Probably 2-3 weeks after your average last frost date is safe most years as long as you are prepared to cover them. An old bed sheet, frost blankets, 5 gallon buckets, and the card board boxes you mentioned can be used to cover them but if you have already staked or caged them then only the sheets or frost blankets would be options. You can also use the wall-o-waters to get a jump on planting out (link below). I usually shoot for 2 weeks after average LFD and have backup plants that I start 2 or 3 weeks later just in case, but I only plant about 8 tomatoes. I don't like my Tomatoes to be out in temps below 40d.

Wall-o-water

Wall-o-waters are a good strategy provided that:

A) you set them out for a few days in advance in order to ensure that the soil under them is nice and prewarmed for your tomatoes

B) you tomatoes are not so large that they are taller than the top of the WOWS, such that you can close the teepee at night.

C) you are able to remove the WOW soon enough that the plant is not too big that the removal process will break it, and soon enough that the root ball is not so big that adding a support will damage it, because you can't really fit the WOW around a tomato cage very well (I tried that one year, and ended up either removing/replanting the cages or puncturing the WOW trying to slide it up over the cage).

If those conditions are satisfied, I find they work better than sheets, frost blankets, cardboard boxes etc. because they don't blow away in the wind and you don't have to constantly remove/replace them daily. Just need to pull them open in the AM and close them at night. Also, if you time it right and keep an eye on the weather, you can drastically shorten the hardening off period as the plants will slowly harden off in the WOW.

LFD is a good bench mark not a rule set on the stone. What it means is that there is a 90% chance that there won't be a frost after that. In some place it warms up quickly , even starting days before LFD.

LONG 15 DAY FORECAST.

Weather technology at the tip of your fingers, use it. I look at the forecast about a week before my LFD and plan accordingly:

Case In Point:

Today is my LFD but I have been hardening off for the past 7 days. Today I will start planting out. B/c we have very nice warm weather for the next 15 days. It is Like May weather. So I take advantage of this an get a head start.

In South Carolina , ( wher your LFD is Feb 14) you could've started around that date or couple of weeks late, say early march. In Atlanta ( LFD =Apr 7) I have planted in late march.

On the other hand, you have a long season. Couple of weeks won't make a difference. But in my location, with cool summer and short tomato season, every day counts.

Sey

Thanks for the responses.

Sey, I don't have a long season. I have a long period of time that is frost free, but I have a very narrow window of time that is pollination friendly. Starting in mid June temps will exceed 90 degrees many days. Combine that with high humidity and tomato production stops. My plants must mature, flower, and pollinate before June 15. I planted out 15 March. I will have some success, based on what has happened in the past. Not even big beef will pollinate in July. The vines go into idle mode, most of the hybrids live, most of the OP die. I will check out the wow and the earliest plant dates.

That's an excellent point about the restricted time period that is "pollination friendly". Northern gardeners often don't quite understand that. My peak tomato season is May and June. After that, it's pot luck, and if you want to take the effort, it's mostly about keeping the plants alive until fall. Our summers are long, but our fruiting season is probably about the same as for those way up north. That's an excellent reason to get your plants big asap, and ideally planted out asap.

My strategy is just to plant within a week or two of LFD, and just be prepared to protect. Protection is hardest for my cherry tomatoes, which are planted under tall chicken wire trellises. Those trellises make it hard to cover the plants. I've thought about getting some thin plywood or paneling sheets that I could just lean against both sides of the trellises, but just coming up a foot or two on them. That would seal the plants up up pretty well.

Time Flies :

It was just like yesterday (April 5th) that I began planting out. That is ~ 47 days ago. We has a pretty good weather during April and early may. I measured some of my plants ; They are 38" tall. About 50% of them have flowers (maybe a few have set ) and another 40% have buds.

My goal is to have ripe tomatoes to celebrate The Fourth. I am betting on Big Beef and Better Boy.

sey

Sey, I'll bet they both will be tasty! As for setting plants out, we use the ground temperature in combination with the LFD. We've got lots of ways to keep them from freezing if the temps drop for a night or two, but if the soil isn't close to 60F our experience is that the plant will just hibernate (so to speak) rather than grow vigorously. So we use a high tunnel, row covers, and black plastic to heat up the soil to get an early start. I also consider that possibly global warming has affected the timing of frost dates, so I'm more likely to take a chance - this year we transplanted 2 weeks before the LFD.

There are the mentioned technologies and a combination of those and a few more homemade remedies that you could use to have plants producing earlier and to keep producing longer. Some of the same row covers that keep plants protected from frost might also be used to shade plants on hotter days. I wish there were a good season extension forum. The Greenhouse forum seems more devoted to elaborate house sunrooms. High tunnels and Low tunnels are inexpensive ways to gain at least a month of extended season.