Tomatoes (Lycopersicon esculentum) are one of the home gardener's favorite plants, largely because a freshly picked, homegrown tomato and a store-bought tomato are so dramatically different. Growing them successfully can sometimes be challenging, so gardeners often turn to popular home "remedies" such as Epsom salts or vinegar to give themselves an edge. While you can use vinegar successfully with tomatoes, there are only a few specific cases where it's genuinely helpful.
Vinegar can be used successfully with tomatoes in a few specific ways, but it may be an exaggeration to say it's "good" for the plants.
Using Vinegar to Kill Weeds
One widespread folk usage for vinegar is as a weed killer, to suppress stubborn weeds that might compete with your tomato plants or, even worse, act as hosts for pests or vectors for tomato diseases. While there is a scientific basis for this, there are also a couple of important limitations you should know.
First, the acid found in vinegar will indeed kill weeds by disrupting their cell walls. The cells rupture, their fluids escape and the plant withers and dies. This is good up to a point, but the effect is limited. First, household vinegar — even at full strength — isn't strong enough to quickly and reliably kill the weeds, according to the University of Minnesota Extension Service. For that, you'll need to use something called horticultural vinegar, which is 20 percent acetic acid or higher compared to household vinegar's 5 percent.
There are a couple of further problems. One is that even at this concentration, the acid only kills the part of the weed it comes into contact with. The roots will survive and grow a new weed. A second is that the acid will kill your tomato plants just as effectively as anything else. A third issue is that horticultural vinegar is a strong corrosive, and you'll need to follow strict guidelines to use it safely. In the end, it's no more effective than pulling or hoeing weeds the traditional way, so you'll need to decide whether messing with a strong acid is preferable to the wear and tear on your back.
Vinegar for Blossom-End Rot
One of the more common troubles afflicting home tomato growers is blossom-end rot. It's exactly what the name suggests: The blossom end of your tomatoes will begin to rot and turn black, eventually ruining the entire fruit.
The rot is caused by a calcium deficiency, either because the soil's calcium has been depleted or because you haven't been watering the plants consistently (when the soil is dry, the plants can't absorb calcium from it). If you've been watering your plants consistently, and you're seeing signs of blossom-end rot, vinegar can play a role in rescuing your tomatoes.
Save up your eggshells at a rate of roughly one eggshell per tomato plant and grind them to a powder in a spice grinder or blender. Dissolve the eggshells overnight in vinegar, then add the calcium-rich solution to your water the next day when you water the plants. According to Texas A&M's AgriLife Extension, the vinegar will help speed the tomatoes' uptake of calcium from the eggshells.
Vinegar as a Fungicide
One final widespread use of vinegar with tomatoes is as a fungicide. Tomatoes are prone to a number of fungal diseases, including early and late blight, leaf mold and anthracnose. You can use a commercial fungicide to deal with those, of course, but a simple mixture of vinegar and water is widely recommended as a home remedy. It isn't yet well-verified by science, but many gardeners and gardening experts suggest it.
To use the mixture, stir 2 to 3 tablespoons of white or apple cider vinegar into a gallon of water and mist it thoroughly over the affected tomato plants on both the tops and undersides of the leaves (fungi often begin to grow on the undersides). Vinegar will wash away quickly if it rains or if you water your plants from above, so you'll need to reapply it frequently.
It's best to test your homemade spray on a small area of the plant first to see if it damages the leaves. If it does, dilute the vinegar with a few more cups of water and try again on a different plant.
- University of Minnesota Le Sueur Extension: Vinegar and Epsom Salt as Herbicides
- Texas A&M Extension: Tomato Trials Show Fertilization, Grafting Are Keys to Success
- Fafard: Beating Tomato Pests and Diseases
- Old Farmer's Almanac: Powdery Mildew Remedies for Plants
- Missouri Botanical Garden: Lycopersicon esculentum
Fred Decker is a trained chef and prolific freelance writer. He was educated at Memorial University of Newfoundland and the Northern Alberta Institute of Technology. His articles have appeared on numerous home and garden sites, including OurEverydayLife, GoneOutdoots, The Nest and eHow, as well as the San Francisco Chronicle's SFGate.com.