Well, if you just over fertilize with N then you will get lots of lush green foliage and less fruits. But if you use balance fertilizer and not over do it, everything falls into place fine.
According to some views plants always need/use more Nitrogen than P and K proportionally.

One thing to realize that an established garden soil often has some NPK So when you cut back one via fertilizing , there will be still some in the soil.

Plants have some intelligence too, I think. They pick and choose what to uptake according to their needs. .

Sey

I must say I haven't experienced this with tomatoes, but many years ago I used Alaska fish fertilizer 5-1-1 on a planter of geraniums. The foliage grew enormous and healthy, but there were no flowers. I read about the N thing (I'm sure here on GW) and realized what had happened. I believe I switched to a bloom food and I think I got it to flower at that point.

So not a study, sample size of one, but definitely saw that principle in action. Since then I've used more balanced fertilizers, and I've never seen that effect again.

Buzz Saw, it is a myth. The myth is not a gardening myth.

It is the way you are structuring the question: "Any evidence or studies that high N = Less Fruit? Is this one of those gardening myths?"

The way you pose the question seeks steadfast rules yet does not define "how much is too much", as you pointed out. There are no rules in gardening, though black-and-white thinking like this is not suitable for generalization. What is appropriate for your plant depends on its genetics and growing conditions. Gardening does not have the same playbook and rules of thumb can be useful but sometimes just wrong when misapplied in situations that were never intended.

Your question relies on the following logical fallacies and psychology:

1. False Dichotomy

2. Placebo effect

3. Instant Gratification

4. Loaded Question

The "myth" is based on some truth, such as limiting the application of nitrogen determined under specific growing conditions causing the onset of fruiting sooner. That when done properly usually increases yield, since you get tomatoes sooner and plants get beat as time goes on, so earliness is usually desirable. Applying "too much" nitrogen later is undesirable to farmers, because it is a waste of money. The plant has a certain capacity and even if it is swimming in nitrogen, it still is only one man... errr.. one plant ;-) Marketers take advantage of this psychology by exploiting trust and the unfamiliarity of aspiring gardeners on the nature of cause and effect (which experienced gardeners invest in to learn) to push their miracle products, so the more confusing it is out there the more they expect to sell.

So in gardening the first rule is that there are no rules, except maybe the need for common sense, and to develop the skill in your plot or containers with well-informed trial and error approaches.

PC

Just from personal experience I would say yes. A few years back I accidently fertilized my potatoes with some left over hayfield fertilizer. I thought it was 6 24 24. The tops of the potatoes got like 4 ft high and probably as wide but few to no potatoes.

Another way to look at it is in regards to feeling a need to add N and being uncertain about how much. This ignores the reason for adding N in the first place, which is an attempt to fix a problem, and you don't say what problem you are trying to solve by risking the creation of this new problem.

One will never know why one gets fewer tomatoes from a particular crop as it's a different set of conditions from all previous crops. A controlled study done in some other part of the world will do you not one bit of good. Also you are most likely in a different climate than everyone else here, so there is no simple logical way to answer your question. YMMV

I don't fertilize because unless you're practicing depletion growing (not gardening), fertilizer is a rip. Although they often occur together, lush green foliage is NOT a sign of poor fruiting. Well, maybe if one loads on lots of chemicals...

The short answer is YES. Giving a plant too much nitrogen will result in a weak, lush plant with few flowers.

Also, plants that are over fertilized will attract insects more than one that is not.

Just about every university ag extension says that excess nitrogen results in fewer fruits and flowers. So you could conclude, I suppose, that these ag extensions are just propagating myths. Seriously, just do an online search for the terms "too much nitrogen" and "extension", and you'll pick up loads of those.

Of course, you can dig out the individual research papers -- "actual studies", or you could trust the ag extensions to inform you truthfully about them.

One more thing that I forgot to mention in my previous comment (maybe more than one)

Tomato plants keep growing (foliage) continuously. It is not like vegetative state ends at time "T" and sexual state (fruiting begins) begins. So for this reason they need N all the time AND perhaps more of it to support a massive existing foliage. It is like a heavy set person who would need more food. As long as there is no "P" and "K" deficiency a little bit extra "N" is not going to cause a problem.(in my view)

I have read some strong arguments for a 3-1-2 NPK ratio. part of the reasoning is as follows :

• N is used in higher quantity than P and K..

• N, being highly water soluble can leach down, away from the reach of plants roots.

• P sticks to the soil and excess of it can last for much longer time.

• Most establish gardens probably have already enough P

• K is somewhere in between, in stability and plants' need

If ever in doubt , I think the old fashion All Purpose fertilizer with a 1-1-1 ratio is the safest rout to take, in the absence of a concrete scientific explanation AND a soil analysis.

However , the contrarian view is that not all the "P" and "K" shown in soil test is readily available to the plants. That is why applying like some "Bloom Booster" can result in quick increase in flowering.

Are you confused ?

Sey

i think it may matter on how slowly released the nitogen fertilizer is, most organic nitrogen is released slowly, so with organic fertilizers a slightly higher nitrogen # i don't think would make much difference.(except liquids like fish emulsion) blood meal being the exception in that it has a very high nitrogen rate. with chemical nitrogen fertilizer i could certainly see it having a negative result. i certainly wouldn't use nitrate of soda on my tomatoes(unless you know to mix with other fertilizers to create a good balance). as a general rule i stay a way from nitrogen fertilizers with higher than a 10, but as far as chemical fertilizers go 10 -10 -10 no problem. most of the time i'd say though large plants with little fruit is from overcrowding causing lack of sunlight.

Doesn't it make sense to give them fertilizer with more N early in the year and then as they begin to produce blossoms cut back on the N and fertilize with something that has higher P & K?

Rick, that what many of commercial growers do, Calcium nitrate given early on, which is 15% nitrogen.