Alys

FWIW, the zone business is in flux right now due to climate change. It's possible that some sites have earlier data than others.

I use the Arbor Day Zone map, linked below.

But if you're in an area that has various climate pockets, you might get more reliable frost date information by calling your county Extension Agent.

Here is a link that might be useful: Arbor Day Zones by zip code

Check with local gardeners or farmers. Find out when they plant. Ask at a good local nursery but ask enough questions so you can tell if the person really knows what they are talking about. Don't base your planting out times on when the plants become available as transplants at local stores. Around us, transplants arrive way too early and also way too late for conditions. If I planted tomatoes when they are in the garden centers I'd lose them all. The extension offices are also great sources for local info.

Since I'm a zone south of you in northern Arkansas and my last frost date is accurately April 15-20th I don't think yours would be earlier, more likely 2 weeks later ;) so it sounds as if your extension office perhaps gave you the wrong info.

But it all depends on the crop too. Lettuce and cole crops, peas, and potatoes are all frost tolerant and can go in much earlier than many other things so lettuce by St. Patricks Day may not be out of line at all. We plant our peas and lettuces March 1st and potatoes went in last week. May 1st is the recommended planting time for tomatoes and warm season crops here but we push the envelope and plant some things April 20-25th and then plan to cover it all several times. And yes, we often have to do just that.

So if you have ready protection available you could try planting earlier but otherwise, play it safe and figure May 10th. Local gardeners should be able to give you specific dates.

And of course, as Anney said above, all the zone maps are changing due to the weather shifting patterns so don't take any of them as gospel.

Dave

Alys

Apologies. Until I read Dave's post, I missed that you'd been in touch with your country Extension Office.

Apparently Missouri is one of those states that does not have one or two clearly-defined zones but several. I suppose the best you can do is find some nearby long-time farmers and pick their brains about frost dates.

A simple plastic tunnel or portable cold frame will extend your season. Warm up the ground where you will be placing the trasplants by covering it with plastic sheeting right now: the solar heat will concentrate in the soil beneath and warm it up so that the transplants have a new warm home when you are ready to plant them out.

You can easily prepare a portable plastic tunnel or portable cold frame (see picture at attached reference) which you place over the seedlings when you set them out. Keep the plastic tunnel or cold frame in place until a week or two past your last frost. This gives you a head start on the growing season--a longer growing season. And you can use the tunnel to extend the season by 2 to 4 weeks or more at the end of summer or in the fall.

Here's a link to cut and paste:
http://www.harvestwizard.com/2008/10/cold_frames_for_autumn_and_win.html

Here is a link that might be useful: HarvestToTable.com

I have seen some erroneous USDA zone information published by certain seed companies.

In a nutshell... The USDA determines zones on a specific percentile of frost probability derived from climate data.

The climate data is broken down into brackets like 50%, 70%, 90% probability of frost during a particular calendar date. The errors occur when someone chooses a more conservative probability than the one chosen by the USDA.

Take my zone 3B, for example. There is a possibility of frost at any time throughout the summer. This probability exists only in the 96th to 100th percentile of gathered climate data. So, if you were to use a 100% frost-free probability data set to determine zones, then much of the northern United States and most of Canada would be dead zones that have zero growing season. Well, we all know this is not true! We do have very useful growing seasons, despite the very rare July/August frosts.

Another misconception...
Climate data is determined by statistical records of temperature readings at about waist height. The temperature can be 6-7F degrees lower at actual ground level. They base the readings 3-4 feet off the ground, as it is assumed that a person will be outdoors walking, standing or sitting and will feel the brunt of the temperature at waist to chest height. It is also MHO that some misguided folks try to compensate for this 6-7 degree discrepancy, when in fact, the USDA already has factored it into their zone determinations.

PS: The same reasoning is exercised by builders when they install your household thermostat at chest height. It is assumed you will spend the majority of your time standing, walking, and sitting, rather than lying on the floor.

It's certainly weird. The USDA shows me in zone 6a, I think...I'm the little circle in the middle of Missouri. http://mgonline.com/zm_mo.jpg

The last frost date given on the county extension info is definately in April...for ALL of Missouri...http://agebb.missouri.edu/weather/frost.htm and it's 1971-2000 info, so I'd think we'd be warmer now, not colder.

The Old Famer's Almanac info shows my town as April 13. http://www.almanac.com/garden/frostus.php

Then USAgardener.com shows the same town May 22! http://usagardener.com/breaking_ground/frost_dates_usa.php

And of course, the seed companies are saying I'm zone 6, but giving me a May frost date too.

Guess I'll be getting some PVC and plastic and moving my husband's shop light to my sewing room where my starts are so they don't get too leggy reaching for the window in case I can't get things in the garden.

Actually, I may be the same zone as you, since I seem to fall in that little microclimate area. Would that be because we're on the river, I wonder?

I live closer to Springfield, MO and I have had a lot of success using the MU Extension guide for planting dates:

http://extension.missouri.edu/explorepdf/agguides/hort/g06201.pdf

Some years it works out great and some years, like last year, we had a surprise freeze on April 28th which had me scrambling to cover some things up. I've always considered our last frost date to be April 15th, but that's usually just an average. Good luck!

I have the guide printed out. I assume it uses the same info as the other MO info I showed, with April frost dates, since it has me planting peppers by May 10, and you sure wouldn't plant them before the last frost date.

That hard freeze last April was fun, wasn't it? Saved my veggies, but my flowers bit the dust....A girl has to have priorities.

Intellicast.com is a weather site that can be localized. On your local home page about 1/2 way down click on 'historical weather data'. You get monthly daily and monthly yearly weather info. Cool place. You have to remember the USDA data is based upon a 30 year moving average low temperature.

The hard freeze last April was crazy! Let's hope that doesn't happen again this year. I've used that guide for several years and still look at it every spring for a refresher. I also watch the extended weather forecast and I'm usually able to sneak some things in the ground before specified planting dates.

I'm sure a lot of mainstream plant and seed retailers would love to make gardening as fool proof as possible. Fudging the last frost date, while good for the peppers, tomatoes and eggplant, is not so good for the onions, radishes, and spinach.

Get your frost date from the USDA (the source), watch the forecast closely, and make an informed decision about your planting dates.

FWIW, I can sometimes get away with planting tomatoes, peppers and eggplant in zone 3B on May 15th. Today it is -5F degrees below zero, and at night it will be -10F to -15F! Surely, the cold up here rarely makes its way down there in April.

Continental climate zones have radical swings in temperature, any time of the year, and Missouri is not exempt. However, on May 15th there is probably a 70% chance of frost up here by Canada, while the probability is closer to 10% in MO.

Some good info. USDA hardiness zones refer ONLY to a long-term average of the annual minimum winter temperature. That's all. It's good to know your zone to determine which perennials are likely to overwinter and grow another year. In the eastern US, it's possible to correlate these zones with some sort of expected first or last frost date. In the western US, not really. Northern FL, southern TX, and parts of the coastal NW US may be in the same hardiness zone, but the growing season lengths are different. Here in Zone 7b SC, our last freeze can be anywhere from late Feb to mid-April. And it's very different year to year. I always stagger my sowing times, both indoors and out to account for this uncertainty.

Here's some NOAA info that illustrates the wide swing in calendar date, between the a 90% frost probability to a 10% frost probability.

Select your state for detailed info and download the PDF file. (Adobe Acrobat Reader needed to open the files.)

Here is a link that might be useful: station freeze/frost probability tables for each state

That was pretty interesting. Thanks for the link!

I think alot of times we get caught up with "hardiness zones". Your right Dave, it's only one piece of the puzzle. It's best used for overwintering perennials and not annual veggies. There can be a 5+ degree difference in night temperature between the top and bottom of a hill. So microclimates play a huge part and I wish more would understand this. I agree, staggering seeding times is your best bet. Don;t put all your eggs in one basket!

I remember reading somewhere that you should watch your lilacs and plant cool weather plants like peas and onions when the leaves are the size of a mouse's ear. Then when they are in full leaf, and the maples are fully leafed out, plant things like tomatoes. I previously lived in zone 6. Going by the calendar there, we would plant peas and onions on St. Patrick's day, lettuce and herbs April 15, and tomatoes and most frost sensitive plants on May 15.

I think you have the right idea jaymo49. Just going by the calendar date to plan things like planting seed or transplants isn't good. It's best to use that as a rough estimate, and then tweak it by carefully observing other 'indicator' plants around you. Of course, I like my idea of staggering planting dates too, so you'll be ready for anything. And it spreads out the harvest. How many people plant all their cucs, or squash all at once and then have way too much to harvest for a few weeks, and then nothing.

Well, you can do that, or you can easily plot your plantings based upon readily available data that has been conveniently gathered for you by seriously hard workers over the course of several decades.

There is no mystery to the frost thing. Look at the data. Study it. Enjoy it. It is what it is.

As was said, the USDA Hardiness Zones indicate the average WINTER minimum temperatures.

Most of us do not garden where we can grow peppers, for instance, as a perennial. We grow them and most of our vegetables as annuals. The hardiness zones can only really apply to things like asparagus, cardoon, chives, Jerusalem artichokes, rhubarb, and walking onions. (And, that is of really a "so what" importance.)

The "station freeze/frost probability tables for each state" linked above is the source of useful information on frost dates for our vegetable gardens.

dave_f1 says: Northern FL, southern TX, and parts of the coastal NW US may be in the same hardiness zone, but the growing season lengths are different.

Spring Dates:
50% Probability Level of 32°F
All Zone 8:

 Gainesville, Florida February 12
 Austin, Texas February 17
 Aberdeen, Washington April 01 (5 or 6 weeks later)

Steve

I find that even though we're now considered zone 6 in the Poconos, we are also at higher altitude (1700' up on my mountain.) So I plant as if it were zone 5. I also ask the old timers for their schedules, as well as the guys at our local Agway. And I buy seeds, plants from sources in MA, VT, ME, so I know they're tough enough to handle our weather here.

Zones? Doesn't matter. Who really cares what zone?

You still have to determine when the last date of frost will occur in our temperate latitudes, if you want to plant vegetables.

That's all I'm gettin' at. If you want to go through the bother of crunching the data, then go for it, but I already gave you the data collected by NOAA. You already paid them to collect the data so why are you all so resistant to using it?

Just go to the link and download the appropriate file for your state.

Are you guys upset that you cannot divine frost with twigs or bent wires?

"You already paid them to collect the data so why are you all so resistant to using it?" Probably because for some of us, that info is almost useless. The information at the link you gave above is excellent, as is the advice to check historical records collected by the weather experts, but for those of us who live where there hasn't been any data collected, it's really not that useful unless we want to guess a bit.

"Just go to the link and download the appropriate file for your state."
Did that. I'm in Spicewood, TX, and the nearest listed city at the link you gave is 25 miles away to the southwest. The info there varies wildly from another city 40 miles to the west of me and another big city 45 miles to the east ~ the variance is up to a month difference. So when should I plant? I think I'll listen to the old timers near me who know better than NOAA when to plant in Spicewood. And/or take Dave_Fl's helpful advice to stagger my plantings so I'll be ready for anything. No twigs or bent wires involved.