Horticultural Home Remedies: Pros and Cons

Hardly a day goes by without someone suggesting to me a home remedy of some kind for a horticultural problem, swearing up and down that it worked. Or someone asking me if a particular home treatment really works.

I usually listen politely in the first case and try to answer as best I can in the second. Whether these home remedies work or not, they are generally harmless, at least to the person applying them, but sometimes what I’m told is so horrifying that I have to intervene for the safety of the person involved.

The problem with home remedies is that, as a rule, no one has seriously confirmed their validity. To do this, you need a “control plant”: an identical plant on which the treatment has not been carried out and with which you can make a comparison. Only then can we get an idea of the treatment’s efficacy, and ideally we should have repeated the experiment on thousands of plants under very different conditions before we can confirm anything.

African Violet on Television

If I tell you, for example, that since I’ve placed my African violet on the television, it blooms more and that the rays emitted by the television stimulate the African violets to bloom, it may be true… but since I hadn’t verified this result on another identical African violet, on the piece of furniture right next to it, I don’t really have any proof. But I told my two neighbors who repeated it to four others who emailed 15 others. And, just like that, an urban legend (or should I say “horticultural legend”) was born!

But is the fact that I placed a violet on a television and got more flowers proof of anything? Maybe it’s because the TV is closer to the window and it’s the new location that’s causing the difference. Or that, because I can see more of the violet, I’m quicker to notice that it’s running out of water and water it more promptly. Or that the plant was already in bud before I put it on the TV, and nature simply took its course. But too late: the legend has already been launched!

Sometimes True

But what appears to be a horticultural urban legend sometimes turns out to be true. Generations of scientists have laughed at the idea that a simple solution of soapy water could be used as an insecticide, even though generations of gardeners have said the opposite. But one researcher finally decided to test the truth of the belief… and so insecticidal soap, more effective against insects than dish soap and less toxic to plants, was born. No one laughs anymore about the effectiveness of insecticidal soap.

The scientific community is often asked to verify some of these treatments, and some turn out to be valid. Others, however, have no beneficial effect at all. Others have even proved harmful. And in still other cases, there was some veracity, but also some negatives. Let’s take a look at some of these homemade treatments today.

Margarine Makes Plant Leaves Glow

I’ve heard that, to make the leaves of our houseplants glow, we can brush them with margarine (or mayonnaise, or motor oil, depending on which legend you hear). And it’s true… at first. Margarine and other products are or contain fats, and fats can make foliage shine. Except that grease also clogs plants’ stomata (the pores through which they breathe) and can eventually kill the treated leaf. Also, grease catches dust and the plant quickly needs another treatment with margarine (or mayonnaise or…) to loosen the dust caused by the first treatment. As far as I know, neither margarine, mayonnaise nor motor oil are of any use in horticulture.

Cigarettes Can Treat Insects

According to this belief, you can soak cigarettes (or cigarette butts, or tobacco, depending on who’s talking) in water and use it to control insects on plants. And it’s absolutely true… but never do it! This is a good example of how a home treatment can be very dangerous for the person applying it. Yes, tobacco can kill insects, because it contains nicotine, a powerful insecticide. But nicotine in solution is several times more toxic than nicotine in smoke, and this concoction could make its applicator very ill. Incidentally, if you recall your childhood memories, nicotine-based insecticides used to be sold, but were withdrawn from the market after a few cases of fatal poisoning.

The Contraceptive Pill Makes African Violets Bloom

Or orchids. Or geraniums. It all depends on who’s telling this urban legend. You’ll have guessed it’s not true and, even if it were, it would cost a lot less to buy fertilizer. And the consequences of not taking your prescription could be pretty costly too…

Coffee Grounds Can Be Used as a Pesticide

We often hear that coffee grounds can be spread at the foot of plants to repel insects. This is true, but it only works on soil insects. The treatment is not effective on insects that attack leaves, stems or flowers. What’s more, the pomace contains caffeine, and since caffeine is toxic to all insects, it’s not so much a repellent as an insecticide… and it kills both good and bad insects indiscriminately. The effectiveness of coffee grounds as an insecticide is therefore very limited: only 1 or 2 days, after which the caffeine they contain decomposes. Coffee grounds are, however, interesting as a soil acidifier and can be added to compost.

Coffee Grounds Can Keep Slugs Away

False: it contains too little caffeine to be effective against slugs, who happily consume the grounds. Coffee grounds can therefore attract slugs to the garden.

A Soda Bottle Filled With Water and Placed in the Garden Will Keep Groundhogs Away.

One theory is that the groundhog looks into the bottle, is frightened into thinking it sees a bigger groundhog, and leaves. The other says it’s the reflection of the light that frightens him. But field experiments show that groundhogs are not at all bothered by the presence of pop bottles, full or empty!

Baking soda

Black spot on roses can be controlled with a baking soda solution. According to this legend, 15 ml of bicarbonate of soda can be mixed with 1 liter of water, adding a few drops of insecticidal soap to help the bicarbonate adhere better to the foliage. Twice-monthly sprays, from the time the leaves come out until autumn, would be necessary. And it’s true. Sodium bicarbonate has also proved effective against powdery mildew on several plants. It is now part of the pest control regime of many gardeners.

Milk Can Prevent Powdery Mildew

It’s said that a solution of one part milk to nine parts water can prevent powdery mildew on plants. And they say it’s true. You see I’m the first to be astonished, because when this remedy first appeared, I didn’t believe it. The reason for its effectiveness is not known. And, by the way, powdered milk is just as effective as whole milk.

Reading This Column on Home Remedies Can Give You a Green Thumb

Many people have told me this, but it’s not true. The only way to get a green thumb is to experiment with plants yourself, and learn from your successes and failures. It’s true that other people’s advice can always help, but the real green thumb is between your ears!

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Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This article on tips for caring for your houseplants was originally published in Le Soleil newspaper on August 21, 2005.