What is a Sucker?

The roots of many plants and trees never see the light of day, and spend their lives pushing ever downwards and sideways in pursuit of moisture and nutrients. The roots of other species however will occasionally send up suckers, or shoots, that grow up and through the soil to develop — if undisturbed — into fully-grown plants with their own root system. The jujube tree is a well-known example of one such species.

Why Do Trees Sucker?

Suckering enables a tree to reproduce itself vegetatively (asexually/by cloning itself) across as much land as its roots can spread. The parent tree may die, but its suckers ensure its genes live on, and often many metres away. (Note that this vegetative reproduction does not apply in the case of grafted trees — here it is the rootstock, genetically different to the tree, that propagates its species by suckering. Rootstock suckers develop into trees of the same species the rootstock originated from.)

Suckering can also be a survival mechanism. The above-ground portion of a suckering species may be destroyed by fire or physically removed, but its below-ground roots usually survive and send up replacement shoots. Disturbing the roots of some species, including jujube, can in fact be a stress signal which increases the amount of suckering.

The World’s Largest and Heaviest Organism is a Suckering Tree!

I had to slip this fascinating factoid in as it’s too good to not share!

‘Pando’ (Latin: I spread out) is a massive colony of identical male quaking aspen trees in Utah, USA, all from one giant subterranean root system. Pando spreads over 43 hectares, weighs about 6 million kilograms (6,000 tonnes), and its root system is believed to be over 80,000 years old (not a typo!).

On Suckering

Having spent the last two weeks underground exploring root anatomy here and here, let’s now follow a suckering root as it produces a shoot en route to the sky. It may help to re-read those two previous posts, as well as refer to these excellent diagrams also previously linked to.

Adventitious Buds

The meristem tissue in plants functions like our own stem cells, in that it is able to differentiate into any other tissue or organ, given the right inputs. Shoot apical (apex) meristem produces all above-ground tissue such as shoots and leaves. Root apical meristem differentiates into specialised root tissues such as the epidermis, cortex, and vascular cylinder/stele.

An adventitious bud, whether on a shoot or root, is one that develops in an unusual place, ie not from the apical meristem. Adventitious buds on shoots help a plant recover from injury, by driving the healing of wounds or the development of replacement branches. Adventitious buds on roots develop into suckers.

Sucker Shoot Development

The adventitious sucker bud arises from the pericycle, which makes it an endogenous structure, one developing from within deep tissue. This contrasts with the more familiar axillary buds found within a leaf and stem intersection, which are exogenous (external, outside).

At this early stage the bud is merely a small bundle of meristem tissue, and without the connection to the vascular (transport) phloem and xylem tissue that exogenous buds have. An apical meristem later forms at one end of the bud, from which young leaf tissue develops. Vascular tissue develops at the other end and connects with the root’s vascular tissue.

The bud may continue to grow over a few years. More leaf tissue forms and wood is laid down during this time, until eventually the bud is a fully-formed shoot which pushes its way through and out of the soil.

Post-Shoot Development

Unwanted suckers are best removed when small and young so as to not compete with the mother tree, and with as minimal soil disturbance as possible — mowing  or cutting with secateurs at ground level are common methods. Be especially careful when removing any suckers that are very close to the mother tree’s trunk.

Suckers can be severed from the mother root if wanted as separate trees. Dig gently down to where the sucker is attached to the mother root, and sever this on either side of the sucker, making sure there are enough roots on the severed piece to sustain the sucker.