The internet is full of home remedies for the garden. Sometimes it’s easier to grab something from the pantry rather than heading to the garden center to buy a chemical. But do they work? Maybe so, maybe not. Here are a few popular remedies, and the science behind them.
Soap spray – Soap sprays are effective against small soft-bodied insects like aphids. While your liquid dish soap might work, it may also contain grease fighting agents and other additives that could harm your plant – after all, the manufacturer is concerned with cleaning dishes, not killing insects. Insecticidal soaps are specifically formulated for maximum insect damage. The spray must contact the insect, so using it as a preventative won’t work. And be very careful when using any soap spray during hot weather or drought, as it can burn the leaves.
Baking Soda – Baking soda sprays are widely touted as fungicides – I use them myself for powdery mildew on spring cucumber leaves. They work by raising the pH on the leaf, making it inhospitable for fungal growth, and are best for prevention or when disease levels are low. But be sure to measure accurately – like many home remedies, too high a concentration turns a help into a herbicide. One tablespoon per gallon of water plus a spreader-sticker is the usual recommendation. Don’t spray during the heat of the day, and reapply after rain. Excessive buildup can harm the plants, so spray at most every couple of weeks. (Yes, those last two sentences make it fairly ineffective in rainy Florida summers!)
Milk – There have been several studies on milk sprays for aphids, viruses, and powdery mildew. While many show that milk can be beneficial, especially as a preventative, the reason it works is not clear. Also, different studies use different types of milk – several just specify “fresh” cow’s milk. Do they mean raw milk straight from the cow? Non-Fat? Pasteurized? UHT (Ultra-high temperature) pasteurized? Each of these types of milk could have very different anti-fungal or anti-bacterial properties.
So is it worth using milk as a preventative measure? Since it is non-toxic, relatively inexpensive, and won’t hurt the plant, sure. Given the disparity in study methods, it’s hard to say what an effective routine would be, but a 20% – 30% solution of milk in water, sprayed up to twice a week, is a general guideline. Be aware, at least one study noted that higher concentrations can cause mold to grow on the leaves, but it does not appear to harm the plants.
Aspirin – I was baffled by the recent spate of articles recommending grinding up an aspirin and mixing it with the soil when planting tomatoes. A little searching located the source for this recommendation – a USDA study which found a foliar spray followed by a soil drench of aspirin can trigger anti-fungal defenses (systemic acquired resistance) in tomatoes, making it an effective preventative treatment. It was theorized that the salicylic acid in the aspirin was the key, meaning that other pain relievers like ibuprofen or acetaminophen won’t work. Other studies have looked at adding salicylic acid to hydroponic tomatoes and soil drenches for stress tolerance, with good results. Too much aspirin caused yellowing leaves – again, that fine line between help and herbicide.
So does crushing an aspirin and adding it to the soil work? I can’t say, as I can’t find a study using that method. As a foliar spray or soil drench at the correct rates, studies show it should be effective against some (but not all) diseases. A Master Gardener at the University of Rhode Island reported good results with 1.5 uncoated aspirin dissolved in two gallons of water. It was a garden experiment, not a scientific trial – maybe the plants would have been healthy anyway. But the aspirin didn’t seem to hurt. As always, don’t spray very young seedlings, avoid spraying in hot weather, and use a spreader-sticker to keep the spray from running off of slick leaves.
So if you think that all sounds very wishy-washy, it’s because getting rigorous scientific studies designed, funded, and executed is no simple task. Often results are over-inflated or misinterpreted by the media (such as the famous – and nonexistent – Cornell Formula), so it always pays to try to find the source of the claim. Typing “EDIS” in your search will get you the latest Florida-specific UF research, including this great publication on Natural Products for Managing Landscape Pests. And when in doubt, call the Plant Clinic at your local county UF/IFAS Extension Office – that’s what they’re there for!
This blog post was written by UF IFAS Extension Orange County Master Gardener Volunteer, Mary Ann Pigora, class of 2017. The UF /IFAS Extension Orange County Master Gardener Volunteers play a crucial role in the outreach of UF/IFAS Extension.