Horsetail (Equisetum arvense) is a very invasive fern (yes, botanists have recently decided that it is no longer a “fern relative”, but a true fern) that many gardeners must remove regularly from their gardens. But as long as you’re yanking it out, isn’t there something you could do with it?
Of course, it’s not a question of adding living horsetail rhizomes into the compost bin, as they may survive the composting process and then invade your gardens again when you use the compost. However, there is another way you can use horsetail…
It so happens that horsetail is very rich in silica (up to 8% of its dried tissues). In fact, more than any other plant. And silica helps plants to better resist disease. So why not prepare a homemade horsetail spray, useful in helping prevent various fungal diseases such as powdery mildew, black spot of roses, gray mold (Botrytis), mildew and some rusts?
To this end, let 2 ounces (50 grams) of fresh horsetail macerate in 1 quart (1 liter) of water for 24 hours, then boil for 15 to 20 minutes and let cool. Filter to remove the leaves and rhizomes (which can now be safely added to the compost bin).
Add 1 cup (250 ml) of the concentrate to 1 quart (1 liter) of water and spray every 2 weeks on plants subject to disease, such as vegetables, phlox, bee balm and roses. Plants are readily able to absorb minerals, including silica, through their foliage.
Alternatively, you can water the plants with the decoction, which will allow them to absorb silica through their roots. This is less efficient than spraying, though, as soil organisms will also take their share of the silica before it reaches the plant roots.
Note that, as with commercial fungicides, horsetail spray can’t cure a disease once the symptoms are visible; at most it can slow its progression. Logically, therefore, it should be applied as a preventative treatment to healthy plants that are prone to fungal diseases.