Why do tomato plants "give up" branches?

July 8, 2015 5:51 PM

I've grown tomatoes three times now, and have noticed that my tomato plants seem to "give up" certain branches/stems. The affected stems turn yellow and do not flower; if I don't prune them off right away, they eventually turn brittle and snap off the plant easily.

Around the time a stem starts going bad, a new stem can often be seen emerging from the same junction as the yellowing stem. Nearby stems are not necessarily affected, and the plants remain productive as a whole.

The two-stems-from-one-junction thing is consistent with what I've read about "suckers", but a lot of the information I've read on that subject is contradictory. Can anyone give me a solid botanical explanation of what's going on? Does it indicate a problem with the growing conditions I'm giving my tomatoes? Should I be pruning more?

posted by aws17576 to Science & Nature (3 answers total)

I can't give you the botanical explanation, but I can tell you that I've been growing tomatoes for many moons and this is totally normal. That said, if it's happening most with the lower leaves of the plant, it could be a nitrogen deficiency. Add nitrogen if it's early in the season, but not if they're already producing, because then you'll encourage greenery over tomatoes.

I don't prune aggressively. I do what you're doing -- if a leaf starts get get yellow, I break it off and let the new growth come in. Doesn't affect production, so why change anything? The biggest benefit to serious pruning is that you force the plant to produce less fruit (because it has less growth to do so), so the resulting fruit are bigger. Personally, I'd rather have more than bigger.
posted by mudpuppie at 6:47 PM on July 8, 2015 [2 favorites]

I've noticed that this happens on branches where no fruit form. My assumption has always been that the plant just doesn't need those branches, so it terminates them.
posted by OrangeDisk at 7:30 PM on July 8, 2015

So, I also don't have a botanical explanation, but I have some guesses about the overall tomato growth strategy. This is primarily (but not exclusively) a behavior of indeterminate tomato plants, which, given enough nutrients and felicitous conditions, never really stop growing. In the past I've made 6-8' tall tomato cages out of concrete reinforcing mesh, and a healthy tomato plant will happily grow right to the top.

Here's what's happening: You have correctly identified these "extra" branches as suckers. An unsupported indeterminate tomato plant will usually grow until it literally flops over (hence the stakes and cages), and then just keep growing along the ground. These suckers are all potential vertical replacement stems once the plant is in horizontal mode. The nodes and lower reaches of the suckers will also readily grow roots given the right conditions, which is why you occasionally hear the suggestion that suckers pruned early in the season can be stuck right back in the ground to grow extra plants.

I'm of two minds about pruning suckers. I usually remove them within a foot or two of the ground to keep tomatoes from rotting on the ground, but other than that I let them be.
posted by pullayup at 7:42 PM on July 8, 2015 [3 favorites]