Seems like just about everyone has a favorite homemade garden concoction. But which ones help your plants — and which do more harm than good? University of Minnesota horticulture professor Jeff Gillman, Ph.D., put a bunch of old-time tips to the test for his just-out book The Truth About Garden Remedies: What Works, What Doesn’t & Why. Here, he dishes the dirt…

The Claim:

Add eggshells to containers to nourish plants.

The reality: Eggs really are all they’re cracked up to be! They are a great source of calcium, which is especially good for tomato plants. Mix six to 12 crumbled shells into soil before adding it to your planting container.
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The Claim:

Place broken crockery in the bottom of a pot to improve drainage.

The reality: Pieces of broken crockery can actually interfere with the flow of water out of a container. Water doesn’t move easily between potting soil (a fine-textured layer) and fragments of crockery (a coarse-textured layer). Without proper drainage, water will sit on the bottom of the pot and, sooner or later, the roots of the plant will rot. Bottom line: It’s best to fill a container completely with one potting medium that drains easily.
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The Claim:

Grow marigolds to stop insects from attacking your garden.

The reality: Marigolds, like chrysanthemums, contain chemicals that repel bugs. If you plant them around vegetables that are prone to insect damage (tomatoes are a classic example), the flying critters often don’t bother trying to make their way through the flowers to find the vegetables. This method of insect control is safe for the environment — no pesticides are necessary — and insects do not develop a resistance to it.
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The Claim:

Spray mouthwash on your plants to kill diseases.

The reality: Most mouthwashes contain a high concentration of alcohol — enough to control powdery mildew and black spots (fungus) on roses and other plants. To use mouthwash in your garden, create a mixture of one part conventional mouthwash (like Scope) and three parts water, then spray on leaves once a week. But be sure to test this remedy on one leaf first, since the high acidity of the mixture has the potential to burn a plant.
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The Claim:

Play music while applying fertilizer to make your plants grow faster.

The reality: It has been said that sound stimulates the plant to open its pores, making it easier for foliage to absorb fertilizer. No one has provided concrete proof that the noise actually makes plants mature faster, but rumor has it that the green things are fond of soft, elevator-type tunes.
Rating: The jury is still out.

The Claim:

Pour vinegar on weeds to get rid of them.

The reality: Heavy doses of undiluted vinegar, like white or apple-cider, tear through anything — but it will only kill the parts of the plant that are directly touched (in other words, not the roots). Thus, weeds may grow back. Still, you can use vinegar as an herbicide once every 10 to 14 days, or until the weeds stop growing.
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The Claim:

Place a container of beer in your garden to destroy slugs.

The reality: Beer will indeed keep slugs at bay! Dig a small hole in the ground so that the lip of your vessel is even with the soil. Fill the container with beer to an inch below its top. Slugs are attracted to the smell, slink into the drink and drown. Slugs have exotic taste: The darker the beer, the better.
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The Claim:

Put citrus peels on ant mounds to control the insects.

The reality: The peels by themselves don’t effectively control insects because the ants can simply carry them away. However, you can buy citrus sprays (they’re sold as household cleaners) that contain d-limonene oils from peels, and they do kill ants. (Never spray these products directly on plants, though, because they burn leaves.) You can make your own ant-clobbering brew by soaking the grated rinds of two oranges overnight: Mix 1 or 2 Tbsp. soap with 1 cup boiling water, then add the peels. Cool before putting into a spray bottle.
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The Claim:

Sprinkle coffee grounds on soil to give plants a boost.

The reality: Go ahead and treat your plants to this natural pick-me-up. After you’ve brewed your morning blend, spread the leftover coffee grounds across the surface of the potting soil. Be sure not to use fresh (nonbrewed) grounds, since they add no nutrition.
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