Garden Q&A

Fatty, Fatty, two by four

February 17, 2011 

As a plump child, I heard all sorts of taunts about roundish people. Back then we didn’t know an epidemic of that condition was right around the corner, or half century to be more precise. In an age that reveres models and basketball players, we’re even more unlikely to hear “the wider the better.” But when it comes to digging a hole for a plant, wide is exactly what we’re shooting for.

The chlorophyll molecule in green plants gives them the remarkable ability to take sunlight and turn it into sugars, sustaining all life on earth. And as a fortuitous side effect, the process of photosynthesis also uses carbon dioxide and releases oxygen.

Although plants don’t trot around the block, they, just like us, do have energy needs. To bring water and nutrients into the root hairs and send that liquid to each twig, leaf, and bud takes energy. To transport the carbohydrate-enriched fluids from green leaves to each and every cell in a plant takes energy. Plants get their energy by the exact same process we do. They burn carbohydrates through cellular respiration and use oxygen in the process.

It’s peculiar, but plant roots absorb the oxygen they need from pore spaces in the soil. Openings in leaves are their conduit for carbon dioxide, but since many plants lose their leaves in winter, the root system delivery of oxygen can go on 24/7. As you go deeper in the ground, less oxygen is available in the pore spaces between soil particles. Trees and shrubs planted too deeply in the ground simply can’t get enough oxygen to grow up to be big and strong.

The hole you dig should be no deeper than the root ball of the new oak or camellia you brought home from the nursery. If you dig like a Jack Russell Terrorist going after a mole, you’ll have to backfill to get the correct depth. Holes dug too deeply then filled back to the correct level tend to settle. The soil sinks, the root ball sinks, and the available oxygen goes down, too.

I guess by now you’re wondering what the heck my being a plump child has to do with digging a hole. You’ve gotten the drift about having the correct depth so let’s move on to width. The feeder roots which absorb water and oxygen are in the top six to eight inches of soil. You want those roots to establish a large network, mining the soil for moisture and nutrients. In a hole at least twice as wide as the root ball, the loosened soil offers little resistance to those delicate hair roots, making it easier for them expand their hunting ground.

You’ve established a comfortable situation for the newest member of your landscape. Keep that soil loose and friable by mulching with three to four inches of pine straw applied evenly and well beyond the drip line. Mulch keeps moisture in the soil from evaporating and protects those delicate roots from extremes in temperature. Keep that mulch a few inches away from the stem or trunk to stave off diseases and rot.

My co-workers at the Clemson Home Garden Information Center have factsheets for almost all your gardening questions. When I get a call I can’t answer, that’s where I go. Why not bookmark www.clemson.edu/extension/hgic/ and find your answers there, too?

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