Roots on a plant?

Question

My kids say that the science teacher told them the roots on a plant are as long as the plant is tall. Assuming that is correct, if you cut the top of the plant, do the roots shrink?

Answer 1

There is nearly as much root underground as plant above ground, depending on the plant. But generally, for large plants like trees - the root spread laterally, rather than going down as deep as the tree is high. The roots of a tree can extend as far to the side of the tree as the tree is tall - way past the drip line of the canopy.

If you cut off the top of a plant, the roots will only shrink and die if they don't have enough energy to try re-growing the top of the plant.
Generally, they will not "shrink", just try and grow new tops to repair the damage.

Answer 2

I have heard this from a middle school science teacher too. I think this is a great myth going around in the science teacher world. Like many of your responders have said, I think it depends on the plant. There are certainly many plants that do NOT fit that rule. And if you were to cut a plant, its roots do not just shrink and go away. When you prune a plant, it often times stimulates growth, both in the canopy and the roots. So, I would tell your kids that that may be true some of the time, but it's a BIG generalization.

Answer 3

OK -- first, it depends on the type of tree. Many trees grow a "tap" root: this root greatly enlarges to become the most prominent root of the plant and is known as a tap root. Many smaller branch roots may grow from the tap root. This can often be an extremely long root. Other trees have a "fibrous" root system: numerous roots of more or less equal size. These roots are adventitious which means they can grow from plant organs other than roots e.g. stems.

As stated by others above, cutting the top does not cause the roots to shrink, it just causes the tree to attempt to form a new top. It is the opposite that is true -- if you cut the *root* without trimming other parts of the tree in equal proportion, parts of the upper part of the tree will die.

Therefore, when you do bonsai, you first trim the roots, then the tree, in equal parts, when transplanting and shaping.

Answer 4

It depends on how you measure the roots to compare them with the rest of the plant. It may be true to some extent for some plants, but certainly not all. You can find this out for your self quite easily by planting a few easy to grow seeds like sunflowers.

Answer 5

That is not true. I have never seen a 12 foot root on my giant sunflowers. On the other hand, the roots on my wisteria are many times longer than the wisteria is tall, and it has never been pruned.

Answer 6

Eventually that's why banzai works.