Will Dish Soap Hurt My Flowerbeds?

Will Dish Soap Hurt My Flowerbeds?
Gardeners often make homemade insecticidal sprays from dish soap and water, and the spray helps to control a number of common garden pests. Some environmentally conscious homeowners recycle dishwater by using it to irrigate flowerbeds. Usually, small amounts of well-diluted dish soap don't hurt flowerbeds, and soapy water is better than no water for plants during a drought. Don't assume that dish soap is completely safe, however. It must be applied according to certain guidelines to prevent plant damage.
Understanding Insecticidal Soap Spray
An alternative to highly toxic insecticides, insecticidal soap spray is effective against soft-bodied pests such as aphids, spider mites, scales, thrips and mealybugs; it may dissolve the pests' waxy outer cuticle. The soap doesn't kill as effectively wasps, flies, beetles and other insects with hard outer coatings, which makes it safer for beneficial insects such as lady beetles and bees. Insecticidal soap shouldn't be used, however, if you notice honeybees or lady beetles on plant leaves.
Mixing a Spray Solution Safely
Although commercial insecticidal soap sprays are readily available, homemade sprays made from liquid dish soap are safe to use if they are prepared properly. A weak solution made of 2 tablespoons of liquid dish soap mixed with 1 gallon of water is effective and won't harm most ornamental plants. If that weak solution doesn't work, up to 5 tablespoons of liquid dish soap can be mixed with 1 gallon of water, but use the soap with care because a strong solution is more likely than a weak solution to damage plants. Avoid using an ultra-concentrated dish soap to make insecticidal soap. Also avoid using products with ingredients such as degreasers, power scrubbers, air fresheners, bleach, fragrance, lotion and antibacterial agents to make an insecticidal soap because they may damage plants.
Spraying Insecticidal Soap
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And insecticidal soap spray should be reapplied to pest-affected garden plants every four to seven days until the pests are controlled. Unlike chemical sprays, insecticidal soap spray kills only when it coats an insect. The spray has no residual affect and is no longer effective after it dries. Insecticidal soap spray is safer and more effective when applied to healthy, well-watered plants and may damage weak or sensitive plants. If you are unsure about a plant's sensitivity or health, then spray an inconspicuous leaf on the plant, and check it for signs of damage 48 hours later. Early morning is the best time to apply an insecticidal soap spray, which should never be used when the temperature is above 90 degrees Fahrenheit or when the sun shines directly on the plants being treated.
Using Dishwater for Plants
Many public health officials recommend that dishwater, also known as graywater, be used for watering plants only when fresh water isn't available for irrigation. Although dishwater will keep plants alive, it may contain food particles and other materials that can attract rodents and insect pests to the flowerbeds on which it is used. If you use dishwater for watering your flowerbeds, then it's critical to take precautions to keep the beds' plants and soil safe. Avoid pouring dishwater directly at the bases of plants because it may cause root and stem rot. Pour the dishwater evenly on the soil around the perimeter of each plant. Apply dishwater along a tree's or shrub's drip line. A drip line is an imaginary line, or circle, on the ground where water drips from a plant's outermost branches. Dishwater from dish soap that contains bleach shouldn't be used to water any kinds of plants. If your home has a water softener, then use dishwater sparingly because the water contains a higher level of sodium than normal water; sodium can harm plants over time.
M.H. Dyer began her writing career as a staff writer at a community newspaper and is now a full-time commercial writer. She writes about a variety of topics, with a focus on sustainable, pesticide- and herbicide-free gardening. She is an Oregon State University Master Gardener and Master Naturalist and holds a Master of Fine Arts in creative nonfiction writing.