Clovers not always lucky - some are weeds

I recently discovered what I thought were clovers in my backyard. This discovery led me to research shamrocks, hundreds of varieties of covers and the yellow wood sorrel weed.

Shamrock "weeds" have become a serious problem in some areas. Four-leaf clovers bring good luck but the "three-leaf clovers" mean your luck has run out and these weeds have invaded your garden.

Actually, these weeds are not clovers or shamrocks. They are Oxalis corniculata plants, otherwise called creeping wood sorrel, a group of similar plants hybridized readily that form several subspecies. All wood sorrels and oxalis plants have clover-like or shamrock-type leaves. But do not be fooled into spending hours looking for a four-leaf clover among these three-leaf types.

During my research, I had to identify exactly what was growing in my yard. I picked a leaf, picked a flower, took pictures of both and then started a search through my gardening library and the Internet until I found a perfect match.

It turned out to be yellow creeping wood sorrel weed, or Oxalis corniculata. Leaf colors may range from bright green to dark green, even red or purple. They have extensive fibrous root systems, and all species have small, yellow, five-petal flowers.

The many stems of the yellow wood sorrel hug the ground, sending roots into the soil all along their length. Try to pull up the plant and these slender stems snap off, and the plants continue creeping along.

The only way to successfully remove the creeping plant is to attack it when it is young. Once a plant has aged and spread, you have to skim off the top inch of soil and remove the whole clump as a mat. Young plants often grow unnoticed because the coppery tinge of their leaves camouflages them on the soil.

Oxalis control is difficult because the plants are resistant to most herbicides and they propagate by several methods. Cultivation will eliminate visible plants, but herbicides are usually needed to win the battle.

Plants in turf grass areas can be partially controlled using lawn weed killers containing dicamba, Trimec or trichlophyr (Turflon D, etc.). Add a surfactant, or surface-active agent, to improve wetting and spreading to the herbicide, and spray as often as needed.

The best approach is sometimes to just persuade yourself that the plant is an inconspicuous, perhaps not even bad-looking, ground cover.

The familiar St. Patrick's Day variety, Oxalis acetosella, is often available at florist shops and many grocery stores this time of year. It has tiny, dark green, triangular leaves and grows to a height of about six inches.

This variety hails from Europe, Iceland and Asia. It is not the official Irish shamrock, Trifolium dubium, which is actually a yellow- flowered clover or trefoil. That clover is difficult to grow indoors, so nurseries and florists sell Oxalis plants instead.

So how do you grow these shamrocks? They like cool air, moist soil, except in their dormant period, and bright light. They do not have an extensive root system, so unlike many plants, they actually prefer to be crowded in a container. However, if the plant dries out too quickly, you may need to move it to a larger container.

Fertilize every two to three weeks while the plant is actively growing or flowering, using regular houseplant fertilizer. For application rate, follow directions on the container.

Be aware that no matter how much care you give the plant, at times it will look sick and lose its leaves. This dormant period, which occurs two or three times a year, is part of the growing process.

During dormancy, stop watering. Let the leaves die back naturally, then remove dead, brown leaves. Place the plant in a cool dark place. Plants generally "sleep" for about three months. New green shoots signal that the plant is waking up and needs to be moved back to light and watered again.

The four-leaf white flower clover plant, Trifolium replens, a creeping white-flowered perennial, is considered the original shamrock. It is a universally accepted symbol of good luck with its origin ages old.

Early Celts of Wales held white clover high in esteem as a charm against evil spirits. This tradition was continued by early Christian leaders and became the symbol of the Holy Trinity for the Irish people. One leaf is for faith, one is for hope, and one is for the love you know, and God put in another for luck. If you search, you will find where they grow.

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Debi Papp is a member of the Yuma Garden Club and various other gardening organizations. She may be reached at 783-3189 or e-mail greenthumbs1@roadrunner.com.