Leaves have ways of positioning and orienting themselves for maximum exposure to light. From what I have observed, they do a good job of that even with a dense canopy of foliage. As the sun moves across the sky, different sets of leaves get the advantage.

No doubt there is a limit beyond which the principle of diminishing returns takes over. Unless the crowding is truly excessive, which means they were planted too closely in the first place, I would leave them to their own devices. I believe sufficient spacing (which is quite close for beans) and thinning, when necessary, are very important to good yields. I don't believe excess foliage can harm production if the plants themselves have sufficient spacing.

But all of that is one man's thinking, which may be worth nothing to your neighbor. :>)

Jim

My first thought, when reading the original post, was that the description of the beans reminded me of excess fertilization - which is a common mistake with beans. Either that, or as Jimster has suggested, possible over-crowding.

There are only two reasons that I would ever trim foliage from beans:

(1) To prevent disease in wet years, or lessen its ability to spread, by increasing airflow.
(2) To stimulate regrowth in "tired" beans.

The thing is, both of these problems can usually be avoided in the first place by greater spacing. Pole beans, especially, are very adaptable; if planted further apart, they will branch out to fill the space. I have found that 6" spacing for the less vigorous varieties, and 12" for the more rampant (after thinning) produce the best results.

Now, there is one more possibility, which is:
(3) To stress the plant into ripening its fruit, as is done with tomatoes by pinching back the foliage.

I'm assuming that we are talking Canada here? This may be an effort to speed up pod set. But if so, then I am not sure it would be necessary; my climate is very similar to Toronto, and beans have plenty of time to ripen here. For shell beans, it might be beneficial... but not for snaps.

So the bottom line is, unless the plants are unhealthy, there is no reason to trim the foliage. If you pinch off foliage from a healthy well-spaced bean plant, it will just put out new leaves and/or runners.

Agreed with Jim and zeedman.Input from me for this is that if there is too much N in the soil the plants will go into leafy vegetative growth and will not produce enough fruits or not at all.In this case removal of shoots and leaves may help.Having said this, I usually remove leaves from the stems up to 1 foot from the ground level as the vines start flowering.

Zeedman, since you brought up the subject of excess fertilizer for beans, is there a thread where you discuss what you do about fertilizer?

Drloyd, the relationship between beans, inoculant, and fertilizer (particularly N fertilizer) has been discussed at length on several threads. Jimster & I have a running conversation on the subject for the past two years... and with Gardenlad, who I wish was still involved. One of the better threads is linked below, and there is yet another link (regarding soybeans) contained within that thread.

For many years, I recommended the use of inoculant only for legumes, without fertilizer. It was my belief then - based upon anecdotal evidence & a few government reports - that legumes thus treated would produce all the nitrogen they needed, once the nodules were fully established. For some legumes, that may still be true.

But several things since have given me cause to question that conclusion.

One was my inoculant experiment last year, which while not fully conclusive, was not encouraging. Of the several legume species that I tested, only cowpeas showed a noticeable improvement when treated. This was confirmed again this year, when I rogued out several young cowpeas last week, and found the 6" plants already heavily nodulated. Suspecting that this ability to benefit from inoculant might extend to others in the Vigna genus, I heavily inoculated adzuki beans (Vigna angularis) this year. Pulling one up this week in the name of science, I found it heavily nodulated as well. I will try to post photos soon.

Another influence for my change of opinion was a recent thread (I believe it was here on GW) that contained a link to a report on nodulation of various legumes. According to this report, common beans are some of the least efficient at developing nodules; and even when treated with inoculant, may not produce enough usable nitrogen to supply their needs. Observations by myself & several others, as to the scarcity of nodules on bean roots, seem to confirm this. This would explain the yellowing or weakness of bean seedlings observed by so many gardeners.

So what about fertilizer? Beans will perform well without either inoculant or fertilizer, but they may not perform to their full potential. As a rule, weaker plants are more susceptible to disease, insects, and environmental stress. Sometimes what appears to be a disease problem, is in reality caused by a nutritional deficiency.

The effect upon beans of over-fertilization is well established. They may not produce as much N as other legumes, but what they do produce still makes them sensitive to the presence of excess nitrogen. Lush foliage with little to no beans one of the most frequent complaints, and upon further examination, the cause is nearly always too much N applied to the soil.

For my own part, I once dug in large quantities of horse manure to a previous garden, in the 80's. Although I did not notice it then, in retrospect my beans were very heavily foliated, and slow to bloom. I suspect that only as the nitrogen began to be depleted, halfway through the season, did they begin to blossom... but then bore well.

It would seem logical that there must be a happy medium, somewhere between no fertilizer, and over fertilization. Given the differences in soil type & fertility, this would likely vary by location.

It might even vary by variety, and I wonder if other species in the genus Phaseolus share the poor nodulation of P. vulgaris. If I can, I'll sacrifice a plant each of P. coccineus and P. lunatus for comparison.

The recommendation that I make now is for a light application of N to common beans at the time of planting, with no further fertilization. Other legumes - particularly peas and Vigna beans - may not need this. It is too late for me to perform an experiment this year, but next year I will try to find some scientific proof that early fertilization is beneficial to beans.

Here is a link that might be useful: Yellowing of beans

Thank you Zeedman. I am still trying to figure out why my bean plants in self watering containers in the greenhouse are so much larger and more robust than the plants out in the garden. And some outdoor plants are still chlorotic.

Our mid-summer night temperatures average only 52F. That probably does not help. And testing with one of those home kits indicates that our soil is ok in P and K but low in nitrogen.

I will continue this on the yellowing of beans thread.

For those who did not see the link on nitrogen fixation that Jimster posted, here it is again.

Here is a link that might be useful: Nitrogen Fixation