By Marie Narlock >> IJ correspondent

Gardening myths are common and hard to shake. Most of the time, these old wives’ tales are harmless, but sometimes they offer false hope to gardeners.

Take the misconception about adding coffee grounds to the soil to increase acidity for growing camellias, hydrangeas and azaleas. As it turns out, fresh coffee grounds are acidic, but used coffee grounds are not. So to change your soil’s pH using coffee grounds, you’ll have to rob yourself of a cup of coffee. Ouch.

Same goes for amending with banana peels to add potassium for plant growth and flower production. Unfortunately, this can lead to problems. First, it takes nitrogen to break down the peel, which means less nitrogen for greening plants. Second, putting peels in shallow soil may invite unwelcome wildlife. Think rats, skunks and opossums.

While we’re at it, how about adding eggshells to the soil for calcium? Unless eggshells are ground into a fine powder and put into an acidic solution, the calcium stays intact — for a long time. How long? Undecom

posed eggshells have been unearthed at archeological digs.

Then there’s the suggestion to put human hair, human urine or Juicy Fruit gum in gopher holes to nab pesky gophers. If only this worked! Then there would be a sea of gardeners unzipping, clipping clumps of hair and lining up at vending machines. Alas, there’s zero science-based evidence that this works. Plus, do you really want to add gum to your soil?Or how about spraying shrubs with dish soap to eliminate aphids? Unfortunately, this one can do some harm. Most dish soaps are detergents, which means they strip oils and fatty substances called lipids from man-made surfaces. Leaves are not man-made surfaces, but they’re covered with a layer of waxy lipids that protects them from water loss and diseases. Detergents can strip this protective layer, causing damage. Better choice? Avoid damaged, crispy-crunchy leaves and simply knock aphids off with a blast of water from the hose.

Same goes for vinegar for killing weeds. Because of its high acidity, vinegar might nail some annual weeds, but it’s unlikely to translocate downward. Translation: It won’t get down into the roots. That means it will be ineffective for perennial weeds. Worse? If you keep adding vinegar to your soil, you might end up over-acidifying it, which will affect what you can plant there. When it comes to your soil, it pays to think like a doctor and “do no harm.”

Or what about braiding spent daffodil leaves? Who hasn’t gotten rubber bands out to cinch those babies up after the flowers have died back? This common mistake reduces photosynthesis. Leaf parts not exposed to the sun can’t turn sunlight energy into stored chemical energy, which lessens the production of new leaves and flowers next season. Oops.

Here’s the good news: most of these gardening misconceptions are harmless or fixable — goofs we’ve all made, often on the recommendation of well-meaning friends or neighbors. We learn. We move on. As the saying goes, we don’t sweat the small stuff.

What really matters is the bigger picture. The biggest myth of all is that your garden is not part of the broader environment.

It is.

And because of that, your choices matter.

Choose plants naturally adapted to your area: wispy grasses on the coast, heat-loving sages inland and native currants and strawberries in damp forest locales. Protect our dangerously dwindling population of insects by turning off outdoor lights at night and growing plants that welcome them. Avoid pesticides and synthetic fertilizers that pollute our air and water. Reduce or replace lawns to save water and energy that leads to greenhouse gases.

In the end, tossing a handful of used coffee grounds into your soil is not a big deal. Same with braided daffodils. But there’s no mythology about how best to manage our gardens to keep them and the surrounding environment healthy and thriving.

Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provides science- and research-based information for Marin home gardeners. Email questions to helpdesk@marinmg.org. Attach photos for inquiries about plant pests or diseases. Please call 415-473-4910 to see when a master gardener will be at the office or drop off samples 24/7 in the sample box outside the office. To attend a gardening workshop or subscribe to Leaflet, a free quarterly e-newsletter, go to marinmg.ucanr.edu.