You can always prune them. My cherries (they are vines, really) get to 14 feet long every year, and I just let them drape over my trellises. I don't think there is such a thing as "too long", unless the vines are draping over onto the ground, or it is so hot the vines have trouble pumping water that far. I suppose if your trellis doesn't have strong lines, that could be an issue as well. Next year, use wire or stronger string.

BTW, epsom salt is often spun as a magical fertilizer. It isn't, unless your soil is deficient in magnesium. Most soils are not. You might have your soil tested to see where you stand. Sandy, acidic soils that get easily leached are sometimes Mg deficient.

Are you pruning to one stem? It doesn't look as if they have very much room there, so that's what I'm guessing and that one stem then goes nuts. I tend to let mine just grow however they like and they don't usually get much above my 6' trellis.

Thanks.

I'm know well that Epsom Salt isn't a great fertilizer, but if you're deficient in magnesium it works wonders. From everything I've read, most soils don't have enough magnesium for tomatoes which are heavy users. I guess it's possible, though unlikely, that I'm deficient in sulfur. Either way, it worked wonders. My yield tripled from past years.

Well, the standard advice is not to apply a magnesium supplement unless symptoms of magnesium deficiency are apparent - mainly interveinal chlorosis.

https://extension.sdstate.edu/monitoring-and-correcting-magnesium-deficiency-high-tunnels

https://extension.umn.edu/manage-soil-nutrients/coffee-grounds-eggshells-epsom-salts

Not to say that this wasn't your problem, but there are many factors that can change yields from year to year. A soil test would be smart.

If you don't like indeterminate varieties why not to grow determinate Adam? They would fit better in your growing boxes.

Just FYI, regions of the U.S that have most serious Mg deficient soils are in the deep southeast. The western U.S. is largely Mg rich. A detailed map of Mg content is shown here.

https://pubs.usgs.gov/sir/2017/5118/sir20175118_element.php?el=12

Now, one has to be a little careful in that Mg is not necessarily in plant-usable form.

With regard to plant physiology, this is a less detailed but perhaps more accurate reference map.

https://www.thioguard.com/newsletters/2019/html/newsletter-04-22-19.html

These maps are largely, but not entirely, consistent.

My own (alkaline) soil tests out as 0.15% Mg, which might be classified as mildly deficient, but the soil analysis report from my extension called it "high", and recommended no Mg fertilization.

windberry, I didn't say I don't like indeterminate varieties - I love them. I only asked what folks do when they get too high to support. I can support them to 7' but after that they lean over and crack.

daninthedirt, I definitely had symptoms of magnesium deficiency. Over the last several years I've had VERY poor yields, yellowing lower leaves, etc. I bought Raised Bed soil in bags from Home Depot so what area of the country I'm in had little to do with the soil composition. The only thing I did differently this year was fertilize a touch more and use the Epsom Salts.

It may be anecdotal, but the difference was stark.

Thanks all!

That's a valid point that bagged soil has goodness knows what nutritional deficiencies. But to the extent you had symptoms of Mg deficiency, Epsom Salt was a reasonable strategy. You'd like to believe they'd do some basic testing to see what is lacking, but who knows?

Here's an amusing page, where they tested various commercial soils. Almost an order of magnitude difference in Mg among them, and those on the low end (with ~80 ppm) are certainly borderline deficient. Wildly different amounts of other important nutrients. This might be considered a warning to those buying bagged soil for their beds. It might look good, and feel good, but ... That is, just because it comes in a bag doesn't mean it's really that good. Of course, in principle, you can say the same about any random mix.

https://extension.uga.edu/content/dam/extension-county-offices/henry-county/anr/AG%20Poster.pdf

As far as trimming plants the deer trim off whatever grows out thru the fence and it doesn't seem to be detrimental to production.I've grown tomatoes 14 feet high and production seemed normal. This year tho I made a new hot frame and some of the extra beefsteak seedlings were left to grow out. Those seedlings apparently rooted deep enough to find the foot of horse manure down a foot. Those plants are enormous and have only a few tomatoes on them. The beefsteaks I grow seem to produce their tomatoes at most 3 or 4 feet high. However my Yellow Pear tomatoes set tomatoes on most of the 14 foot tall plants.

I'd suggest in the future you not do the "touch more" fertilizer..

I didn't say I don't like indeterminate varieties - I love them.

Sorry Adam, I have no means of knowing how you feel, only what you say, and you said "Great Tomatoes, but too tall". I believe you had in mind their growing habit.

There are about 10,000 cultivars of Tomatoes to choose from, some are determinate, others are not. Their taste doesn't depend on how tall they grow, it depends on the cultivar. You should find determinate variety that suits not only your taste but also your growing conditions. You simply don't have enough room in your boxes for growing big sized plants.

windberry, you say "You simply don't have enough room in your boxes for growing big sized plants". According to my experience, untold websites, and many books, I've got enough room. It's certainly not ideal but it works really well. You can have 10 sq/ft per plant, but my question still holds.

You quoted the title of my post. Did you read the content? I was just wondering what people do when the plants get higher than the given support.

^^^ Wonder no longer as for me.......Once my tomatoes reach the top of their 8' rebars I just let them bend over as gently as possible so as not to kink the vines. Any late forming tomatoes can ripen as the vines grow downwards, but the main problem (here) is the resulting sunscald on the fruits due to inadequate shade. Plus these late fruits are on the smallish side and I prefer nice sized slicers. To remedy this problem I start later tomato plants from seed in early June to insure picking good quality tomatoes in the autumn.

Exactly. As I said before, when my cherries vine over the top of my trellis, they just drape down onto the other side. They do that pretty handily, without breaking or damaging the stems. As such, you can have cherry tomato vines that are twice as long as your trellis is high with zero work. You do nothing. They do it all for you. Of course you will get some self-shading, but that's the breaks.