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Does pruning encourage root growth or root decay?  RSS feed

 
Ben Bishop
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Hey all,

Quick question I've been pondering lately. Regarding nitrogen fixing plants, we often hear about how pruning the branches causes roots to decay underground releasing nitrogen stores to the soil and the surrounding plants. That makes perfect sense to me but I run into problems when I hear things about how when you prune/pollard/coppice trees or cut raspberry canes to the ground etc, you cause them to grow stronger the following year. I would imagine that this is because the plants energy gets redirected to root growth.

So my question is, what are the main factors that determine whether a plant will become weaker and having its roots decay from cutting it back or grow stronger? Is it just differences in plant genus/species? Is it time of year? I imagine the answer is "it depends" but I want to try to get specific here. Thanks!

 
Terri Matthews
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Location: Eastern Kansas
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According to one rancher, when the corn eats the top of the grass then the grass drops off some of the roots, as the newly shortened plant no longer needs this much root. So the roots are not being lost to diseases or anything, instead the plant is doing it for the plants' own benefit.

He made it sound like cut and come again greens: I pick a fistful of leaves ans the plant grows the leaves back again. The plant that produces the greens does not get weaker at all: it just grows more slowly than the plant I did not give a "haircut" to. I think the roots do the same thing.

AFTER the plants has gotten rid of the roots of course they will decay, as those roots are no longer alive.
 
Ben Bishop
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Terri Matthews wrote:According to one rancher, when the corn eats the top of the grass then the grass drops off some of the roots, as the newly shortened plant no longer needs this much root. So the roots are not being lost to diseases or anything, instead the plant is doing it for the plants' own benefit.

He made it sound like cut and come again greens: I pick a fistful of leaves ans the plant grows the leaves back again. The plant that produces the greens does not get weaker at all: it just grows more slowly than the plant I did not give a "haircut" to. I think the roots do the same thing.

AFTER the plants has gotten rid of the roots of course they will decay, as those roots are no longer alive.


Thanks, this was my understanding as well. My confusion comes with the one line you said about the plant that was growing more slowly due to pruning off the leaves/branches. I've heard people say that pruning the plant actually sends energy that would have been directed towards maintaining that part of the plant now can be used to grow even MORE roots and make the plant better off for it. Although I assume you have to do this at certain times of the growing season.

MAYBE what people mean is that if you prune your perennials right before spring you allow for really strong new growth because the plant has this big root system and not a lot of above ground parts so it produces really healthy growth? And then conversely if you prune a perennial in the middle of the growing season, whether it's a nitrogen fixer, fruit tree, whatever, it actually drops off it's roots to match it's above ground parts?

I think this is an important thing to get right because we want to find that sweet spot where we can harvest a lot from our plants by way of leaves, fruits, flowers, stalks, etc but time it right so that we encourage the plant to grow even stronger the next season.
 
S Bengi
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Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even distribution
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1) If you prune of the flower buds aka plants that fruit mainly off last years growth. The all the energy that normally goes to the fruit production will go straight to growth, so you will see more growth.

2) Some plants will die/stagnate if you allow them to flower/fruit perennial collard, but if you prune off the flowers it will keep on growing for another, up to 9 or 10, alot of grass will follow a similar route.

3) Serious pruning induce bonsai like dwarfing but mild pruning induces watersprouts that have huge space between the leave nodes, I can only assume that is to help it get out of the reach of whatever herbivore it is that is eating it and then harden off before it comes back next year.

4) If a plant is "root-bound" and you prune its "leaves" thus it roots, and it is no longer root-bound you will get a flush of wonderful growth.

5) If you are pruning both a "productive grass/tree" and a Nitrogen fixer together, then the Nitrogen fixer will release extra nitrogen into the soil that the "productive grass/tree" will absorb and increase it's growth.


Too much pruning or improperly time pruning/grazing can damage a tree/grass.
 
Terri Matthews
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Location: Eastern Kansas
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Ben, yes, that was pretty much what I was saying.

Ideally roots and tops are in balance: the top sends nourishment down with phototsynthesis and the roots send water and minerals up.

If half the top is gone (harvested or eaten) then less roots are needed and the plant cuts off some of the roots, and also grows some of the top back. That is how the plant uses the available energy. The roots that have been cut off from nourishment die and decompose.

If half the roots are gone (say cut by a shovel) then the plant uses the available energy from the phosynthesis to grow more roots. Meanwhile the growth of the top slows a great deal, as it is getting less water and minerals.

So if half the top is removed the plant tries to get the top and the bottom balanced, and if half the roots are removed the plants will again try to get the top and bottom balanced.
 
Ben Bishop
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Thanks Terri, that makes sense now. Would this hold true for things like coppicing or when you cut raspberry canes down to the ground? It seems to me like when you cut off ALL of the above ground parts of some plants they will actually re-grow to their original size much quicker than before. They must not get rid of as much of their below ground parts
 
Peter Ellis
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Location: Central New Jersey
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Complicated question to which I do not know the answers. I am sure that in fact plants do any combination we can think of, plus a few.
Some plants respond to pruning with rampant growth, some will die off. Just so many variations. Some prune v roots in response to cutting back the tops, but do they all drop roots? I would wager not all. Plants that reproduce with runners - do they prune roots or push growth on an unpruned top or just grow back fast? I would think self pruning roots would be contrary to survival for such plants.
Lots of variables.
 
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