Volcanoes and meatballs

11 November 2009

In The Garden With the Fluvanna Master Gardeners
By Irene C. Burke - Fluvanna Master Gardener
Fluvanna County Extension Office: 434.591.1950

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A trees foundation enveloped in mulch, shrubs rounded to a thin green film — both may be esthetically pleasing to some, but are crippling to their victims.

Only topiary absolves you of such gardening transgressions; for it is the fanciful art of sculpting trees, shrubs, and sub-shrubs. Horticultural artists typically choose cultivars of arborvitae, bay laurel, boxwood, holly, myrtle, or privet to express their topiary creations. Worthy candidates make compact growth with dense evergreen foliage. They withstand repeated shearing with few adverse effects.

However, shrubs trimmed and shaved because the narrow ground they inhabit no longer fits, should be relocated to a roomier place where they can relax in their mature width and height. Prune to bring light to the plants interior, paring away aged or diseased limbs, suckers and vertical "water spouts".

Frequent clipping and cutting lead also to a profile of knobby knees and bare ankles about the shrubs lower levels. To encourage lush regrowth, prune by one third each year for 3 years, until the natural form is revealed. For a hedge, create a broad base with a narrower top.

Remove foundation plants that are too close to a structure, by as many feet from center, as the full-grown ornamental requires, or relocate entirely.

The natural habits of shrubs evoke images of feathery down, corkscrews, cascades, and vertical sprays, so instead of shaping shrubs to look like meatballs think fluff, drapes, spirals and points.

Our wild shady woodlands make no volcanoes of leaf litter or pine straw; a trees trunk-flare will extend its roots across the soil then dip below, often embracing boulders and decaying logs. There, the chipmunk, mouse, and vole confine their feeding to emerging shoots, bare new roots, nuts, mosses, seeds and other bits about the forest floor.

The manicured mulch volcano on the other hand, serves as a cozy nest for the same nibblers. These vermin will girdle a tree as they feast on tender bark, and then finish the job at the trees sweet hairy rootlets, hidden by that same dense litter.

In their search for oxygen, water and sustenance, roots will also grow into the thickly layered mulch, slowly encircling then strangling the entire tree. Theres your cankered, starving wood!

Now, mulch volcanoes have as their true purpose, weed suppression and reduced compaction from mowers and human traffic. It would be a far better thing to protect your trees with groundcovers like ferns, mosses, liriope, Creeping-St.-Johns-Wort (Hypericum calycinum), hellebores or sedges, or if you must, mulch lightly from the outer edge of the trunks flaring roots to the drip-line — the point where the tree canopy ends.

A low growing turf will do, but only if you do not injure root flares with mechanical trimmers. Injury at ground level invites disease and pests to the open wounds.

Avoid, too, the modified volcano — a steep sided bowl; reminds me of Crater Lake with a tree stuck in the middle. This invention drowns the trunk flares and suffocates the extended roots, making the tree ripe for toppling in a windstorm.

Rake away the mulching eruptions. Banish the buzz-cut to the barber. Let your landscape breathe.

Tip of the Week

At the Diversitas (2009, October 14) conference in Cape Town, South Africa experts said the world will miss the 2010 target to stem biodiversity loss. In your garden, diversity means greater plant vigor and more disease and pest resistance; so release your garden from boring rows of the duplicate flowers, shrubs and trees.