A number of synthetic detergents and soaps contain volatile chemicals and substances that can have a negative effect on the normal growth of plants. According to some scientific researches, low concentration of some detergents may be beneficial for plant growth. It is best, however, not to risk the health of the plant.
Detergents containing sodium, chlorine bleach and boron may have negative effects while potassium, ammonia and phosphate show good effects on plant growth, according to harvestingrainwater.com.
Detergents containing harmful ingredients cause damage to the soil structure by raising the alkalinity of soil. Consequently, the damaged soil deteriorates healthy plants. Some bleaching detergents kill the good bacteria in the soil.
According to cababstractsplus.org, upon interaction of plants with low concentration of a detergent, several plants show signs of better growth and development.
In some situations, such as in the case of a drought, people may use recycled laundry water for irrigation. Therefore, if detergent-plant interaction becomes inevitable, you may consider switching to potassium-based detergents.
Ordinarily, you should avoid using detergent water for watering plants as the toxic chemicals can cause the plants to die.