A Gardening Journal

Today in the Garden of a Lifetime: Variegated Common Reed, Outward-Bound



Variegated common reed is growing like gangbusters since being transplanted from its close quarters: A nursery pot that sat in a water-filled galvanized tub.  That colony of Phragmites australis 'Candy Stripe' was split in two, and each half was planted directly in its own galvanized tub that was partially submerged in the reflecting pool.  Some holes drilled in the bottom of the tubs ensure that the reed receives all the water it needs.


Happy colonies of Phragmites try to expand outward.  The sides of the metal tub prevent the usual mode of expansion when a colony is growing in an earth-bottom marsh: Rhizome growth entirely underwater, in the mud at the bottom of the marsh. 


Instead, the colony has produced what at first looked like lazy canes, which leaned outward and over the edge of the tub instead of maintaining the strict verticality typical of above-ground growth.




These "airborne" runners grew so long that their weight helped them angle downward, in hopes of reaching low enough to touch open water or dirt.  This one has been successful, and has been lengthening underwater all Summer. 


Instead of growing leaves from its nodes, the rhizome grows roots.  But it's so buoyant that it can't sink deeply enough into the water for the roots to touch bottom.  Buoyancy isn't normally a problem with rhizomes, who would be growing underground the entire time.  Any normal soil will be heavy enough to hold the rhizome underground, and especially in the case of plants growing aquatically, where the soil is even heavier because of saturation with water.  So there's no benefit to an underground rhizome if its structure is unusually dense—nor a downside if its structure is unusually light.  Indeed, a light structure is almost an advantage, in that it takes less material, and therefore energy, to grow it.  The rhizome can then penetrate into the soil more quickly and widely.   


But buoyancy is a problem, as here, when the rhizome isn't soil-bound at all.  The roots themselves are attempting to bridge the gap, growing downward inch by inch.




Because this colony is growing in a reflecting pond with a rubber liner, even if the roots were able to extend all the way to the bottom—about another foot of growth—they wouldn't be able to anchor there.  The liner is impenetrable.


Phragmites australis is extremely hardy, so Winter survival of these runners even when only very shallowly submerged would be expected.  Who knows how long they'll grow in their effort to locate open earth, so the roots, and then the runner itself, could finally plunge underground.  Because this lined water garden doesn't have any open earth, would the rhizomes grow entirely aquatically, floating in the water and sending up vertical shoots?  Could the rhizomes branch and interweave enough to form a stable underwater mat, and so produce a dense cluster of above-ground stems similar to that arising from the mother colony within the tub?  Then I wouldn't need the tubbed portion—let alone the tub—at all. 


Or is the best choice to sever these outward-bound rhizomes, and keep the colony tub-bound?


The long-term habit and look and even location of my two colonies of 'Candy Stripe' phragmites are still a matter of conjecture. 




Here's how to grow this tough and colorful aquatic grass.


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