What Effects Can Laundry Detergent Have on Plants?

Faster Growth

• Some kinds of plants grow faster and stronger when irrigated with detergent water. That's because these detergents contain phosphates, which give them better cleaning power in hard water. According to the Danube Regional Project and the University of Colorado at Boulder, this action can cause nuisance plants, including algae, to overgrow in rivers and other waterways. If you irrigate your garden with detergent water, it may make the plants grow healthier, but runoff could also damage nearby streams.

Damaged Foliage

• Irrigating with gray water containing detergents is best done at the ground level, via underground pipe or soaker hose. Spraying detergent water directly onto foliage allows the detergent to penetrate plant cells and dehydrate the leaves. This dehydrating action is why some detergents are used to kill pest insects. Spraying detergent water on your plants' leaves to irrigate them can actually backfire, causing overall water loss and scarring on affected leaves.

Improved Nutrition

• Many detergents contain nitrogen, an important plant nutrient. Most chemical fertilizers are nitrogen based. Plants irrigated with detergent water may be bigger and healthier looking than plants irrigated with ordinary water. According to Shoalhaven Water, irrigating plants with high-nitrogen gray water can reduce the need for artificial fertilizers and the overall cost of gardening. Just like high-phosphorous detergents, runoff from gardens irrigated with high-nitrogen detergent water can have a negative effect on nearby ponds and streams.

Soil Salinity

• While detergents can increase plant growth in the short term, they tend to damage soil quality in the long run. Most conventional laundry detergents have high salt levels. This salt is carried into the soil by the water where it builds up over time. Too much salt in the soil can weaken or even kill garden plants except for very salt-tolerant varieties. Shoalhaven Water suggests using concentrated liquid detergents, which contain less salt than powders and unconcentrated detergents.