The mulch in your garden is attractive, helps keep your soil moist and also provides a comfortable home for ants. They like snuggling down into the wood chips and instinctively know that the mulch circle won't be disturbed. Good for the ants. Bad for you.
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However, cedar mulch repels ants and is suggested to combat problem insects. The fragrance associated with cedar may be attractive to humans, but ants and other insects don't like the aroma of cedar. Not all wood is repellent to insects, though, and Western red cedar mulch works best to control ants, especially as a carpenter ant killer.
About Cedar Mulch Ant Repellent
Cedar has long been known as a moth repellent. Hang it in a closet, and your wool and cashmere sweaters, coats, mittens and hats are safe from moth holes. The natural chemicals in cedar – the phenols and acids – are natural pesticides. Phenols are toxic, and when they enter the insect's respiratory tract and then the blood system, they prove fatal to the liver. The acids damage their trachea and lungs. The earthy fragrance of the cedar becomes a trap, alluring the insects, and ants are no exception.
An organic mulch such as cedar also attracts aphids, which secrete honeydew which is attractive to ants. By deterring the aphids, the ants look to find another source of sweetness. Mulch also keeps the ground moist which is another invitation to ants. Lay the mulch no more than 3 inches thick around the plants, keeping the circle away from the trunk or the foundation of your house.
Create an Ant Resistant Landscape
Any type of wood is at attractant to insects. Ants and termites top the list, so if you want to create an ant-resistant landscape, go for gravel. It's cleaner and doesn't harbor insects. It may be more expensive to lay but doesn't have to be replaced annually like mulch. Mulch should be totally removed when replacing it with new.
Ants need to eat. Remove their source of food, and you remove the ants. Using rubber chips made from tires is attractive to some homeowners because of the low cost and long life, but the rubber doesn't decompose, is toxic to the soil, and is ineffective at keeping out weeds – but ants won't be your problem when using rubber mulch.
Maintaining Mulch in Your Garden
Just as your plants need attention and care, so does mulch. It soaks up water, making it a comfortable home for insects. Rake the mulch to air it out after a heavy rain or cut back on watering if you find it's becoming waterlogged. But if you find a swarm of ants climbing in and out of the mulch, boil a kettle of water and pour it onto the mulch. Look for the ant nest as well and treat it with boiling water.
Boric acid and sugar mixed into a paste is a delightfully sweet treat for ants. One nibble and they carry the rest back to the queen. The queen and the rest of the ants die from the acid. You can also mix 1/2 teaspoon of liquid dish soap with 1 1/2 teaspoons of vegetable oil into 1 quart of water. Pour into a spray bottle and shake well. Spray the mulch with your solution. This mixture damages the ants' exoskeleton so they suffocate.