Friday, September 16, 2016

The Weekly Weeder--Oxalis corniculata: the weedy oxalis

        I once thought that I would grow Oxalis corniculata, creeping wood sorrel, as a lawn cover, as it stayed green and growing in a drought year in the mid-‘80s when we stopped watering to fish in the river.  Dad was very upset to come back from working in Nevada for two years to find his grass dead and common oxalis dominating his lawn. 
Thirty years later, it still dominates his lawn, though the grass helps hide it.  But I don’t think it would ever have grown thick and even enough to make a good lawn, and its seed pods, held up erect on top, are not pretty, ½-3/4 inch long and turning dull yellow as they ripen and tan after opening.  

Ornamental Oxalis

There are other oxalis that are big, pretty, clump rather than spread, don’t show off their deadheads, and just show up here and there by seed, bulbs, or root buds.  They come in various colors, patterns and growth habits. Oxalis all have the same kind of leaves with three heart-shaped leaflets, and ½-inch five-petaled, funnel-shaped flowers, usually white or pink in the ornamentals.  The big ornamentals are also deciduous, dying down in the fall and sprouting in late spring.  Creeping wood sorrel stays green all winter and sprouts any time of year, blooming mainly in the summer.

Young clover and oxalis in 4 x 8 sand path.  Clover has larger, round leaflets, sometimes with a chevron mark.

These are also known as shamrocks, named such by florists, who know how to sell a plant.  The “true” shamrocks of Ireland are just white clover.  Clover leaflets are not heart-shaped, but they often have a white or red chevron within their leaflets.  Clover leaf veins lie in parallel lines radiating up and out from the center vein, forming chevrons opposite the colored chevrons; oxalis leaves have serpentine veins radiating from the base of the leaflets.

Red oxalis blooming and seeding in small sedum.  There are some dark seed pods to the upper left

O. corniculata has small leaves rising from on trailing stems and grows green or burgundy red, with slightly smaller yellow flowers than the larger oxalis.  Getting rid of it is not easy.  It not only spreads by seed but by crawling on the ground, though it does not root from stems unless it is broken off the main root, in my experience.  It has a tap root that can be pulled after being loosened with a knife or scissors.  It produces a lot of seed that probably stick around for many years. 

Creeping Wood Sorrel seed pods

At least it takes a few weeks for its seed pods to ripen and pop, and they don’t throw them in your face when disturbed, like bitter cress, but they do throw them up to 10 feet when they pop.  If you don’t heed the blooming of the flowers, you have the pods to catch your attention.  But I have never been so in control of my parents’ yard that I could spend the time it takes to kill it in the lawn.  Actually, I’ve never cleared it completely from any property, it is so persistent.
Like most weeds, the only reason to kill it is that it messes up the view if it is allowed to take over, and it easily takes over.  It stays low for the most part, but is quite capable of climbing a foot on other plants.  What makes a garden look good is repeating masses of colors and textures of different plants, and plants that invade those masses makes it look messy.
Gardening is keeping order in the landscape, eliminating disorderly plants and keeping even desirable plants in their places:  for freedom of movement; beauty; and sometimes growing food and medicine.  One can garden by weeding alone; one cannot garden without it.  You get to decide what is and isn’t a weed, and many of them will eventually show you that they are.
Rycke Brown, Natural Gardener          541-955-9040