Garden miracles or garden myths?

You can believe everything you see on the Internet, right? You can take for gospel every Facebook post, Tweet, Pinterest pin and Instagram photo, correct?

It seems like many people get their gardening advice from shared content on the Internet and become unwitting victims of Internet myths. While these gardeners and those who share the false information may do so with the best of intentions, they still help to perpetuate myths that make gardening harder, and maybe even more dangerous, than it should be.

This week we’ll take a look at some of the myths and what you should do instead.

Myth 1: Vinegar weed killer

This is one that I see quite frequently. Well-meaning gardeners want an easy way to control weeds without the use of traditional herbicides. The version I see most uses vinegar in combination with dish soap, which acts as a surfactant to make the vinegar spread over the plant.

The gardener is supposed to apply the vinegar to the plant, preferably on a hot, sunny day and wait for miraculous results.

The problem is, though, that the vinegar is going to do a disappointing job as a weed killer. Sure, the parts of the plant where the vinegar touches will likely be damaged and turn brown. On small plants, this may be the entire leafy, above-ground part of the plant. On large plants, it is unlikely that the whole plant will be damaged.

It is nonselective, so any plant that it touches can be burned. And the big problem is that this does nothing to kill the roots.

If the plant is a small annual, this application of vinegar may very well take care of it. But for larger plants, it may take many, many more applications to take care of the weed problem.

The problem is even greater if you are dealing with perennials that come back from the roots — the vinegar does nothing to damage them, and the plant will be back within the next few weeks.

Household vinegar that you buy at the grocery store is 5 percent acetic acid and 95 percent water.

Some of the sources say that you should find more acidic versions, such as a 20 percent solution that is sometimes called horticultural vinegar.

This product, though, is much more dangerous than even traditional herbicides such as RoundUp.

Contact with skin will result in burns, and blindness can result from eye contact. Your nose will burn and water from just the smell of it. And it will kill small wildlife such as frogs and insects on contact, which is something even RoundUp won’t do.

Instead of falling for the vinegar trap, you can look at other weed control methods. Traditional herbicides can be used safely when applied sparingly and according to label instructions.

Using heavy wood mulches and landscape fabric in beds will also cut down on the need for herbicides. In lawns or in empty garden beds, using black plastic to solarize the soil to “cook” any weeds or residual seeds in the soil can be effective.

Even repeated, severe mowing can wear out some difficult weeds.

Myth 2: Marigolds repel pests

This myth has been around since well before the age of the Internet, but it has spread even farther thanks to posts, tweets and pins.

This practice says that planting marigolds around your garden will ward off insect pests and nematodes, which are soilborne, microscopic, wormlike critters that damage plant roots.

It is true that relatives of marigolds do produce chemicals that repel or even kill insects. Pyrethrin chrysanthemums produce a compound that is extracted and sold as an organic insecticide.

Marigolds do produce an odor that seems to repel other things, such as deer. But little to no evidence has actually been produced to show that this practice results in the reduction of pests in the garden. Even if marigolds did produce a chemical to repel or kill nematodes, in order for it to work the marigolds would need to be chopped up and plowed into the soil.

If insects are a problem and you want to control them organically, use one of the products that does contain the pyrethrin extract as a good, general insecticide. Unfortunately, nematodes can be difficult to control. Solarization like that described above for weeds can help, as can rotating crops. You’ll know if you have nematodes if your plants aren’t doing well and the roots look all knotty and damaged.

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