Generally there is a significant time lag between 'average last frost date' and the suggested plant out date for hot season crops (like tomatoes and other solanaceae) because the soil is not yet sufficiently warm. Ideal soil temps for tomatoes to promote healthy growth is 60F for daytime temps and no lower than 55F for nighttime.

My last frost date is the end of March, however May 15th, or better yet, June 1, is the recommended date for setting out tomato starts because our soil warms up very slowly in spring.

You can plant out before that but cool/cold soils will stunt any growth and can actually set the plants back.

Thanks. I didn't realize that one could still pexperience frost after the last frost date!

Regarding soil temp- I imagine soil heats up faster in a raised bed? Daytime air temps will be in the 70s and 80s here for the next month.

The "last frost date" is (unless specified differently) shorthand for "MEAN last frost date". You can predict exactly when the spring equinox date is, or the date of Easter, but no one can predict what the actual last frost date will be.

Low soil temperatures won't kill summer vegetables. Just slow down their growth. Frost will kill them. So the plant-out decision is more the latter than the former. Once you're pretty sure your veggies won't get killed, it's up to you to decide how fast you want them to grow. For example, if your seedlings are getting too big, and the chance of frost outside is minimal, just plant them out. The time they would spend indoors getting root-bound, they would instead be slowly developing a real root system outside.

Soil temp in a raised bed is more closely coupled to air temperature than soil in the ground. In fact, in a raised bed, the soil temperature is likely to stay pretty close to the mean air temperature, especially if it has been cultivated.

My mean soil temperature pretty much never gets lower than 45F. At least the soil temp is no problem for tomatoes anytime.

With today's weather forecasting technology you can beat that Clemson University's recommendation. If you are a week away from your LFD and the 10-15 days forecast looks without a risk you can go ahead and plant out even few days ahead of your LFD.

We don't live in the Old Almanac era anymore.

sey

Laurens County here, also the Piedmont SC, and I used a different source apparently, Perhaps you are reading the date for mid state/ coast. Clemson usually gives the three regions. Depends on which extension office wrote the info sometimes. For me It says Last frost date of April 15-20.

Also here is a general link to soil temps which is what I do for seed planting. http://www.agweb.com/weather/soil-temperatures/

I'm thinking we should be safe after the cool off/storms this week, but mine are hardened off

Thanks everyone. This is all really helpful information. My plants aren't quite ready to go out, but I was curious about the discrepancy.

Cher- I'm in Laurens county too. I'd be curious to know your source for frost dates, as I checked several sites that gave the same date. I will have to double check!

I use USDA agriculture website as the base, but may have picked up a different date from another site. I know the Government usually only updates info every ten years so the reference might have been old too. That said I'll be planting the tomatoes this weekend. The peppers are lagging so I'll wait a week or ten days...the soil should warm considerably this week. Who likes cold feet? Wishing you a bountiful harvest!

I always plant tomatoes before the last frost date. Soil is warmed in advance with black plastic, but I think soil temperature is seriously overrated.

Each plant is surrounded by passive solar (Water Walls or 5 one-gallon bottles of water), with a fitted sewn floating row cover in a pvc frame over them. On cold nights, a bed quilt covers them as well. I have been worried sometimes when a frost gets down into the twenties. But I have never lost a planted tomato to cold.

It takes me a while to plant and cover everything, so that some may be planted almost two weeks later than others of the same cultivar. It is ALWAYS true that I get more produce from the ones planted earliest. I think I found waterwalls about 40 years ago. In all these years as a tomatoholic, I have found the ideal time to plant is TWO WEEKS BEFORE LAST FROST DATE. Those are always the healthiest plants all year.

Go ahead and get your tomatoes in the ground now, but be prepared to possibly cover them some nights.

I find the row cover and waterwalls to be a tremendous benefit to tomatoes in general: bugs, humidity, etc. They love it. I keep it on until the plants are too big.

Our LFD is April 10, 12 ?

I planted out 3 weeks early. By LFD I had couple of golf ball size tomatoes (on one variety )and now 50% of my plants are over 18" tall with flowers and some with small fruits.

Previously ( on March 7 ) I planted out about 12 and the we had a surprise freeze (not just frost !) The lows dipped to 24F, with high winds on March 16 and 17. Even though i did my best to protect my plants , ended up losing 7 of them.

But that was not a big deal . I had over 40 more plants.

Just 5 days ago we had a frost with low @ 35F. But it did not do any damage to tomatoes and peppers.

So you have to decide where your comfort zone is. Can you take calculated risk ? My corns are up but no farmers around here have planted corn yet. There is an older man with a big garden plot down the road. He has just plowed his garden.

A lot of people still go by the book and outdated Farmers' Almanac, phase of the moon and that sort of things.

After all, you are the king and you rule in your garden. .

sey

Sey:

I noticed some of the gardeners in my area, which gets too hot too soon ( my zone is more 9a than 8 b) situate their garden so that shade hits it in the late afternoon. That might explain your nearby gardener neighbor plowing so late. Maybe his garden gets late afternoon shade in July/August. Shade is a kind of season extender, protects against heat to extend the life of the plant, and may even allow some pollination.

Tomato planting time for you on your site is when your days, nights and soil are warm enough for them. If you want to speed things up use shelters to provide a warmer environment than the open garden. In my cool summer area there are hobbyists who grow tomato plants under cover the entire season.

"A lot of people still go by the book and outdated Farmers' Almanac, phase of the moon and that sort of things."

I wouldn't dismiss that as some sort of mystical foo-foo nonsense!! There is a great deal of reality and common sense behind many of these practices, which have been established by hands-on gardeners and farmers over many generations. I would tend to put a lot more faith in these so-called "outdated" guides and practices than some hotshot online presence who may or may not have the gardening successes they claim by defying the odds.............your choice :-))

Phase of moon is foo-foo. Let's leave it at that. There is a great deal of mythology that has been created by "hands on gardeners" that doesn't correspond to any semblance of scientific reality. There is also a great deal of practical knowledge that has been created by them. The trick is to distinguish between them.

"Phase of moon is foo-foo. Let's leave it at that. "

LOL!! Only if you claim it to be. The moon has a very strong effect on all manner of phenomenon, not the least of which is plant growth. And this HAS been established scientifically.

The validity behind moon phase planting and plant growth.

Ha ha. By "Marion Owen, Feerless Weeder for PlanTea Inc." Give me a break.

"In fact, my
friend Amy braces herself before going to work. Amy works at
the hospital and when the moon is full, those nights in the emergency
room are, as she calls it, 'memorable.'

Many scientists insist that the myth that a full moon affects the behavior
of humans, animals and plants is a bunch of baloney. But police, bartenders
and folks like Amy will tell you otherwise."

That's her "science". Take it from police, bartenders, and Amy, whose plant biology is unsurpassed! Hey, let's get some bartenders in here to give us some great scientific advice about gardening.

C'mon GardenGal, take a deep breath, and forward me Marion's horticultural credentials. Maybe a scientifically refereed paper or two? If you want to use the words "established scientifically", please use them correctly. On the other hand, if you just want to say that Marion makes up keen myths out of whole cloth, I'll accept that.

Sure, moos has effects on Earth, governed by the general law of gravity , discovered by Newton. . Low Tide and High Tide I know about. But it has nothing to do with the phase of moon but rather where and when it is/isn't up there.

It may have some effect on the plants too but I think it is insignificant. We know that moon is not a source of light and energy. It just reflects a minute amount from the solar light. JMO

Precisely. The Moon has enormous effects on terrestrial biology, mainly through the tidal cycles. But the tidal cycles have little to do with the lunar phases. Actually, they have an itsy bitsy bit to do with lunar phases, as tides at new Moon and full Moon are incrementally different than tides at quarter Moon, e.g. "spring tides".

More on the Moon and plants later.

C'mon guys - let's open up our minds a bit and be a little bit more receptive to natural phenomena that may not have well documented evidence! I did not mean to imply that the link I referred to WAS the scientific evidence but there is little disputing that the lunar gravitation pull that results in tides (which ARE related to the phases of the moon) also have an influence on other fluids, including those in our own bodies as well as those in plants. Try expanding your knowledge base with readings like 'Moon Rhythms in Nature: How Lunar Cycles Affect Living Organisms', by Klaus-Peter Andres.

Although this is an interesting topic and worthy of discussion, it has very little to do with when it is appropriate to plant out cold sensitive plants. That is really ONLY determined by daytime and nighttime air temperatures and by suitable soil temperatures. The approximate dates when these occur tends to be very cyclical and documented by area and THAT is what the Farmer's Almanac is attempting to relate. Nothing outdated or mystical about that.

Hmmm. Natural phenomena that may not have well documented evidence. That's a good one. You mean made-up stuff that people haven't been able to establish any real truth for?

But yes, this discussion is inappropriate here.

More on the Moon and plants here -- http://forums2.gardenweb.com/discussions/4584623/m=23/the-moon-and-plants .