Gravel has a number of uses in the garden, from improving drainage in potted plants to acting as weed-preventative mulch. Gravel can become a carrier for pathogens that attack plants, however, so it should be thoroughly cleaned and sterilized before it is used in a new location. Gravel can be sterilized with common household chemicals like bleach. It can also be heat-sterilized in the oven or with boiling water.
Rinse Your Rocks
Before you sterilize gravel, wash off all residue or debris that may be clinging to the rock. Common garden applications such as fertilizers and pesticides can react to cleaning chemicals. Perlite, which is often in potting soils, releases toxic levels of fluoride when exposed to high heat. The gravel could kill plants it comes into contact with after being exposed to the fluoride. Removing these substances from the gravel before sterilizing is an important safety precaution.
A Bleach Bath
Household chlorine bleach is an effective sterilization agent for garden gravel and rock. Chlorine begins to break down quickly after being mixed, becoming half strength in as little as two hours. Bleach should be mixed immediately before using and only be used in well-ventilated areas. Soak gravel in a solution of 9 parts water and 1 part bleach for 30 minutes. The levels of chlorine in bleach are toxic to some plants so the gravel should be rinsed well after being removed from the bleach solution.
Heat is a good way to sterilize gravel without chemicals and will kill viruses like tomato-tobacco mosaic virus that are immune to chlorine. Place the gravel in a heat-resistant container. Pour boiling water over the gravel until the gravel is completely covered. Leave the gravel in the boiling water for five minutes. The gravel can be removed from the boiling water after five minutes. Large amounts of gravel may be difficult to remove from boiling water but can be left in the water until it is cool enough to handle safely.
Gravel can also be heat-sterilized in the oven, although this can leave a lingering odor of soil or earth in the oven. Place the gravel in a deep pan and add a little water to moisten the gravel slightly. Cover the pan tightly with foil. Place the pan in the oven and heat to 180 degrees Fahrenheit for 30 minutes. Remove the gravel from the oven and allow to cool completely before using or handling the gravel.
- Penn State Department of Horticulture: How to Pasteurize Medium and Sterilize Containers and Tools
- University of Georgia Extension: Growing Indoor Plants With Success
- Purdue University Cooperative Extension: Indoor Plant Care
- University of Massachusetts Extension: Cleaning and Disinfecting the Greenhouse
- Cornell University: Mulches for landscaping
- University of Minnesota Extension: Tomato-Tobacco Mosaic Virus Disease
- Photo Credit Hemera Technologies/AbleStock.com/Getty Images