JMO and I'm sure it will vary from zone to zone but works best for me is early season extension for tomatoes rather than fall extension.

Fall gardening with covers and such works really well for many crops. Tomatoes isn't one of them for the reasons you describe - flavor - unless you are working with fresh plants.

Don't get me wrong those late fruit are still better than any you can buy in a store but they aren't the mid-season quality.

Instead I work to get my plants out under cover 3-4 weeks early for an earlier crop of good ones. Then mid-season they are replaced with fresh plants grown from cuttings for a better fall crop.

Dave

Dave, are there advantages for going from cuttings rather than seeds for the later crop?

I agree with Dave.
Best extension IMO is EARLY extension. Late season you get tired of tomatoes anyway. That is why, I am going to experiment with Low Tunnel and also I am building a COLD FRAME to shelter my tomatoes at cool nights untill it is goof proof safe to plant out.

ABOUT CUTTING VS SEEDS.
No doubt in my mind that cutting will be much faster and stronger but then WHERE ARE YOU GOING TO GET THE CUTTINGS FROM ??

Yeah cuttings save you a good 6 weeks over seeds, more if you time them right. Cuttings come from from your existing plants.

Dave

Cuttings come from from your existing plants.

Dave
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Yeah , Sure. I was talking about starting for the first time. If I already have the plants why would I want to start new plants ? Except if I want a late season crop down South or someplace.
I have done it in GA, both ways, from seeds and cutting.

Thanks for the feedback. Starting earlier wasn't something I had even thought about. This was a strange tomato year for me since the plants in open garden hardly grew and ended up diseased (cold, wet spring). The tomato plants I put in the high tunnel simply because I ran out of room outside thrived and were continuing to produce. Next spring I will attempt to get a couple of plants growing earlier.

EARLY EXTENSION starts with starting seeds inside 6 to 8 weeks before plant out time. Some of us do it under grow light and most of us buy plants grown by the growers in commercial greenhouses. Still the same idea; Bonnie or others do it for us.

But even then, a lot of times, a lot of places the nature is not friendly with us. So we have to fight back with new ideas to combat the elements. Low Tunnel, High Tunnel, W.O.W.... are the ways to do it.

Another way is to develop an plant varieties that can better cope in cooler weather in shorter time. If your season is short, it does not make sense to me, eg, to plant a tomato with 95 days DTM. Plant ones with DTM of 50 to 75 instead. So it is the battle of survival and adaptation that go hand in hand.

I use a few walls of water to get earlier tomatoes in my climate. Those don't work that well in cloudy dreary cold weather. They are a little bit of a pain but you don't have to use them on all your tomatoes. In July there are tomatoes everywhere. Those early ones are really appreciated.

If I already have the plants why would I want to start new plants ?

Why wouldn't you? Assuming you have the room to plant them there are lots of reasons folks do it. In addition to all the usual benefits of succession planting, you now have younger, healthier plants, and the size and amount of fruit produced are more like the mother plants produced early on in the season,

Dave

In answer to why start new plants I also wonder why folks just don't take better care of the plants they start early. I'm still picking from high tunnel plants I've picked from in mid-May. I hate to pull the plug (stop heating on cold nights) when many are producing new fruits in abundance. I'll grant that with many the flavor has not been as good as earlier but my feeling is that if one can raise the tunnel night temps consistantly to speed ripening of fruit the flavor will remain good.

With my setup the cost is only firewood and my loss of sleep to keep wood fired stoves emitting maximum heat. The feedback from customers raving over the flavor of my harvest has been my reward. I would like a higher packout percentage but the last tomatoes of the season, like the first, are like icing on the cake.

I also wonder why folks just don't take better care of the plants they start early.
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BECAUSE:
The two options (starting from seed early, indoor and providing protection for HUGE plants at the end of season) are not the same. I can easily manage to grow 20 tomato or pepper seedlings in my living room for 3 months. But I cannot accommodate even a single 6- 8 foot plant inside. The only option remaining is to have a greenhouse. Your high tunnel is just an attempt to create a greenhouse BUT a much less inefficient one.

That is why I BELIEVE trying to extend the season at the fron end is less costly and more convenient. ( for the reasons I mentioned above)

Seysonn, if huge plants are a problem for you then you must be content with the production limitations of smaller plants. I'll admit that I have "Maxed-out" on the tomahook stringline reserve on most cherry & grape varieties translating to plants that have grown well over 20 feet over the season and I agree that a greenhouse is the way to achieve more than season extension since the framework also serves as plant support.
I have grown tomatoes in the ground under high tunnels for more than 10 years now and I have made some changes early in the process that have made a large impact on success: Exhaust fans, circulation fans,a wood stove and lights. I could never understand why most people take multiple steps to improve their personal comfort yet draw an absolute line on where they cease to care for their plants. For the first and last months of the season the roll-up sides of my tunnels remain locked down and thermostatatically controlled exhaust fans keep inside temps in control. Circulation fans are a huge benefit in insuring uniform air temps, lowering fungal diseases and even in polination- they're cheap and pay for themselves many times over. As far as wood stoves go, it's just the cheapest heat source for most people when all factors are considered.

Starting plants mid-season means that for that ground surface area you have ZERO production from the time of transplant until harvest begins, usually 8-10 weeks. For me that translates to $thousands. Just do the math.