies that prefer their air a bit cooler will benefit from an early-mid April planting.

What specifically are you planting?

Wow, there must not be much of a difference between zone 5B and 6 then.

May 11th is said as the date where there is a 10% chance of frost after this date.

April 27th is noted as the average last frost date - with a 50% chance of frost before or after that date.

Therefore, I base my 'last frost date' on May 11th to be safer than just 'average'.

Here is a link that might be useful: BsnTech Gardening Blog

Does it matter where you are in zone 6? Because by me (Boston), it's still just too cold in May to plant much (beyond the things that like the cold). I don't plant any warm-loving vegetables around here until mid-June. I know that I can do it earlier, technically, but I've never seen an advantage. They don't grow much and it just seems like extra time for the pests to find them.

Susan, I live out near Worcester, and mid to late May seems to be ok for me. Last year, I planted an expiremental cucumber on April 16, and it took off like gangbusters. I primarily garden in SWCs, and am able to cheat Mother Nature a little by having the soil warmed up more quickly

I am not sure if I understood the question or not, but I would go with my frost date + a week and then the 10 day forecast looking good, for summer stuff, as I left it later last year and it wasn't needed and this year I know I can protect them if necessary (hopefully!) but spring stuff can go out before, I made the mistake if thinking the start date and transplant date where one and the same thing, this year I have started a few cabbages, broccoli, cauliflower, and will add a few each couple of weeks, until the transplant time which seems to be 6 weeks before the last frost date, I may try a direct sow of these at that time to see what happens.
my last frost date is April 26th, and I am going to plant the end of the 3rd week in March, for such things?

We have May 16th here as well. Since I will be starting a lot more from seed this year, I will be able to experiment. If I do not shell out the money for "walls-of-water", I will shelter them with large juice bottles filled with water near them. what do you use, for putting out early starts?

West, what kind of vegetables are you doing? Peas and tomatoes are very different!

In my area of NJ, our average last frost is between March 30 and April 30. I plant my tomatoes in late April, as long as the 10-day forecast looks safe... accepting that if there's a late cold snap, I'll be running outside to cover them up with lightweight row cover/sheets/milk jugs/etc. I direct-seed beans and corn at the same time, but wait a couple more weeks to set out peppers, eggplant, and squash, which all really love the heat.

On the other hand, peas and spinach can be direct-seeded around St. Patty's Day. Lettuce and broccoli, somewhere in between the peas and the tomatoes =)

To chime in real quick here, it seems that the weather this winter has been colder than average.

Our weather man said our hight daytime temperatures for now should be around 38 degrees - and we are down around 31 - 32 degrees.

While it isn't a scientific estimate, it may be that this year's last frost date will be later than average.

I also noticed that Atlanta was only about 44 degrees yesterday - that seems pretty cool. Their normal temps are 57 degrees for this time of year.

Here is a link that might be useful: BsnTech Gardening Blog

Maybe this is too obvious, but if you look on the seed packets, they tell you when to plant things based around your last frost date: my broccoli says to put the transplants out 4 weeks before last frost, my tomato seeds say to sow indoors 6 weeks before last frost and set out when soil temps are 65 and above...

So, read each packet and use that May 15 date to figure out when you should be planting what where! :)

Cheers!

Sunni

I am using a combination of things, garden fabric, plastic low hoop houses, and WOW! I got 12 for a $1 each last summer, in a clearance section, so I thought it was worth a go, I can't see how they work in the fall?, but easy enough to use after my dummy run. last year I just used the 3 qrt apple juice bottles with the bottom cut off, as mini greenhouses, and will also do the same this year, as by the time they where too big for them, danger of frost, was gone, I think using a combination of factors for different types plants works for me.

Your planting times are based on your last frost date, not your zone. Others in your zone may have earlier or later last frosts. The zones are determined by low winter temperatures...that is important in determining perennial hardiness but doesn't mean much to most seasonal veggie crops. Within a zone frost dates can vary alot.

These veggies can go in very early....soon after the soil is no longer frozen and is able to be worked:
Beets, Carrot, Endive, Kale Kohhrabi, Leek, Lettuce, Onion Parsley Pea, Radish, Spinach, Turnip

A bit later as the soil warms some but frosts still occur you can plant more of the above plus these:
Cauliflower, Chard, Broccoli Brussel Sprout, Cabbage (transplants of all of these are good to use but if your summer doesn't arrive too quickly you could try direct seeding quickly maturing varieties)

At the time of the last frost you can repeat any of the above and also plant corn and beans.

Afer the soil has warmed more, maybe a week or two after the last average frost date you can put in the heat lovers....either seed or transplant:

Cantaloupe, more corn and beans...they might not have liked the cooler soil before, cucumber, eggplant, pepper, pumpkin, squash, tomato, and watermelon.

You can check the average last frost date at the site below. Use the 32 degree column.

Here is a link that might be useful: National Climatic Data Center

You can even plant couple of weeks before your last statistical frost date, if the weather is nice,If you can protect them , if you are willing to risk.
Certain flowers and vegetable do fine in cool spring days but cannot tolerate frost, like potato, tomato.
Then there are vegetables that even without frost can be stunned or they will just sit there and do nothing. I think cucumber family,basils, peppers and eggplants are good examples.
So with this group you are better off to wait even after the last frost date.

Here is another useful website for basic planting information with frost dates for many cities and lists of plants.

Here is a link that might be useful: Avg Frost Dates and Planting Guide

ok, I'm growing:

beans, corn, cucumbers, water melon, onions, bell peppers, zucchini, cabbage, carrots, eggplant, garlic, okra, hot peppers, potatoes, tomatoes, water melon.

actually i'm glad i did that, i hadn't planned that out =)

but i guess the ones i'm concerned about planting timing are the ones you CAN set out before may15 and which ones should be started early. particularly concerned about onions, cabbage, carrots garlic, potatoes, tomatoes.

the rest of them can be sown/planted on may 15 right?

One small additional point is that, while heat lovers such as tomatoes and eggplants can be set out soon after the frost free date, it often is not advantageous to rush doing so. The plants may be safe from frost, but will put on very little growth until the weather really warms up.

Jim

There is another factor to consider in addition to temperature - wind. The temperature doesn't have to dip below 32 degrees for the leaves of plants to be damaged. The wind dessicates and burns the leaves when the temp is near freezing. If you aren't going to protect seedlings from wind then it is a good idea to wait an extra 10 - 14 days.

This advice even applies to brassicas. I find that a few weeks of wind protection does wonders for these seedlings.

Soil temperature.

Last frost dates are a fair GENERAL guideline across a zone but soil temperatures in your own garden are the best and most accurate guide to use for "when to plant". Every plant has a minimum, optimum, and maximum soil temperature planting time and charts are readily available for them. Linked one below but they are available from many different sources including county extension offices.

So learn to monitor your soil temperatures at root depth - it is easy and inexpensive to do - and don't focus so much on air temps - they change from hour to hour while soil temperatures are very very slow to change.

Dave

Here is a link that might be useful: Soil Temp Planting Guide