Plant roots defy na­ture to feed on com­post nu­tri­ents

Bray People - - LIFESTYLE -

PLANT roots nor­mally grow down in the ground. In the nat­u­ral world, there are nearly al­ways ex­cep­tions to ev­ery­thing and so it was dur­ing the past week I saw an ex­am­ple of roots grow­ing up­wards rather than grow­ing down in the ground.

First the sci­ence bit. Roots don’t ‘ know’ that they are sup­posed to grow down. They don’t have a mind, a brain or even a ner­vous sys­tem. Much of what plants do is sim­ply chem­i­cal re­ac­tions con­trolled by the laws of physics.

Plant hor­mones are nat­u­rally oc­cur­ring sub­stances that af­fect the be­hav­iour of cells and aux­ins com­prise the group of plant hor­mones that cause plants to grow. Cells have re­cep­tors for par­tic­u­lar hor­mones that cause them to re­spond in par­tic­u­lar ways to ex­ter­nal stim­uli like grav­ity, light, touch, the pres­ence of wa­ter and nu­tri­ents, and so on.

There are spe­cial plant cells with tiny bod­ies in them called sta­toliths. These sta­toliths have starch grains in them. The starch grains make the sta­toliths ex­tra heavy. In re­sponse to the pull of grav­ity that makes the sta­toliths sink and con­se­quently they get con­cen­trated at the low­er­most tips of cells.

Aux­ins act in part­ner­ship with the sta­toliths and since the sta­toliths are al­ways con­cen­trated at the low­er­most tips of the plant’s cells, growth is con­cen­trated there re­sult­ing in roots grow­ing down fol­low­ing the pull of grav­ity.

I was think­ing about these mat­ters as I was emp­ty­ing the com­post clamp in our gar­den. The com­post clamp is a sim­ple con­trap­tion: four re­cy­cled tim­ber pal­lets stand­ing upright on the soil held to­gether at their cor­ners by heavy duty ca­ble ties to form a secure box open top and bot­tom.

Plant wastes, kitchen scraps, plant trim­mings, au­tumn leaves, some grass cut­tings, etc., all get thrown in. They rot and de­com­pose over time. When the clamp is full it is rested for a year and a new one is started. Old clamps are emp­tied in spring­time and the an­nual mir­a­cle un­folds as the mot­ley col­lec­tion of for­mer waste emerges as the sweet-smelling, very dark brown, sticky but crumbly black magic that is gar­den com­post.

Fi­nally, to get back to my orig­i­nal point, emp­ty­ing the bot­tom of the clamp re­vealed roots from a nearby tree grow­ing up­wards into the com­post. Pre­sum­ably, in its never-end­ing quest for wa­ter and min­er­als, the tree’s re­sponse to the ex­cep­tion­ally high con­cen­tra­tion of nu­tri­ents in the com­post was over­rid­ing the nor­mal re­sponse that makes roots grow down, caus­ing them to grow up­wards in­stead.

Well-rot­ted gar­den com­post is a great source of nu­tri­ents for plant growth.

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